Harvard Professor: Do NOT Make These Health Mistakes In 2025! (Especially After 40+) | Dan Lieberman

Dr. Rangan Chatterjee 0:00 I wanted to start with this apparent paradox, this idea that exercise is something that is really, really good for us on so many levels, yet at the same time, it's not necessarily something that we have evolved to want to do.

Dan Lieberman 0:18 Oh, I would say we didn't evolve to do it at all. But yeah, that paradox is what really motivated my last book, Exercised. And maybe to answer your question, I'll give an anecdote, right, which is, um, I use in the book, but, uh, I was just finishing up a previous book, The Story of the Human Body, and I was in Mexico doing some research, and we were studying, you know, runners and people who run, and actually discovered that most of the Tarahumara famous for running don't actually [chuckles] run very much. But anyway, there was this one elder fellow who, uh, was a famous runner, did these very long-distance races, and I was being a good anthropologist and I was asking all kinds of questions. And, and I had asked all kinds of other people the s- exact same questions with a translator. And one of the questions was about training, and everybody had always struggled with this question because, uh, and you know, I was beginning to realize that my concept of training was kind of alien to, um, to the Tarahumara. And this guy just looked at me, and I could tell without even the translator saying anything, he's like, "Why would anybody run if they didn't have to?" And I suddenly had this like bzzt, you know, this little epiphany, right, that, uh, that our concept of exercise is alien to most people, right? And of course, I work in parts of the world where, where people are very physically active. They work hard. Here, here I was in a part of the world where people are h- hardworking farmers. They've got no machines.

Dr. Rangan Chatterjee 1:35 Mm-hmm.

Dan Lieberman 1:35 They've got no running water. They've got... You know, they're doing everything by hand. They occasionally do these long-distance races, which by the way, are a form of prayer. That's why they do them. Um, but the idea of going for a five-mile run in the morning is nuts. Nobody does that. Um, so I think... And, and, and I had this sudden like bzzt, this moment that, yes, we evolved to be physically active, but the kind of what we call exercise, which I define as voluntary discretional physical activity, it's planned for the sake of health and fitness, is a completely modern idea. And furthermore, if you're struggling, if you're a, a farmer or a hunter-gatherer, of course, we were hunter-gatherers for moth- most of our existence. If you're struggling-

Dr. Rangan Chatterjee 2:14 Mm

Dan Lieberman 2:14 ... to get enough energy, right, struggling to feed your family, going for a, a five-mile run in the morning, which is about 500 calories, is a terrible idea, right?

Dr. Rangan Chatterjee 2:24 Yeah.

Dan Lieberman 2:24 Because you... Those 500 calories are, is energy that you could use either on your own body or on, on your, your family, right? So, so, so the idea of doing unnecessary voluntary-

Dr. Rangan Chatterjee 2:37 Yeah

Dan Lieberman 2:37 ... physical activity for no reason other than for your health and fitness when you're already very physically active is nuts. So, so we evolved to avoid physical activity except for two reasons. For when it's necessary or when it's rewarding, right? So play is important and rewarding. Uh, work is, is rewarding. Um, a race might be rewarding. But getting on a treadmill in the morning in a gym, you know, with fluorescent lights in a room with no air, et cetera, working as hard as you can, get- getting absolutely nowhere, there's a reason people dislike it. We, we never evolved to do that.

Dr. Rangan Chatterjee 3:12 Yeah.

Dr. Rangan Chatterjee 3:13 I think that's a very powerful message today. Like, we're having this conversation in 2024. Everyone listening, I'm sure, has been hammered with the message that exercise, that physical activity is good for us. It's good for your body, it's good for your brain, it's good for your longevity, et cetera, et cetera, et cetera. So we've all got the knowledge that we possibly, probably should be moving more. Yet despite having that knowledge, so many of us are simply unable to put that into action regularly, and they start to blame themselves.

Dan Lieberman 3:52 Exactly.

Dr. Rangan Chatterjee 3:53 They start to feel guilty, which is a huge problem that I see and have seen in practice for many years. And you know, we're having this conversation in London. I'm rarely in London these days, but I came last week for a couple of days, and I think the underground station where I took a photo and posted on social media really illustrated your point, which was this beautiful flight of stairs, and on one side was an escalator going down, the other side an escalator going up, and literally there was nobody on the stairs, and both sides of the escalators were full. And I posted not... And the first thing I said is, "This is not a post about blame." But I thought it just beautifully illustrated the problem that we have in modern society, which is why would you choose [chuckles] to take the stairs if you don't have to?

Dan Lieberman 4:41 It's an instinct. Of course, it's an instinct to take the escalator. There were no escalators in the Stone Age. Um, I think I can say that with definitive knowledge, right? Um, there were no elevators, lifts, as you call them here in England. N- but, but it's an instinct to save energy when you can. Um, the, the escalator scene that you describe has actually been studied. There are actually a series of papers that have been now done in many different countries. It's been done in the US, in Sweden, Israel, Japan. I can't remember where else.

Dr. Rangan Chatterjee 5:06 Mm-hmm.

Dan Lieberman 5:06 And it doesn't matter where you are on the p- on the planet, when there's a staircase next to an, uh, an escalator, only less than 5% of people take the staircase, and it doesn't matter what culture you are, it's, it's a universal. It's because it's an instinct to, if you can save energy, you, why wouldn't you, right?

Dr. Rangan Chatterjee 5:23 And I'm, I imagine that our hunter-gatherer ancestors would also have taken the escalator had that option been available to them.

Dan Lieberman 5:34 Of course. And it, you know, um, turns out, so, um, some, some of my, some of my former students actually measured how much hunter-gatherers sit.

Dr. Rangan Chatterjee 5:42 Mm-hmm.

Dan Lieberman 5:43 Turns out the average hunter-gatherer, because we're always told that we sit too much, right? And that's, you know, our chairs are out to kill us and et cetera, et cetera. Uh, and that, you know, we are, we're in a, we're in a, in a kind of over-sitting society. Hunter-gatherers sit about 10 hours a day. That's the same as most Americans and, and Brits, right? So- [laughs] So, so they're, they're no different from us. They-- When they can, they sit down. I mean, there are some differences in their sitting, which we can maybe talk about later on, but, but, uh, it's, um... But I think going back to your point, I think in addition to the fact that it's an instinct not to, not to exercise, right? Not to be physically active when it's neither necessary nor rewarding, that we also, we also engage in this, in this form of blame or shame, right? If people are made to feel lazy, if you don't exercise, for some reason you're lazy. And, and, and you have to remember that we're asking people to overcome a very deep-seated instinct, right? And so-- And then people feel bad about themselves because they feel that, sure, I mean, they wake up in the morning, and they think, "Well, yeah, I should go for a run," or, "I should do this"-

Dr. Rangan Chatterjee 6:40 Mm.

Dan Lieberman 6:40 "... or I should lift some weights or something," and then they, and they, and they don't do it for one reason or another, and then they feel really bad, right? And then we made-- And then they think that, well, they're lazy. There's something wrong with them. They're actually normal, right?

Dr. Rangan Chatterjee 6:53 Yeah.

Dan Lieberman 6:53 They're completely normal human beings, and we-- I think our job is to try to figure out how to help people be physically active, to maybe not even exercise, but how to be physically active in a way that, um, that doesn't cause that kind of... You know, do, do it in a positive way rather than a negative way. And, and I think, and no offense, I know 'cause you're a physician, but you're a, a physician that cares s-seriously about prevention. But I think one of the problems is that we've medicalized exercise.

Dr. Rangan Chatterjee 7:21 Yeah.

Dan Lieberman 7:21 We consider it a pill, right? And nobody likes to take pills. Nobody likes to... You know, it do- it doesn't make it fun. It doesn't solve that particular problem of, of overcoming that barrier. I mean, I'm sure you know that most medications, people don't take their medications either. So if they-

Dr. Rangan Chatterjee 7:36 They do, yeah

Dan Lieberman 7:36 ... people don't take their, their, their pills for diabetes or this, that, or the other, why are they gonna take the exercise pill?

Dr. Rangan Chatterjee 7:41 Yeah, because it's often called the magic pill, isn't it? Exercise and, you know, anti-cancer, anti-aging, anti-mental health problems, anti-everything. So perhaps a new PR angle is needed around exercise. I, I love that definition. You know, I, I can't probably get it word for word, but you, you basically said some sort of structured planned activity for the purpose of health and wellbeing.

Dan Lieberman 8:07 Yeah. I think the key word is discretionary. You don't have to do it.

Dr. Rangan Chatterjee 8:10 Discretionary.

Dan Lieberman 8:10 It's discretionary physical activity for the sake of health and fitness.

Dr. Rangan Chatterjee 8:13 Yeah, it's interesting, the, the movements that, you know, our ancestors used to do regularly, and you've detailed them in depth in Exercised, but they're not doing those things for the purpose of health and wellbeing. Like that's a, um, that's a byproduct of doing what they need to do in order to survive, right? So it's, it, it's a, it's a side effect. [laughs]

Dan Lieberman 8:38 So it is a side... I mean, you're right. They, they do it because they have to, right?

Dr. Rangan Chatterjee 8:43 Mm.

Dan Lieberman 8:43 They don't have... If you want to have dinner that day, you have to go out. You have to be physically active to get food, right?

Dr. Rangan Chatterjee 8:48 Yeah.

Dan Lieberman 8:48 It doesn't... There's no Uber Eats in the Paleolithic, right? So you have to go out and get your food, right? You have to go out and find the plants you're gonna eat. You have to go hunt the animals you wanna eat, all of that, right? Um, so it's true. Physical activity was absolutely necessary. But I think that it's not just a side effect. I would argue that human beings, not only like every other animal, benefit from being physically active, but there was special selection in human evolution for, for exercise to be unusually potent for enabling us to live long and healthy lives. And that's, that, that's something that makes us different from every other organism. So to understand that, you have to recognize that we evolved from apes, right? Our closest living relatives are chimpanzees. And, um, well, I've had the good fortune to go out and s- and watch chimpanzees in the wild.

Dr. Rangan Chatterjee 9:35 Mm.

Dan Lieberman 9:35 And let me tell you, uh, you know those, sh- those shows on TV where you watch chimpanzees and they're doing all kinds of amazing, wonderful things? They do that, but very rarely. Most of the time, chimpanzees just sit and eat. Uh, they're incredibly sessile. They're like plants. They just sit there. They spend half of their day literally putting food in their mouth, then they digest that food 'cause it's full of fiber, and then occasionally do some wild, crazy things, have sex, run around, throw things, and then they go back to eating and digesting.

Dr. Rangan Chatterjee 10:04 Mm-hmm.

Dan Lieberman 10:05 And, uh, so chimpanzees turn out to be basically couch potatoes. They're incredibly inactive. Typical chimpanzee walks two to three kilometers a day, takes basi- as many steps per day as a, as a sedentary American. Um, and, um, [laughs] and sleeps 12 hours a night. And that's kind of a chimpanzee life. And then we evolved for two things that are very special in this regard. One is that we evolved to be way more physically active. So we put-- We've got data on hunter-gatherers and subsistence farmers. These people are taking 15 to 20,000 steps a day. Way more than a chimpanzee. They're, they're running, they're carrying, they're, they're, they're climbing, they're doing all kinds of things, right? So they're very physically active. Way more so than chimpanzees.

Dr. Rangan Chatterjee 10:46 Mm-hmm.

Dan Lieberman 10:46 So we evolved to be extra active compared to our ape ancestors. That's one thing. But the other thing that's important is that we also evolved to live very long lives after we stop reproducing. So almost every species on the planet stops, you know, basically doesn't last very long after they stop reproducing. That's because natural selection, sadly, cares about only one thing, and that's how many offspring we have, right?

Dr. Rangan Chatterjee 11:09 Mm-hmm.

Dan Lieberman 11:09 So once you stop having offspring, you enter what's called the selective shadow. I love that term, right? It means that you're, you're basically irrelevant, right? There's no selection to keep you alive after you stop having babies. And humans are one of very few species for which that's an exception, and that's because human grandparents actually play an important role in, in, in helping their children and their grandchildren.

Dr. Rangan Chatterjee 11:32 Mm-hmm.

Dan Lieberman 11:32 And what are they doing? Well, I mean, they're s- they're passing on knowledge and all that sort of thing, but they're also hunting and gathering. They're foraging. Grandparents in hunter-gatherer societies are out there every day. Grandmothers are digging up tubers and other sorts of things and bringing them back for their children and their grandchildren. Grandfathers are out there hunting and bringing back honey and all sorts of things like that. They're, they're, they're physically active. And, and so we evolved to live long lives, not, not retiring, going to the beach and, you know, playing canasta or whatever it is. We evolved to live long lives To be physically active. And in turn, I believe that there's been selection in our evolutionary history for the, for the effects of that physical activity to turn on the mechanisms in our body that help us in- increase our health span, which means increases our lifespan. So physical activity isn't just something you do to get the food. It is. But, but we, but the reason that exercise or physical activity is so healthy is that, that, that we've ha- undergone selection for that physical activity to turn on all kinds of repair and maintenance mechanisms that keep us healthy. And because we never evolved not to be physically active, we never evolved to turn them on to the same extent when we're in- inactive. So instead of thinking of exercise as medicine, I would think of inactivity as being like poison or like not having air.

Dr. Rangan Chatterjee 12:53 Yeah. So it's not necessarily that exercise or physical activity is good for us, it's that the lack of doing it is really harmful.

Dan Lieberman 13:03 Exactly. We call that a mismatch in evolution.

Dr. Rangan Chatterjee 13:05 Yeah.

Dan Lieberman 13:05 It's an evolutionary mismatch. Just like we never evolved not to breathe, right? [laughs]

Dr. Rangan Chatterjee 13:09 Yeah.

Dan Lieberman 13:09 That's a problem, right? We never evolved not to be physically active. And when we stop being physically active, e- everything goes wrong. I mean, literally, 'cause physical activity affects every system in our body.

Dr. Rangan Chatterjee 13:20 Yeah. It, it's, it's so fascinating. Um, in Exercised, you write about, you know, grandmas and, and grandfathers being really active in these hunter-gatherer populations. I think there's a section where you were even writing about how a nursing mother, yes, she still, uh, does some gathering, I think, but you were sort of making the case that the grandmas are way more active, and I thought that was really, really interesting. 'Cause that's quite alien to the common, um, belief, I would say, certainly in Western cultures, that you can kinda slow down a bit as you get older, and that we have this modern phenomena that's retirement, right?

Dan Lieberman 14:02 Yeah.

Dr. Rangan Chatterjee 14:03 Um, so, so speak to that a little bit.

Dan Lieberman 14:05 Yeah.

Dr. Rangan Chatterjee 14:05 'Cause that, that's really interesting.

Dan Lieberman 14:06 Yeah, no, I mean, this... The, the literature's amazing, right? So there's a, there's a anthropologist at Utah named Kristen Hawkes, and she did a study many years ago of Hadza hunter-gatherers. And she showed that the, the mothers are, are digging, you know, several hours a day, getting... 'Cause one of the, the, the mainstay of the diet there are these underground storage organs, tubers, right? So Kristen Hawkes showed that mothers might spend two to four hours a day, I think it was. I ha- have to go back and look at the paper. But it's something like two to four hours a day. Grandmothers are basically twice as active. They're spending twice as much time digging, 'cause why? 'Cause they don't have to take care of the kids as much anymore, although the grand- grandmothers do help a lot with childcare.

Dr. Rangan Chatterjee 14:43 But they're not nursing and breastfeeding, are they?

Dan Lieberman 14:45 Yeah.

Dr. Rangan Chatterjee 14:45 So I guess they've got-

Dan Lieberman 14:46 Yeah, and also their, you know, their kid's not clinging onto them as much, right?

Dr. Rangan Chatterjee 14:49 Yeah.

Dan Lieberman 14:49 So they have more time. So, so they're, they're out there spending more time every day digging up these underground storage organs. And then they're not eating them all themselves, they're bringing them back to camp. And by the way, how do they bring them back to camp? You carry them, right? So carrying. You know, today we, we have maybe little backpacks, et cetera, but, but we don't carry very much anymore. But, but in the life in, in, in, in the Stone Age involved lots of carrying. So they're, they're digging, they're carrying, they're walking. And, and all of that goes until you, until you die, basically. There's no weekends. There's no bank holidays. There's no retirement. Um, there's no, [laughs] you know, social security or, you know, some... its equivalent. You... This is what you do. Um, and, and it's rewarding, of course, but it's also necessary. And that's, and that's how... And that... And I, and I think in turn, that physical activity is, helps them live to be the, to live to be grandparents in the first place. Think about it this way. In, in the West today, a lot of people, as they get older, become less active. We know that from lots and lots of studies.

Dr. Rangan Chatterjee 15:48 Mm-hmm.

Dan Lieberman 15:49 And, and that we, we don't turn on those repair and maintenance mechanisms that keep us healthy, so we're more likely to get heart disease and diabetes and osteoporosis and Alzheimer's, and the list of various diseases is very long. But now we have medicine, people like you, to kinda keep 'em going, right? And so we can, we can enable us to live. We have reasonably long he- lifespans-

Dr. Rangan Chatterjee 16:11 Mm-hmm

Dan Lieberman 16:11 ... even with a lot of chronic disease. So the average American, I think their lifespan is 78, 79. The average health span, the number of years that a average American lives without entering a period of chronic disability, is about 60 something, 63. So the average American spends 16 years before they die in, in a state of chronic disease.

Dr. Rangan Chatterjee 16:32 And, and how does that compare to these hunter-gatherer populations that you've spent so much time with?

Dan Lieberman 16:36 As far as we can tell, they don't have [laughs] that at all. I mean, there's no evidence of diabetes really in, in these populations. There's, there's, you know, heart disease, as far as we can tell, is essentially nonexistent or very, very, very rare. It's very... It's hard to diagnose these disease, obviously, out in the, in the, in the field.

Dr. Rangan Chatterjee 16:52 And have you been to Kenya annually since you were in your 20s? Is that right?

Dan Lieberman 16:55 Oh, gosh, I've been going to Kenya almost every year since 1987.

Dr. Rangan Chatterjee 16:59 '97. A long time. And other countries in Africa.

Dan Lieberman 17:03 Yeah.

Dr. Rangan Chatterjee 17:03 Um, you, you've been, you've been studying these populations, which, which gives you, I think, a rather unique insight into movement and how we as humans have moved for much of our, our past. It's interesting that there's very little heart disease from what you can tell, and of course, there's multiple risk factors for heart disease, uh, lack of physical activity being one of them. But it, it's kind of fascinating to me that some of these populations to, to my knowledge at least, are eating sort of significant amounts of fat in their diets.

Dan Lieberman 17:41 We don't have that much data on hunter-gatherer diets.

Dr. Rangan Chatterjee 17:44 Okay.

Dan Lieberman 17:44 Um, but, um, we just published an analysis, um, last year or two years ago in the American Journal of Clinical Nutrition, where we took all the data on every hunter-gatherer population for which there is diet- good dietary data.

Dr. Rangan Chatterjee 17:56 Mm.

Dan Lieberman 17:56 Turns out there's only about 12 or 13 populations for which we have sufficiently high-quality data to analyze their diets, and there is no such thing as a hunter-gatherer diet.

Dr. Rangan Chatterjee 18:05 Yeah.

Dan Lieberman 18:05 They are incredibly varied. Some of them eat ... a lot of meat, and some of them eat very little meat. Some of the, and, um, uh, it's, it's, there is no one paleo diet. And that's, that's probably one of the problems with the paleo diet. Um, but I would say, like, if you took an average, um, about 30% of the calories in a typical tropical subsistence population-

Dr. Rangan Chatterjee 18:26 Mm

Dan Lieberman 18:26 ... comes from meat. Um, and but also that meat is very different from the meat that-

Dr. Rangan Chatterjee 18:31 Yeah

Dan Lieberman 18:31 ... we eat in the West. That meat has got lower levels of saturated fat. It's, uh, you know, it's a, it's a wholly, it's a different beast, basically. So-

Dr. Rangan Chatterjee 18:38 Yeah

Dan Lieberman 18:38 ... uh, so the meat is not even the same.

Dr. Rangan Chatterjee 18:41 When we're talking about the movement patterns that these populations have had, it, it strikes me as though there's a unity when they move. Let's say you're, you're walking and you're digging for tubers. That has a real purpose, doesn't it, right? You, you, you're doing that because you know that's important for survival, for your, uh, daughter maybe who's nursing your grandchild back at the camp, or whatever it might be. [lips smack] Whereas a lot of the ways we now move as modern humans living in urbanized, uh, settings, is there's almost a lack of unity. And what I mean by that is, you know, we could be, let's say we've motivated ourselves to go to the, the gym, the treadmill in front of the fluorescent lights, okay? Let's say someone has motivated themselves to do that.

Dan Lieberman 19:38 And good for them.

Dr. Rangan Chatterjee 19:39 And good for them.

Dan Lieberman 19:40 Yeah. [laughs]

Dr. Rangan Chatterjee 19:41 Often it's such a tedious pastime for them to do that they will do anything they can to numb themselves away from the activity.

Dan Lieberman 19:51 Maybe they're watching this podcast.

Dr. Rangan Chatterjee 19:52 Yeah. They, they-

Dan Lieberman 19:53 [laughs]

Dr. Rangan Chatterjee 19:53 Someone will probably be watching it now-

Dan Lieberman 19:55 Exactly

Dr. Rangan Chatterjee 19:55 ... or listening to music-

Dan Lieberman 19:56 Right

Dr. Rangan Chatterjee 19:56 ... or watching the news or whatever. Again, so the, the grandma, the hypothetical grandma who you have seen and spent time with, who, who walks, and then is chatting and is digging for maybe four to eight hours a day, and doing that hard physical activity, there's a reason for that. Whereas it feels like we've kind of divorced our body and mind some of the time when we try and move, in terms of I know physical activity is good for me, I need to do it. Oh, I've got to this treadmill, but let me just numb out for the next hour, but I'm still gonna get those physical benefits. Is there any validity to what I've just sort of hypothesized there, and do you see any potential consequence of that?

Dan Lieberman 20:42 Well, I think what you're saying is that w- we have this mind-body dualism-

Dr. Rangan Chatterjee 20:47 Mm

Dan Lieberman 20:48 ... in, in, in our, in our world today. And also we've, we've, because we don't, we're not physically active, I mean, I could, I could have spent my entire day doing almost nothing.

Dr. Rangan Chatterjee 20:57 Mm.

Dan Lieberman 20:58 And, you know, I'm sitting in a chair here. I could have taken the subway here, et cetera, et cetera. And the-

Dr. Rangan Chatterjee 21:02 Yeah

Dan Lieberman 21:02 ... the lift up and all that sort of stuff. So we now have created this weird thing called exercise because it's good for us. But when we do it, we're doing it... There's, there's no purpose for it other than for the sake of exercise, and that is a kind of weird thing. And so, and because it's not fun, we, we try to divert ourselves while we're doing it to decrease how unpleasant it is, right? Make it as, as, as, as minimally unpleasant as possible, right? Um, and that, you know, we've industrialized it, we've commodified it, we've medicalized it. We've, you know, we've... And there's nothing wrong with industrialization or medicalization-

Dr. Rangan Chatterjee 21:34 Yeah

Dan Lieberman 21:35 ... or commodification, but that takes away, uh, the, the, the real kind of, the purpose for it that, that could make it much more, um, uh... I mean, I think it's why people enjoy sports, right?

Dr. Rangan Chatterjee 21:47 Yeah.

Dan Lieberman 21:47 Because when you play a game of football or something, right? You're, you now have a purpose that's-

Dr. Rangan Chatterjee 21:53 Yeah

Dan Lieberman 21:53 ... And you, and, and most people don't think of going for a walk with a friend or playing a game of sport, they don't normally think of it as exercise, right? They think of it as, as you, you're playing a game of football, or you're going for a walk with your friends, and, and that gives it purpose. And I think that's, I think, one of the, I think one of the, the arguments, one of the tricks that we should be using to try to help each other-

Dr. Rangan Chatterjee 22:13 Yeah

Dan Lieberman 22:13 ... be more physically active. Give-- Make it, make it part of our lives. So go for a walk with somebody.

Dr. Rangan Chatterjee 22:18 Yeah. I, I'm not at all criticizing that. I, I myself will do that, uh-

Dan Lieberman 22:22 Yeah

Dr. Rangan Chatterjee 22:22 ... from time to time, right? So I get it.

Dan Lieberman 22:24 Me too. Yeah.

Dr. Rangan Chatterjee 22:25 I just find it fascinating that throughout my career, you know, I'm sure the same is with you, you know, you, you evolve, you know, things that you, you sort of spiral around. You think you've cracked something, and then you, you get some more information, you develop new insights, and you come back round again to possibly where you were before. And I kind of think about this mind-body separation a lot, and I think two things. I think w- we're, we're a time-pressured society because of the way that we work often, and therefore we're trying to fit in our, our exercise and our, our meditation and our mindfulness and our breathwork practice and our... All these things all take time. But actually, let's say someone, you, you mentioned before some tribes run as a form of, like, religious expression. It's, it's, it's a form of prayer.

Dan Lieberman 23:15 It's a form of prayer.

Dr. Rangan Chatterjee 23:15 Right? So it's, there's a real unity there. There's a real mind, body, spirit, if you want, like, connection in terms of what they're doing. And you, you tell this beautiful story, I think, in the chapter on walking and exercise, about when you accompanied two Hadza gentlemen on a hunt. I think you asked them if you could, um, go on a hunt. And it, it, it made me stop and laugh when, you know, they were very minimalist dressed with their kind of sandals, and you had your full gear on and your waterproof trousers and your GPS and your backpack, [laughs] and it, it, it really painted a wonderful image. But one of the things that I, I, that really stood out to me is that you were sort of saying that maybe it was a few hours of walking in silence where they are paying attention, listening, you know, looking for footprints. And I, I kind of felt have, have we lost something here where you could potentially, if you have a mindful walk in nature, let's say you're lucky enough to have nature near you, and you go for a one-hour walk in nature, let's say with a friend or by yourself, but instead of listening to something- You pay attention to the, uh, the, the birds singing, nature, the wind rustling. Like, you're getting your mindfulness meditation, your movement all in one go.

Dan Lieberman 24:30 Absolutely. Yeah. I mean, um, there's a wonderful argument actually that, that the origins of science comes from tracking.

Dr. Rangan Chatterjee 24:37 Mm-hmm.

Dan Lieberman 24:37 Because you're making hypotheses. You're not only observing nature, right? Because, 'cause you need to, right? You're trying to follow an animal, right? But you're also, you're also thinking, you're also trying ... You're making guesses. "I, I think it went to the right. Ooh, let's see. Uh, how would I figure that out? Oh, there are some footprints." I, you know ... So I, I think that you're, you're engaging your, your body and all, and your mind together in an integrated way that is really kind of wonderful.

Dr. Rangan Chatterjee 25:02 Yeah.

Dan Lieberman 25:02 And, and, um, um, and I think that, um, I think that's actually the origin of the runner's high. Because, um, you know, if you, if you do really long-term aerobic exercise, you get this wonderful thing called a runner's high. It's caused by basically endocannabinoids, right, which are the same molecules that give us high, a high when you have cannabis.

Dr. Rangan Chatterjee 25:23 Mm-hmm.

Dan Lieberman 25:24 And, um, and when you get high, right, um, what happens? You have a increased sensory perception.

Dr. Rangan Chatterjee 25:31 Yeah.

Dan Lieberman 25:31 In fact, the first ... One of the first times I got a really good runner's high was actually at the London Marathon, I remember. 'Cause I ran London many, many, many years ago, I ran the London Marathon. And I, I was, I was at a conference and whatever, and I just had fun running it, and I just kind of ran it for fun. And, and at the end, I remember going by Big Ben, because right by the end, and I remember th- saying to myself, "Wow, Big Ben is really big." You know? [laughs] And, and I was having, like, experiences like that.

Dr. Rangan Chatterjee 25:57 Yeah.

Dan Lieberman 25:57 I mean, everything was ... The blues were bluer and, you know, that person's butt was, you know, bigger and, you know, e- all the things I was looking at. And I remember [laughs] when I got to the finish line and I was talking to some of the folks from the medical tent, 'cause I, I was working with, with some, with some medics there.

Dr. Rangan Chatterjee 26:12 Yeah.

Dan Lieberman 26:12 And, and I remember w- the, this guy named Dan Tunstall-Pedoe, who's the medical director of the marathon. He said, "Dan, you need to be very careful on your way back to your hotel because you've got a really serious runner's high." [laughs]

Dr. Rangan Chatterjee 26:24 Right.

Dan Lieberman 26:24 It's like, "Oh, yeah. I guess I do."

Dr. Rangan Chatterjee 26:26 Right.

Dan Lieberman 26:26 But, but why do we have that runner's high? So you ... Because when you're running, you're tracking, and you're picking up all this information, and you're ... And it, it's helping you get more, you know, you're ... Everything you're seeing is now s- heightened. The sensory awareness is higher. And I think ... So, so we actually have adaptations to increase exactly what you're just talking about.

Dr. Rangan Chatterjee 26:44 'Cause I guess the point of running ... And, and I appreciate that you, you do mention that there are these long races that, the Tarahumara often do to, you know, celebrate or as a form of prayer. But generally speaking, the running is done for a purpose.

Dan Lieberman 27:00 Correct.

Dr. Rangan Chatterjee 27:00 So therefore it makes sense that we would have heightened awareness and sensations and maybe sounds.

Dan Lieberman 27:08 Yeah. And everybody who runs knows that or does any kind of exercise, you know that you have this heightened sensitivity. And, you know, it can be fun to listen to ... I, this morning I ran along the Thames, and I had, I had e- headphones and I listened to some very-

Dr. Rangan Chatterjee 27:20 Yeah

Dan Lieberman 27:20 ... very zippy playlist, and that was a lot of fun. But sometimes I run without ... I often run without music, and I find it's a form of meditation.

Dr. Rangan Chatterjee 27:27 Yeah.

Dan Lieberman 27:27 And, and, um, and my mind wanders and, and I look at sights and all that and, and that's really kind of wonderful, too.

Dr. Rangan Chatterjee 27:35 I think when I spoke to Eliud Kipchoge, the Kenyan marathon runner, a couple of years ago, the week after he, he broke the world record in Berlin. From recollection, when he's running with his, uh, running team and his crew, no one's listening to anything.

Dan Lieberman 27:53 Never.

Dr. Rangan Chatterjee 27:54 But he said, I think when he's, like, doing some extra work on his indoor bike, I think he said that's when he'll put on music. Again, to sort of maybe dilute the tedium of something, whereas-

Dan Lieberman 28:05 Sure

Dr. Rangan Chatterjee 28:05 ... you know, wh- which I find interesting. Dan, you've studied the biomechanics of human movement in a number of forms over the years.

Dan Lieberman 28:12 Yeah, that's my day job really. [laughs]

Dr. Rangan Chatterjee 28:14 Yeah. And so, you know, from what you have seen ... And I, you know, like, there's a gorgeous section in the introduction where you said you've played barefoot cricket in India, you've raised horses on foot in Mexico, you've tracked oxen and kudu in Tanzania, you've run and carried water over your head in Kenya. I thought what a rich life you have led. You know, you've, you've studied all these populations as well. But what are some of the key things you've learnt from these more natural populations about human movement that we perhaps have got wrong in terms of how we understand human movement here in the West?

Dan Lieberman 28:53 Um, well, first of all, I think what I've learned the most from, from ... I've been very fortunate. I agree. And I, and I, I'm s- I have the best job on the planet, I think, and I'm incredibly lucky. Um, but I think what I've learned the most is that these folks are just ordinary everybody, everyday folks. They're like everybody, right?

Dr. Rangan Chatterjee 29:12 Mm-hmm.

Dan Lieberman 29:12 And they have the same goals and wishes and desires. They're trying to do better for their children. Um, and they're, and they're working hard, just like people in, in London are working really hard, but they're just working hard in a different way. And there's nothing really special about them. It's just that, um ... But I think the thing that I've learned the most, and ... But I, I, I've learned to really, uh, I, um ... You know, I don't think of them as more natural populations. I just think of them as, as, as just human beings who just live-

Dr. Rangan Chatterjee 29:42 Mm

Dan Lieberman 29:43 ... uh, a, a less industrial life. Um-

Dr. Rangan Chatterjee 29:45 Yeah

Dan Lieberman 29:45 ... but I think what I've learned the most is that it's changed the way I think of what's normal, right? Um, we think it's ... Like yesterday I got in an airplane and flew from Boston to London. And this morning I, you know, my hotel, I had breakfast cereal that came in a box. Um, and I had, you know, milk that came from a, a thing. And then when I wanted water this morning, I just turned a faucet and out it came-

Dr. Rangan Chatterjee 30:09 Yeah

Dan Lieberman 30:09 ... and all that. We think that's normal, and I think what I've learned the most is that the lives that we live today in many parts of the world, especially cities and in, in high-income countries, th- they're not normal, right? And, and, and, and just perceiving that, thinking about that- It's been eye-opening. You know, everything from the sh- footwear that we wear, like wearing cushioned shoes with high heels and all that kind of stuff, to, to the, um, to the foods that we eat, the, the physical activities that we do. They're not normal. They're-- now, there's not no one normal way of doing it, but what we're doing is very abnormal. And, and sometimes that's good. I mean, antibiotics are good. Refrigeration is good. There's, you know, all-- brushing your teeth is good. There's lots of things that I do that are not normal that are good for me, but there's also a lot of things I do that are not normal that are bad for me. And I think the experiences I've had have helped me think a lot more about just what's normal and also think about variation, because there's an enormous amount of variation-

Dr. Rangan Chatterjee 31:06 Mm

Dan Lieberman 31:06 ... out there in the world. If you go to populations in the Arctic versus the tropic and s- you know, the wet-wetter tropics and the drier tropics, et cetera, the variation is stunning.

Dr. Rangan Chatterjee 31:16 Yeah.

Dan Lieberman 31:16 It's stunning.

Dr. Rangan Chatterjee 31:17 You mentioned footwear then. Um, you're probably regarded, I think, as one of the, the godfathers of the minimalist-

Dan Lieberman 31:25 [laughs]

Dr. Rangan Chatterjee 31:26 ... shoe movement. I don't know.

Dan Lieberman 31:27 I'm the, the barefoot professor. Yeah. [laughs]

Dr. Rangan Chatterjee 31:28 Yeah, I don't know how that, how that ha- uh, sits with you.

Dan Lieberman 31:31 [laughs]

Dr. Rangan Chatterjee 31:32 But, um, l-let's go there. You know, you, you, you do mention it quite a bit in exercise as well about the footwear that these less industrialized populations routinely wear. Um, you know, many things in life have got-- they're, they're a trade-off. So there's pros and there's cons. Um, what are some of the benefits do you think of those populations and potentially us wearing, um, kind of less cushioned shoes or, or for want of a better term, minimalist shoes?

Dan Lieberman 32:05 Uh, well, I think the word that you used, trade-offs, is the operative word, right? There are benefits and costs to everything.

Dr. Rangan Chatterjee 32:13 Mm.

Dan Lieberman 32:13 Just about everything on the planet.

Dr. Rangan Chatterjee 32:14 Yeah.

Dan Lieberman 32:14 There might be a few exceptions, but they're hard to think of. And shoes are one of them, right? So shoes-- the big benefit of shoes, apart from the fact that they can look sexy or nice or all that kind of stuff, is that they protect your foot, right?

Dr. Rangan Chatterjee 32:25 Yeah.

Dan Lieberman 32:25 They protect the sole of your foot from damage. And the, and the other thing that we look for in shoes today in, in, in high industrial, you know, wealthy populations is for comfort. So we wear shoes because they, they look good, they protect our feet, and they're comfortable. But the trade-off is that, um, that, uh, is really the most important trade-off is they make our feet weak. So what a shoe does is it kind of does some of the work for you that the muscles in your foot would otherwise do. If you have a shoe that has a-- Like if you've ever gone for a walk on the beach, which I'm sure you have, or gone for a run on the beach, after a, a day of running or walking on the beach, your feet are kinda tired. Why is that? Because when you're pushing off from the, from the sand of the beach, that's a, that's a compliant surface and now you have to, you have to use your foot muscles-- have to work harder to generate force.

Dr. Rangan Chatterjee 33:14 And you're talking about walking on the beach without shoes on.

Dan Lieberman 33:16 Without-- barefoot.

Dr. Rangan Chatterjee 33:17 Yeah.

Dan Lieberman 33:17 Thank you. But if you were to wear shoes, it's a lot easier because you've now made the, the surface now stiff. And so you can push o-- You-- We have this old expression in America, "You can't fire a cannon from a canoe," right? Right? Um, if you push off from a stiff shoe-

Dr. Rangan Chatterjee 33:31 Yeah

Dan Lieberman 33:31 ... right, your now-- your foot muscles have to do less work.

Dr. Rangan Chatterjee 33:34 Yeah.

Dan Lieberman 33:34 And your muscles in your feet are like the muscles in any other part of your body. If you use them more, they, they're stronger, and they-

Dr. Rangan Chatterjee 33:39 Mm

Dan Lieberman 33:39 ... they're larger. And so by having shoes that are stiff, but also having arch supports in them and toe springs and all the fancy schmancy features that we have in our shoes, enable our, our, the foot muscles in our feet to atrophy, um, or not grow to the extent that they normally would have grown-

Dr. Rangan Chatterjee 33:57 Yeah

Dan Lieberman 33:57 ... and, and be as strong. So we've published studies where we've, we've a- we've taken out into the field, um, just an ultrasound, you know. Now we can-- these really cheap ultrasounds that work on a tablet. It's amazing-

Dr. Rangan Chatterjee 34:07 Yeah

Dan Lieberman 34:07 ... the technology. So we can go out and ultrasound people's feet in, in, in Kenya and places like that, in Mexico. And people who don't wear shoes have much stronger foot muscles. That's the best way to measure foot strength, is the s- cross-sectional of the muscles. And we can look at people from the same population who live in the city, who wear shoes all the time, and they have smaller, weaker feet. They also have a much higher percentage of, of flat feet. Um-

Dr. Rangan Chatterjee 34:31 Mm

Dan Lieberman 34:31 ... so actually out in the, in the areas where people are habitually barefoot, we don't see flat feet at all. I mean-

Dr. Rangan Chatterjee 34:36 Yeah

Dan Lieberman 34:37 ... it, it's nonexistent. Uh, whereas you go into the city, you see the same percentage of flat feet as we see in America or in England.

Dr. Rangan Chatterjee 34:44 Yeah.

Dan Lieberman 34:44 So, so I think the big effect is that people's feet have become weak. And, you know, you go to the gym, and you watch people work out, right? I go to the gym sometimes too. And you know how people are working on their biceps and their, you know, their legs and their, you know, whatever. But the one bit they're not working out is their feet because they're now encased in these supportive, cushioned shoes that, um, that have effects. So that's one thing, and there's one more thing, though, which is that when you have cushioned shoes, it also changes how you run. So barefoot people don't land hard on their heels. They have to land softly and gently because it hurts.

Dr. Rangan Chatterjee 35:18 Yeah.

Dan Lieberman 35:18 And now we have these shoes that have all this cushioning, and that not only-- that changes the mechanics of how we run, and when that does that, we end up not feeling the impacts, but the impacts are there-

Dr. Rangan Chatterjee 35:28 Yeah

Dan Lieberman 35:28 ... 'cause they're just slowed down. That actually increases the impulse. That's the area under the curve. It's the integral of the, of the, of the... And that actually shoots up to our knee, and that causes-- we think that causes a lot of knee injuries. So, so shoes make your feet weak, and they also, I think, change the way we walk and run, and that can have negative effects.

Dr. Rangan Chatterjee 35:48 Okay. I've got so many questions.

Dan Lieberman 35:49 That's a long, long answer. Sorry. But it's a big question.

Dr. Rangan Chatterjee 35:51 No, no, no, not at all. I mean, um, regular listeners, uh, to, to this podcast will know what a fan I am of minimalist shoes. I personally have been wearing them since twenty twelve now, so twelve, almost thirteen years, like pretty much exclusively. I see you've got some VIVO- Vivobarefoots on like I have at the moment. Um, just taking a quick break to give a shout-out to Vivobarefoot Shoes. Now, I've been a huge fan of Vivobarefoots for over ten years now, well before they started supporting my podcast. They are the only shoes that I wear, and they really have had a huge impact on my own life and the lives of many of my patients. You see, when people start wearing minimalist shoes like Vivos, you can see improvements in things like back pain, hip pain, knee pain, foot pain. Even things like plantar fasciitis can often get better. And scientific research shows us that just wearing Vivos for about four months or so improves the strength in your feet by over 60%, which is absolutely incredible. One thing people don't realize about these shoes is just how flexible they are, which allows your feet to do what your feet naturally want to do, rather than the shoe dictating your foot's movement. VIVOBAREFOOT are giving my audience a 15% off one-time code when you make your first order, and they make it really easy for you to give them a try. They give a 100-day trial for new customers, so if you don't like them, you just send them back for a full refund. I'm a huge fan. I really hope you take advantage of this offer. To get your 15% off code, all you need to do is go to vivobarefoot.com/livemore or click on the link in the description box below. But I just wanna go back to what you said about strength. So let's make the case to someone who goes, "Well, but why do I need foot strength?" Like for example, they may see the merit in, I don't know, going to the gym. Let's say they're a young guy in their 20s. They, they might fancy the idea of some bigger biceps, right? So they can see, oh, if I work on my biceps in the gym, my biceps are gonna get bigger, which might look good and are also potentially gonna help me carry things, right? So there's a reason that they might want to go and work on their biceps. They might also be thinking, "Dan, yeah, but why do I need my foot to be strong? What benefits is that gonna have for me?"

Dan Lieberman 38:26 Well, if your feet hurt, y- you're not gonna be a happy individual, right? And, and, and having weak feet can cause a wide range of problems. The biggest one is, I think, plantar fasciitis. So the plantar fascia is this connective tissue that runs underneath your foot. It goes from your heel, and it, it's like a, it's a, it's this, it's this very avascular-

Dr. Rangan Chatterjee 38:47 Mm

Dan Lieberman 38:47 ... uh, but highly innervated, [laughs] so lots of nerves in it, but very few blood vessels, that runs from your heel and it wraps un- around underneath your toes, right? And, and it's, um, it's a... We've actually studied the evolution of the plantar fascia. It's an, it's an old feature that evolved long ago. But in humans, it's taken on a new role, and that role is to act as another layer of, of the foot that helps us stiffen our feet when we push off. So humans, unlike, our, um, one of our, one of the unique things about humans is we have an arch in our feet. Uh, like chimpanzees, other, other animals don't have a, that, that arch in their feet. Actually, we have several arches in our feet. There's a transverse and a longitudinal. But anyway, that fascia helps stabilize that arch when we push off.

Dr. Rangan Chatterjee 39:33 Mm.

Dan Lieberman 39:34 But the problem is that it didn't evolve to do it very much, because there are also four layers of muscles in your feet.

Dr. Rangan Chatterjee 39:40 Okay.

Dan Lieberman 39:40 And those are the ones that really, their job is to stiffen the foot. And what happens is that when those muscles are weak, the fascia ends up doing a job it never evolved to really do, which is to do, to take over the job that-

Dr. Rangan Chatterjee 39:52 Mm-hmm

Dan Lieberman 39:53 ... the muscle should be doing. And then what happens is you get, you stretch that fascia, it gets angry, and you get plantar fasciitis, which I'm sure you know, and I'm sure many of the listeners know, is one of the worst-

Dr. Rangan Chatterjee 40:04 Yeah

Dan Lieberman 40:05 ... things can happen. It's awful. Plantar fasciitis sucks. I've had plantar fasci- [laughs] That's actually what got me interested in a lot of this. I, I was a, you know, I'm a runner, and I used to... And if I didn't change my running shoes fast enough, I would get plantar fasciitis, and I would, I got to the point where I was, like, buying running shoes constantly to avoid plantar fasciitis. Now that I've switched to minimal shoes, 'cause I started... 'Cause we published the big barefoot running paper in 2010. It was the cover of Nature. But, um, but I started sort of studying this in the, I would start doing it maybe 2007, 2008.

Dr. Rangan Chatterjee 40:35 Mm.

Dan Lieberman 40:35 I haven't had, I can't even imagine having plantar fasciitis anymore, because I have much stronger feet. So if you wanna avoid plantar fasciitis, you want a strong foot. If you wanna avoid having a, a fallen arch, um, uh, if, an arch, you know, a collapsed arch is no fun either. You know, pe- people develop an arch the first few years of life. Babies are born with a flat foot. You develop it as you start using your foot. And then people, if they stop using, you know, their, those muscles in their feet, the bones of the feet, those muscles get weak and your, your foot collapses again. So again, people have strong feet in the, in, who don't wear shoes. They don't have, uh, fallen arches. They don't have flat feet.

Dr. Rangan Chatterjee 41:12 Yeah.

Dan Lieberman 41:12 So, so those are two good reasons. To have, avoid a flat foot, avoid fallen arches. And, and I think that there's a third reason, which is that it's, it's a proxy-

Dr. Rangan Chatterjee 41:22 Right

Dan Lieberman 41:22 ... um, for using your body, um, as we evolved to use it.

Dr. Rangan Chatterjee 41:28 Yeah.

Dan Lieberman 41:28 And, um, there are all kinds of muscles in our bodies [laughs] we don't use very much anymore. And having strong feet, strong legs, strong everything is just part of being a normal human being. And when one bit gets weak, it's like a weak link in a chain, right?

Dr. Rangan Chatterjee 41:43 Yeah.

Dan Lieberman 41:44 Everything is connected. Everything is connected.

Dr. Rangan Chatterjee 41:46 For sure.

Dan Lieberman 41:46 You can't, you can't just strengthen this and not strengthen that. Everything should be strong.

Dr. Rangan Chatterjee 41:51 Yeah. If I just share my own experience with, uh, transitioning from, you know, regular modern cushioned shoes. I remember when I first went into minimalist shoes in 2012, you know, it takes you a l- little bit. You just got to start getting used to it. Um, but there was a very noticeable impact on my back for the better straightaway. Like, a lot of that stiffness just, just went as a consequence of wearing them. Um, when I started wearing them, people told me I had flat feet. A podiatrist diagnosed me with flat foot. You could see that I had flat feet. I don't anymore.

Dan Lieberman 42:30 Exactly.

Dr. Rangan Chatterjee 42:31 Okay? That, and this is what I think people sometimes don't understand. It's like, oh, now that I'm using my foot muscles, well, guess what? My arch is coming back.

Dan Lieberman 42:38 Uh, this happens over and over and over again. We, we, we published some data on this. I mean, you, you know, this is considered anathema to many podiatrists, but it's true. By strengthening your foot you can actually- You can restore an arch. And, you know, there are a lot of podiatrists out there who say you can't do that, but that's just not true.

Dr. Rangan Chatterjee 42:55 Yeah. It's another example of where I feel in medicine, for all the things that we do well, one of the problems I've always had in my profession is that I feel much of my training and focus is to deal with the downstream symptom.

Dan Lieberman 43:13 Oh, absolutely. So, uh, my previous book, The Story of the Human Body, I came up with a term for this. I c- c- what I call dysevolution. What happens is that we treat the symptoms rather than the causes of problems that are mismatches-

Dr. Rangan Chatterjee 43:25 Mm

Dan Lieberman 43:25 ... like not using, you know, having strong feet. And then we, by, by treating the symptoms rather than preventing the causes, we allow the, the, uh, things to get worse, right?

Dr. Rangan Chatterjee 43:35 Mm-hmm.

Dan Lieberman 43:35 So, so more and more people get flat feet. More and more people get diabetes. More and more people get... I mean, obviously there's no flat feet and diabetes are [laughs] very different levels of things.

Dr. Rangan Chatterjee 43:43 Yeah, but the principle is that-

Dan Lieberman 43:44 But the principle's the same. But I want, I do wanna back up a little bit because it's also true that when we medicalize and commercialize these treatments or these preventive treatments, sometimes we overdo it, too. So when that book Born to Run came out, which, you know, started, you know, arguably in my lab, but a lot of people read that book, and they thought, "Ah. All I have to do is switch to minimal shoes-"

Dr. Rangan Chatterjee 44:05 Yeah

Dan Lieberman 44:05 ... go barefoot, and all my problems will be solved. You know, my teeth will be whiter. Girls will like me more." Whatever, right? "I'll be able to run a s- two-hour marathon." And, and what, and what happened was that people went crazy. They went, they did it too far, too fast. You have to build up strength. You have to learn. If you've been running one way your entire life and you have to lear- learn to run differently, you can't just do it overnight. You have to be gradual. So we, I think we also sometimes oversell-

Dr. Rangan Chatterjee 44:31 For sure

Dan Lieberman 44:31 ... sometimes these treatments. And, and [laughs] I remember my, uh, my wife, I, who also likes... I mean, my wife has, ever since she was a kid, loves to go barefoot, and she loves still walking barefoot. She walks around Cambridge, Massachusetts barefoot all the time.

Dr. Rangan Chatterjee 44:44 Wow.

Dan Lieberman 44:44 But, um, she went to a podiatrist or a orthopedist in, at the Harvard Medical S- Service. Um, and he was like, he was upset about me, and so he knew that she was relate, you know, my wife. And he started saying, "Well, you know, I've seeing all these, these patients now are getting injured because of these, these minimalist shoes, these..." He called them barefoot shoes. And I don't like the term 'cause there's, if you're wearing a shoe, you're not barefoot. But anyway. And, [laughs] and she, she pointed out to him, she said, "Well, that's true, and some of these people are overdoing it. But if y- you're, you're not counting all the people who are also wearing the shoes who you're not seeing."

Dr. Rangan Chatterjee 45:17 Yeah.

Dan Lieberman 45:17 [laughs] And he's like, "Oh. Oh, I never thought about that." Um.

Dr. Rangan Chatterjee 45:21 It's a good point, isn't it?

Dan Lieberman 45:22 [laughs] Yeah.

Dr. Rangan Chatterjee 45:23 But it's also that I- I think when we talk about this topic, we need to be really careful what we're talking about, right? So for example, my current view based upon what I've seen and, and what I've studied, a lot of it being your research, is that a lot of the benefits come when people start living their regular daily life in minimalist shoes, right? So their office shoes. They go to the shops in them. They're... You know, I, I think most people, a lot of people do really, really well when they make that transition. I do think for some people... Look, some people can run in cushioned shoes, uh, and are having no problems. They're running fine, and-

Dan Lieberman 46:11 If it ain't broke, don't fix it.

Dr. Rangan Chatterjee 46:12 Yeah. So I get that. Uh, so I think, I think the whole minimalist shoes things gets conflated with running, and I think running is, sure. Like, I run in, in minimalist shoes, and, but I've been wearing them for 12 years now, and I've been gradually [laughs] doing stuff, right? But it, I think, I don't think you necessarily have to run in them. [laughs]

Dan Lieberman 46:33 No, of course not. Actually, that's one of the things that's mystified me. So when we published the barefoot running paper, and it was, it was the cover of Nature and had a big deal, and it's, you know, and it, it got a lot of publicity. And I thought, "Okay, this is fun. But you know what? What's the most fundamental form of physical activity? It's not running. It's walking."

Dr. Rangan Chatterjee 46:48 Okay.

Dan Lieberman 46:49 And I expected to see people start applying the, the tools that we pu- you know, the arguments-

Dr. Rangan Chatterjee 46:54 Mm

Dan Lieberman 46:54 ... that we published and the, the, the, the methods that we published and the ideas that we published to start working on walking. And yet there's now been thousands of papers in the literature on barefoot running. It's been great for my, you know, citation index. But, but I was like, "Why aren't you guys studying walking? Walking is actually more important." So we've started doing a lot of work on barefoot walking. Published a- another paper in Nature.

Dr. Rangan Chatterjee 47:15 And what, and what does it show?

Dan Lieberman 47:16 It... [laughs] So here's one of the really cool things that we found, was that, um, you know, when you walk barefoot, of course you develop calluses. And calluses are the natural shoe. And one of the reasons we wear shoes is to protect our feet, right? Calluses, people can, can wear, can be barefoot, and they can walk on the most amazing stuff if you have a proper callus, and you don't feel, y- you know, you don't hurt yourself. But what's really cool is, like, unlike a shoe, so when you're wearing a shoe, you don't feel what's under the ground.

Dr. Rangan Chatterjee 47:44 Mm.

Dan Lieberman 47:44 You can't tell what temperature the ground is. You can't feel the pebble that you stepped on, et cetera. But when I started running barefoot, I suddenly realized that I, I could run over an, an acorn or something like that and not hurt me. But I could-

Dr. Rangan Chatterjee 47:56 Right. When you say you were running barefoot, do you mean with minimalist shoes-

Dan Lieberman 47:59 No, barefoot

Dr. Rangan Chatterjee 47:59 ... or completely barefoot?

Dan Lieberman 48:00 Completely barefoot.

Dr. Rangan Chatterjee 48:01 Okay. So-

Dan Lieberman 48:02 Yeah

Dr. Rangan Chatterjee 48:02 ... real barefoot.

Dan Lieberman 48:03 When I say barefoot, I mean barefoot, right.

Dr. Rangan Chatterjee 48:04 Got it.

Dan Lieberman 48:05 And I was, so I was, I, you know, I'd build up calluses. So I had this tradition. I would, like, run the Boston Marathon, which is in April, and then I'd start taking my shoes off, and by the end of the summer, I had really nice, thick calluses. And then I'd put my shoes on again in the winter, right? And I realized that I could run over s- surfaces that would otherwise hurt me, but, uh, but it wasn't that I didn't feel the ground underneath me. It's just that it didn't hurt me. So what, uh, what, what calluses... Because calluses are made out of keratin. It's like what makes-

Dr. Rangan Chatterjee 48:33 Mm

Dan Lieberman 48:33 ... your fingernail or your hair, right? It's stiff, but, um, but it's protective. And so when you're, when you run on, on calluses, you're, like a hair, like a fingernail, it's, it's protecting your feet remarkably well but with no loss of sensory perception.

Dr. Rangan Chatterjee 48:52 That's amazing

Dan Lieberman 48:52 And so we did these studies in Kenya. We looked at people who had thick calluses, 'cause they'd never worn a shoe in their life, and we, we measured their sensory perception. They had... And we ultrasounded their feet, so we knew how thick their calluses were. And they could feel just as well what, what somebody who had almost no calluses had, but they had all that protection.

Dr. Rangan Chatterjee 49:12 Mm.

Dan Lieberman 49:13 And so we... One of the things that's abnormal about our world, we were talking earlier, is, is, is having no calluses on your feet. And I remember, I, when I was, when I was doing a lot of barefoot running, I don't run barefoot very much anymore, 'cause I've just kind of, I don't know, moved on. But, um, I remember one morning I was... There was this, uh, to get to the Charles River from my house, so there's a few streets-

Dr. Rangan Chatterjee 49:32 Mm

Dan Lieberman 49:32 ... I run down, and I often in the morning I would see this woman who was, she has, um, she had two beautiful dogs. I remember-

Dr. Rangan Chatterjee 49:38 Mm

Dan Lieberman 49:38 ... I would see her all the time, and they were gorgeous, beautiful dogs. And I remember one morning as I was running by her, um, she looked at me and she said, "You're not wearing shoes." [laughs] And as I went whizzing by her, I said, "Nor are your dogs." And she was like... The look of shock on her face, like her dogs are not wearing shoes. Oh my God. Right? And but it's normal not to wear shoes, and it's normal to have calluses, but we think it's now weird. People buy pumice stones to get rid of their calluses, right? And, um, so that's just one more way in which our world is abnormal.

Dr. Rangan Chatterjee 50:10 Yeah. I remember as a kid, we'd, we'd go every other summer, we'd go to India, 'cause that's where mom and dad's family, uh, my family, that's where they all stayed. So we'd go for six weeks every other summer. And, uh, you know, some of my fondest memories are, like when I was playing with my cousins, and about 4:00 PM every day in this block of flats, you'd be like, oh, you know, it's, it's kind of playtime downstairs. And so I'm, you know, I was a kid, I wanted to go and play. And they're all playing football barefoot, and I'm used to wearing shoes, you know, in the UK. And you just go, all right. And you know, the first day or two it probably hurts a little bit, and then you're totally used to it and you're like, oh, you can totally play the same level and the same ferocity, but everyone's barefoot.

Dan Lieberman 50:57 Actually, you have to play better because I, I played barefoot football in, with kids in, in, you know, 'cause we work a lot in schools, and you can't kick a ball in a sloppy way-

Dr. Rangan Chatterjee 51:07 Yeah

Dan Lieberman 51:07 ... when you're barefoot.

Dr. Rangan Chatterjee 51:07 Exactly.

Dan Lieberman 51:08 'Cause the shoe enables you to be really sloppy, but when you're barefoot, you learn good technique, right?

Dr. Rangan Chatterjee 51:12 It's the same with running, isn't it? If the sole of your foot can't feel what's happening when you interact with the ground, you could probably be very sloppy with your mechanics-

Dan Lieberman 51:18 Yeah

Dr. Rangan Chatterjee 51:18 ... 'cause it's kind of-

Dan Lieberman 51:20 Yeah

Dr. Rangan Chatterjee 51:20 ... hiding it from you. But-

Dan Lieberman 51:21 I think, yeah, I think the key skill in running is, is to run lightly and gently and not overstride.

Dr. Rangan Chatterjee 51:26 Yeah.

Dan Lieberman 51:26 I mean, that's like 90% of the game. And, and if you go barefoot, it's pretty hard to overstride, and it's pretty hard to hit the ground like an elephant.

Dr. Rangan Chatterjee 51:35 What would your advice be then to people who think, "Okay. Well, that's really interesting, Dan. Um, I'm interested in, uh, maybe not wearing my thick cushioned shoes or my high heels or whatever it might be so much." What do you encourage them to do? 'Cause a lot of people aren't gonna go and walk the pavements and start running completely barefoot.

Dan Lieberman 51:56 Sure. And you don't need to. Um, look, I wear shoes most of the time. Um, I haven't run barefoot for a while. Um, and you know what? It's not the biggest deal. Um, but I think you can benefit from, first of all, walking around your house barefoot.

Dr. Rangan Chatterjee 52:10 Okay.

Dan Lieberman 52:10 Um, I mean, many people do that because it's cleanly. Um, they don't like shoes running around in the house anyway. Um, that's barefoot walking. Depends on how much, you may not do that much. But if you, if you want to try, you know, try a pair of minimal shoes. But if you do use them, you have to build up, right?

Dr. Rangan Chatterjee 52:27 Yeah.

Dan Lieberman 52:27 You can't go from 0 to 100 overnight. And see how you like them. And if you like them and your feet feel better, and it's gonna take some time-

Dr. Rangan Chatterjee 52:34 Great

Dan Lieberman 52:35 ... wear them more, you know. Um, there are some other nice things about minimal shoes. You have a nice wide toe box. Your feet toes aren't scrunched together. And-

Dr. Rangan Chatterjee 52:42 Yeah

Dan Lieberman 52:43 ... there are other things that I think are nice about them too. And there are now quite a few companies out there that make them.

Dr. Rangan Chatterjee 52:47 Yeah.

Dan Lieberman 52:47 And some of them are really kind of sexy and nice and all that, so you know. But if you have plantar fasciitis-

Dr. Rangan Chatterjee 52:53 Don't go straight into them now

Dan Lieberman 52:54 ... don't, yeah, I mean, you need to, y- actually, that's a good time to wear a shoe that to provide you some support-

Dr. Rangan Chatterjee 52:59 Yeah

Dan Lieberman 52:59 ... so that you can actually take the pressure off your... So if you're worried... So b- being barefoot and having stronger feet is gonna help prevent the next bout of plantar fasciitis, but it's not gonna treat. It's actually gonna, it's gonna aggravate a, a, a current case of plantar-

Dr. Rangan Chatterjee 53:13 Okay

Dan Lieberman 53:13 ... fasciitis.

Dr. Rangan Chatterjee 53:14 Yeah. So the short term versus the long term.

Dan Lieberman 53:15 Yeah. So, so you need to be careful about it too.

Dr. Rangan Chatterjee 53:17 Okay. So you mentioned that these hunter-gatherer populations sit for comparable amounts of time to Western urbanized populations. We have been told that sitting is the new smoking over the last few years. What's your take on sitting?

Dan Lieberman 53:33 Well, again, it's completely normal to sit, right? I mean, cows in the field sit. You know, moose sit. Chickens sit. Birds sit. Everybody sits. And, and humans are no different, right? And so when Dave Raichlen and Herman Pontzer and Brian Wood measured sitting among the Hadza, which are a population of hunter-gatherers that are, you know, the most studied because they're the easiest to study, they sit 10 hours a day. [laughs] Um, so the idea that, you know, sitting is this modern Western scourge is just not true. That said, there are important differences between how we evolved to sit and how people now sit today. Now, right now we're having this lengthy conversation, and I'm kind of glued to this chair. But, uh, so what we sit now in the West, we may sit long periods of time, but we tend to live, we also tend to sit for long, uninterrupted bouts.

Dr. Rangan Chatterjee 54:20 Mm-hmm.

Dan Lieberman 54:22 Hours at a time without getting up. But if you look at, at, um, at n- populations that don't have chairs, um, they, they interrupt their sitting bouts co- constantly. They get up to tend the fire, to go pick up a kid, to do a little bit of this, to do a little bit of that. And so, so that's-

Dr. Rangan Chatterjee 54:39 Is that always to do stuff, or is it sometimes because if you don't have a chair you might be sitting in a-

Dan Lieberman 54:44 Oh, absolutely

Dr. Rangan Chatterjee 54:45 ... position that becomes uncomfortable after 20 minutes?

Dan Lieberman 54:47 I think it's a combination of the two.

Dr. Rangan Chatterjee 54:48 Yeah. Okay.

Dan Lieberman 54:49 Exactly. So that's, so, so, so they don't sit for long, uninterrupted bouts. That's one difference. And the other difference is that, um, um, they don't have, like this chair I'm sitting in, I'm now leaning against the back, right? It's not, the chair has been designed to, you know, for ergonomically to have the, the least amount of work that my body's doing, right? And so that means that- I'm not turning on a single muscle in my body now-

Dr. Rangan Chatterjee 55:12 Yeah

Dan Lieberman 55:12 ... except for I'm gesticulating and I'm using the, you know, my mouth, right? Uh, whereas, you know, the modern chair with a seat back didn't become common until the, the Industrial Revolution. Actually, the first mass-produced chair was produced in 1859, an important year for evolutionary biologists, 'cause that's the year that The Origin of Species was published, right?

Dr. Rangan Chatterjee 55:34 Wow.

Dan Lieberman 55:34 And, uh, so, uh, uh, Thonet, a guy in Germany, produced the first... You know, the café chair with those bentwood?

Dr. Rangan Chatterjee 55:40 Yeah.

Dan Lieberman 55:40 That was the first industrialized chair. And now, of course, chairs with backs are, are omnipresent. You go anywhere in the world and those plastic chairs are... You name it. You go anywhere on the planet, people have chairs, right? But that, this chair I'm sitting in and that you're sitting in, now we no longer have to use any back muscles-

Dr. Rangan Chatterjee 55:56 Mm

Dan Lieberman 55:56 ... to keep up our upper body. We're not squatting or sitting on the ground, so we're not using any of the muscles in our legs. And when you, when you... Even that little bit of muscle effort changes... Or, and also getting up every once in a while. So intermittent, you know, s- sitting for, you know, getting up every once in a while, and also using chairs-

Dr. Rangan Chatterjee 56:15 More active sitting positions.

Dan Lieberman 56:16 Exactly. And also, you know, you're having to use your back to stabilize yourself or your quads or your hamstrings, et cetera-

Dr. Rangan Chatterjee 56:21 Mm

Dan Lieberman 56:21 ... to squat or sit on the ground. All of that's turning on your muscles. And you're not using a lot of energy, right? It's not gonna help you lose weight. But just turning on your muscles turns on all these genes, et cetera.

Dr. Rangan Chatterjee 56:31 Yeah.

Dan Lieberman 56:31 You're using up fat in your bloodstream, you're using up glucose in your bloodstream. You're doing all kinds of other things that makes that sitting much less harmful. So-

Dr. Rangan Chatterjee 56:39 And I think for, for me, Dan, that, isn't that really the key take home from your work, which is, let's study these populations, let's observe what they're doing. That can give us an insight into perhaps how we have evolved to live and move and eat [laughs] and all these other things. But we're not gonna go back to that world, most of us. So what can we learn from them and then apply in our modern urban environment? And so what, what, what came to mind as you were describing that is about three years ago or so, you know, we're in London at the moment, but in, in my own podcast studio, I've got a, I don't know if you'd call it a chair. It's called a Moveman. And it's the best thing I ever bought, because it's basically, there's no back to it. I think it's like one of those medicine balls, but with a stable base essentially. So I'm sitting there, um, having these long two-hour conversations, and I feel, my back feels amazing at the end of it because if... I have the con- My muscles are having to do something to keep myself upright.

Dan Lieberman 57:53 Constantly. Exactly.

Dr. Rangan Chatterjee 57:54 And I, I don't give it s- I don't, I don't have one for my guests. They've got an ergonomic chair.

Dan Lieberman 57:58 [laughs]

Dr. Rangan Chatterjee 57:59 Because I'm like, well, if they're not used to that, they may be going all over the place and not be on the mic, right? So I'm like, okay, well, I'll give them a normal chair or a really nice ergonomic chair. But that has been transformative. So, so we can learn from the research that you and your colleagues do and go, okay, well, could we have sitting positions that are less... It's not making them uncomfortable, 'cause who wants to sit at a desk in an uncomfortable way? But using, having to use your back muscles whilst you're sitting at your computer typing, well, even that would make a difference.

Dan Lieberman 58:30 Sure. So I, I agree. I mean, that's, that's one of the reasons I'm interested in this. But I'm also interested in not just people like you and me, but I'm also interested and concerned about the transition that's going on around the world as people transition from being subsistence farmers to living in cities. And to help them not make the mistakes that we've made.

Dr. Rangan Chatterjee 58:49 That we've made.

Dan Lieberman 58:49 Right? So as people... We call this the, the, the physical activity transition, right? It's, so in, for example, we have a project in Rwanda now. We're looking at people as they move from being f- farmers out in the rural areas where they're, you know, they have no machines-

Dr. Rangan Chatterjee 59:02 Mm

Dan Lieberman 59:02 ... and no running water and no electricity, and then they move to Kigali, the big city, and all of a sudden their lives change overnight, right? How can we help that transition occur in a better way, right? 'Cause I think this has global implications.

Dr. Rangan Chatterjee 59:14 Yeah.

Dan Lieberman 59:14 Because, so, so this is not just for people in England. This is for people for everywhere. And, and, and if we can avoid these mismatches, again, we don't have to go back to, you don't have to be a hunter-gatherer.

Dr. Rangan Chatterjee 59:25 Mm.

Dan Lieberman 59:25 But just a simple thing like just changing the way you sit can be important. Or, or having a little, you know, your watch telling you to get up every f- once in a while to remind you just to get up or make a cup of tea or go use the bathroom or whatever. All of that is good.

Dr. Rangan Chatterjee 59:37 Are people receptive? Like, in, in those populations, you're saying that you're, you, you'd love to help them not make some of the mistakes that we have made. Um-

Dan Lieberman 59:46 Well, right now we're mostly studying what's going on.

Dr. Rangan Chatterjee 59:49 Okay.

Dan Lieberman 59:49 And, and, and, and then hopefully having an impact in terms of public health, right? So, so like for example, in Kenya, working with the Kenya National Museum to do an exhibit on this sort of thing that's-

Dr. Rangan Chatterjee 59:59 Right

Dan Lieberman 59:59 ... in, in, in the Kenya National Museum is a, which is the big, you know, museum system in Kenya, to try to, to try to, actually we're trying to use the enthusiasm for running in Kenya to kind of give a public health message about physical activity. Like, you don't have to, you know, be like Eliud Kipchoge or whatever and run a, and win the B- London Marathon or the Boston Marathon or whatever. Just going out for a jog can be a great thing, or just o- other aspects of physical activity. So, so we're... Yeah. So that's-

Dr. Rangan Chatterjee 1:00:23 Yeah.

Dan Lieberman 1:00:23 Yeah. This is a, this is an important message that the whole world needs to, to know.

Dr. Rangan Chatterjee 1:00:27 In terms of walking, um, there's a, you know, maxim, isn't there, that we should aim to have around 10,000 steps per day. What's your take on that?

Dan Lieberman 1:00:38 [laughs] Oh, well, you know, that's a kind of a funny story. I'm not sure if you've covered that on, this on your podcast before. But, you know, that 10,000 steps a day came from, there was this, uh, accelerometer that was created for the, in Japan just before the Olympics, uh, in '64. And I pa- The story is that apparently in this company, they were sitting around the table deciding what to call it and, and apparently 10,000 is an auspicious number in Japanese. And they said, "Well, let's call it the 10,000 step meter."

Dr. Rangan Chatterjee 1:01:06 Mm.

Dan Lieberman 1:01:06 And turns out it's actually not that bad, right? It's a, it's a, you know-

Dr. Rangan Chatterjee 1:01:12 Not bad-

Dan Lieberman 1:01:12 Yeah

Dr. Rangan Chatterjee 1:01:12 ... as a recommendation, I think.

Dan Lieberman 1:01:13 I mean, you know, it turns out to be okay. Um, so if, if that's a, if that'll help you get more steps in, so, you know, y- if you have one of those watches that makes sure you get 10,000 steps-

Dr. Rangan Chatterjee 1:01:22 Yeah

Dan Lieberman 1:01:22 ... every day, fine. But, but we've, again, uh, w- we've kind of medicalized it, right? We've turned it into a prescription.

Dr. Rangan Chatterjee 1:01:30 Mm-hmm.

Dan Lieberman 1:01:31 And we often talk about optimizing health or whatever. Well, it doesn't work that way, right? Um, if you, if you look at... So, uh, my colleague I- Iman Ley at Harvard has done a lot of work on step counts and health. And if you look at some of the graphs that she's published, for example, first of all, there's a lot of error around the mean, but if you're interested in, say, heart disease, the more steps you take, the better. 3,000 steps is better than 0 thousand steps, and 5,000 steps is better than 3,000 steps, and 7,000 steps is better, et cetera, et cetera, et cetera.

Dr. Rangan Chatterjee 1:02:01 Is there an upper limit?

Dan Lieberman 1:02:03 So far, I don't think she sees a limit. It... for, this is for steps, so just walking, right?

Dr. Rangan Chatterjee 1:02:06 So, like, if you could get to-

Dan Lieberman 1:02:07 No, the line-

Dr. Rangan Chatterjee 1:02:08 ... 15,000 or 20,000 steps, it's, currently from what we know, that's, we think that's gonna help decrease your risk of heart disease.

Dan Lieberman 1:02:14 That's what, that's what her data show.

Dr. Rangan Chatterjee 1:02:16 Okay.

Dan Lieberman 1:02:16 But again, there's a lot of error, variation around the mean.

Dr. Rangan Chatterjee 1:02:18 Sure.

Dan Lieberman 1:02:18 So what hap- what your benefit might not be the same as my benefit, right?

Dr. Rangan Chatterjee 1:02:21 Of course.

Dan Lieberman 1:02:22 There's a lot of variance around that mean. But if you look at the, the data on step counts and, say, all-cause mortality, hmm, it kind of evens out starting around 7,000 steps.

Dr. Rangan Chatterjee 1:02:33 So once you're hitting 7,000 steps a day, it's kinda like, look, you've got most of the benefit.

Dan Lieberman 1:02:38 Yeah. And if you did diabetes, you'd get a different curve, et cetera, et cetera. But again, there's a, there's a mean, but there's also incredible variance around the mean. So what might be good for you is not gonna be the same thing as for me-

Dr. Rangan Chatterjee 1:02:50 Yeah

Dan Lieberman 1:02:50 ... or f- if you're 50 versus if you're 20, or if you've had knee injury, or I could go on, right?

Dr. Rangan Chatterjee 1:02:56 Mm-hmm.

Dan Lieberman 1:02:56 So we prescribe it like, you know, how many aspirin you should take or how many-

Dr. Rangan Chatterjee 1:02:59 Yeah

Dan Lieberman 1:02:59 ... milligrams of such and such you should take, and it doesn't work that way, right? Um, so maybe that helps some people, but I think other people, it makes them confused and agitated and, and, and stressed, right? It's a, it's yet another source of stress in their life.

Dr. Rangan Chatterjee 1:03:12 To make sure you're taking action after watching this video, I've created a free guide to help you build healthy habits. We can all make short-term change, but can those changes become a fundamental part of our life? Often they don't, and that's why in this free guide, I share with you the six crucial steps you need to take. They're really, really effective. If you wanna get hold of that free guide right now, all you have to do is click the link in the description box below. Did, did you say before that, um, some of these hunter-gatherer populations that you have, uh, studied, th- they're taking, what, 15 to 20,000 steps a day-

Dan Lieberman 1:03:52 That's correct

Dr. Rangan Chatterjee 1:03:52 ... ish?

Dan Lieberman 1:03:53 Yeah. But that, but again, that doesn't mean that that's best for them, right? Just because hunter-gatherers do something doesn't mean we should do it. It's not a prescription, right? Hunter-gatherers also don't brush their teeth. Hunter-gatherers don't sleep on nice mattresses. Sh- are you gonna give up your, your, your, your mattress, right, and sleep on the ground? Hunter-gatherers don't g- get on airplanes. Hunter-gatherers don't have refrigerators. Hunter-gatherers don't use vaccines. Hunter-ga- I mean, I could go on, right? So the, the... Uh, we call this a paleo fantasy, the idea that, that what hunter-gatherers do is a prescription for modern life, ri- Instead, it's that by studying h- hunter-gatherers and also farmers, most of my work I do actually with subsistence farmers. So subsistence farmers are people who tend to have no machines. They have, don't have... to do their work, for they have, don't have tractors, they don't have generators-

Dr. Rangan Chatterjee 1:04:39 Okay

Dan Lieberman 1:04:39 ... they don't have electricity, they don't have running water. So these are people who are, who are growing the food that they subsist on, so that's why we call them subsistence farmers.

Dr. Rangan Chatterjee 1:04:46 And, and where, which country are you studying these populations in?

Dan Lieberman 1:04:49 We've studied them in Mexico, we've studied them in Rwanda, we've studied them in Kenya. Uh-

Dr. Rangan Chatterjee 1:04:53 Okay

Dan Lieberman 1:04:53 ... that's where the f- the, the three main places we've done-

Dr. Rangan Chatterjee 1:04:55 Okay

Dan Lieberman 1:04:55 ... this kind of work. Anyway, so just because hunter-gatherers take X number of steps per day doesn't mean that's the number of steps you should take-

Dr. Rangan Chatterjee 1:05:03 Yeah

Dan Lieberman 1:05:03 ... right? Just because hunter-gatherers eat something doesn't mean that's what you should eat. Just because hunter-gatherers don't do something doesn't mean you shouldn't do it either. Instead, these are populations that tell us about the normal range of human variation-

Dr. Rangan Chatterjee 1:05:16 Mm-hmm

Dan Lieberman 1:05:16 ... and, and how our world has changed, enabling us to now understand what's a mismatch, right? What, what is it that we're not adapted for, right?

Dr. Rangan Chatterjee 1:05:24 Mm-hmm.

Dan Lieberman 1:05:24 Because a mismatch disease is a disease that is more common or more severe because our bodies are inadequately or imperfectly adapted for this novel environment. And so these are ways of helping us identify the mismatches in our world, and then, and then addressing them. So, so there is no one number of steps to take per day. The, look, the evidence on exercise is pretty darn clear, right? Which is that... Or physical activity, I should say, right? If anything is better than nothing [chuckles] , right? If you're, if you're completely sedentary, just taking a few steps, you know, more steps a day-

Dr. Rangan Chatterjee 1:05:59 Mm-hmm

Dan Lieberman 1:05:59 ... climbing the stairs, you know, parking your car further away from the shopping ... Anything is better than nothing. More is better, and at a certain point, the benefits seem to tail off, right? Um, and, and, but trying to come up with a number-

Dr. Rangan Chatterjee 1:06:14 Yeah

Dan Lieberman 1:06:14 ... a- an optimum is not only impossible, I think it actually sends an incorrect message, right? That, that, that, that it's like a, like a medicine which you can prescribe in a particular dose. It just doesn't work that way, and I, and I think, uh, and we also get this idea it's like this, this magic pill, right? I mean, exercise is good for you. There's no question about it. Physical activity is good for you because if you don't do it, it's bad for you. But it, it won't prevent all disease. It decreases your vulnerability.

Dr. Rangan Chatterjee 1:06:43 Mm-hmm.

Dan Lieberman 1:06:43 So physic- people who are physically active are much less likely to get breast cancer and, and many other kinds of cancer. Colon cancer. The list is very long. They're much less likely to get heart disease. They're much less likely to get diabetes. They're much less likely to get COVID, right? But, um, um, but, but they're not prevented from getting them. You can still get diabetes if you exercise. You can still get heart disease if you exercise. You can still get-

Dr. Rangan Chatterjee 1:07:05 Yeah

Dan Lieberman 1:07:05 ... all these diseases if you... It, it-

Dr. Rangan Chatterjee 1:07:06 It's about reducing risk.

Dan Lieberman 1:07:07 It reduces your risk. Your, I would say it reduces your... That's the medical term. It, the evolutionary term is it reduces your vulnerability. Right. Your, your, your vulnerability.

Dr. Rangan Chatterjee 1:07:16 Yeah.

Dan Lieberman 1:07:17 So risk is a, is a, is a statistical meas- me- measure, but it's, it doesn't really work that way for, for you and me.

Dr. Rangan Chatterjee 1:07:22 Yeah.

Dr. Rangan Chatterjee 1:07:24 Many people are becoming aware these days of the importance of strength and lean muscle mass, particularly as they're getting older. I think that certainly is a public health message, at le- [laughs] at least in the online podcast world, it's getting out there that it's important. [laughs]

Dan Lieberman 1:07:40 It's incredibly important.

Dr. Rangan Chatterjee 1:07:42 Yeah. So can you explain why you think it's so important based upon what you've seen?

Dan Lieberman 1:07:46 So one of the... You know, as people live l- longer, right? Actually, we're not living all that much longer. The data for h- the hunter-gatherers, by the way, is that if they survive childhood, their mean age of mortality, of death, is between about 68 and 78. 78, by the way, is the life expectancy of Americans today, right? So-

Dr. Rangan Chatterjee 1:08:07 So it's not dissimilar.

Dan Lieberman 1:08:09 No. They're... It's pretty similar, right? But the difference is that they're not getting a lot of these chronic diseases that we get today in, in the Western world, right?

Dr. Rangan Chatterjee 1:08:17 So they may be liv- living to similar ages, but free from these afflictions that, that, that, you know, that reduce quality of life for so many people these days.

Dan Lieberman 1:08:26 Right. And the term we use is health span, right? So health span is the number of years you live without any serious disease or disability, right?

Dr. Rangan Chatterjee 1:08:33 Mm.

Dan Lieberman 1:08:34 And so their health span is basically the same as their lifespan, 'cause there's no medicine to keep them going, right? You know, once they get sick, they die, right?

Dr. Rangan Chatterjee 1:08:41 Mm.

Dan Lieberman 1:08:42 So we evolved to have a long health span, which means therefore to have a long lifespan. And, um, and one of the ways to extend your health span is to stay strong. What, what happens is that, you know, people, if they... You know, muscles are a use it or lose it tissue, right?

Dr. Rangan Chatterjee 1:08:58 Yeah.

Dan Lieberman 1:08:59 They're metabolically expensive. About... Well, you're, you're, you're clearly stronger than I am, but... So most people are about 30 to 40% muscle.

Dr. Rangan Chatterjee 1:09:07 Mm.

Dan Lieberman 1:09:07 People who do a lot of weights might be a little bit higher, right? But muscle's really expensive tissue. You have to eat a lot more calories per day because of all your muscle, right? We get... To, to pay for that, that extra muscle. So we evolved to u- to have muscle when we need it. So when you exercise, you know, do, do strength training exercise, you build up muscle. We also l- evolved to lose it when we don't need it, because it's energy that could go towards something else. Reproduction is what e- evolution cares about. So that's why w- it's a use it or lose it system. So as people become less active in, in, in high-income countries because they've got electric can openers and, you know, running water and l- elevator lifts, you know, they don't have to carry anything. Go to the supermarket, you have a shopping cart instead of carrying the food around, et cetera.

Dr. Rangan Chatterjee 1:09:50 Yeah.

Dan Lieberman 1:09:50 We have prams for the, for the carrying your children, right? I could go on, right? Uh, w- because we don't do any, much strength anymore, we're losing... We lose muscle rapidly as we age.

Dr. Rangan Chatterjee 1:10:01 Mm.

Dan Lieberman 1:10:01 And that creates a condition that you know only too well called sarcopenia.

Dr. Rangan Chatterjee 1:10:06 Yeah.

Dan Lieberman 1:10:06 That's a medical jargon, but it's a good one because sarco is the Greek word for flesh, and penia is loss. So it's flesh loss. I love the term.

Dr. Rangan Chatterjee 1:10:14 [laughs]

Dan Lieberman 1:10:14 'Cause it really makes you think about it, right?

Dr. Rangan Chatterjee 1:10:16 Yeah.

Dan Lieberman 1:10:16 So people become sarcopenic, they, they lose muscle mass, and that sets in motion a vicious circle. Because when you're frail from h- loss of muscle, you suddenly lose the ability to do all kinds of things like get out of a chair, right? Or, or it gets harder and harder because you lose power, you lose strength, and, and that... And then you end up doing less of other things, and it sets in motion this, again, this vicious circle that makes you less and less active, which then sets in motion all kinds of other-

Dr. Rangan Chatterjee 1:10:44 Yeah

Dan Lieberman 1:10:44 ... consequences of physical inactivity. So healthy aging requires you to re- maintain your strength. It's really important.

Dr. Rangan Chatterjee 1:10:51 And the populations that you study, you mentioned before how grandfathers and grandmothers stay remarkably active compared to modern Western populations. They're not specifically doing, you know, [laughs] they're not doing their cardio and then their strength training and then their high-intensity training, are they? They're sort of... H- How have you seen that them maintaining their strength as they age?

Dan Lieberman 1:11:14 Well, well, we're trying to measure that now.

Dr. Rangan Chatterjee 1:11:15 Okay.

Dan Lieberman 1:11:15 There's actually very few studies of this. So there's some grip strength studies out there, right? 'Cause that's easy to measure. And yes, their grip strength stays pretty good. And grip strength is not bad. It's kind of a reasonable proxy for overall strength. Um, but we're, we're actually trying to study this phenomenon more carefully with, with more, with sensors from, you know, looking at other aspects of the body.

Dr. Rangan Chatterjee 1:11:34 Right.

Dan Lieberman 1:11:34 But, uh, but yeah, I mean, there's no question. They stay pretty strong as they live, as they, as they age, and that strength, of course, helps them age better. And, and but the mismatch... And again, because it's a u- it's a use it or lose it system. So if they're using it, so they're not losing it, or they're not losing it as fast.

Dr. Rangan Chatterjee 1:11:49 Mm.

Dan Lieberman 1:11:49 I mean, they're, they're still, they're still, you know, aging, and they're not as strong in their 70s and 80s as they were in their 30s, right? But they're still, they, as far as we can tell, generally a lot stronger than, than the average, you know, American in their 70s or 80s. And, um, and so that's helping maintain their health span.

Dr. Rangan Chatterjee 1:12:12 Yeah. I've often thought about the cost of muscle. And yes, we talk about maintaining strength and putting on muscle. You don't, though, need to become a bodybuilder and have, right, massively huge muscles. If you want to, nothing against that. I'm just saying that's not necessarily what we're talking about. The cost of muscle, like if you're out and energy and food is scarce, and you don't have big refrigerators and freezers and store cupboards with loads of foods. If you put on loads and loads of muscle, you have to feed that muscle, which means you have to acquire more and more foods. So I was thinking it's quite costly muscle, isn't it, to have it on your body?

Dan Lieberman 1:12:57 Very. Yeah. So and you also need extra protein and all that. So, so yeah, we evolved to be, we, we evolved to be e- economical, right?

Dr. Rangan Chatterjee 1:13:05 Mm.

Dan Lieberman 1:13:05 And by that, I mean to have enough, but not too much, right? So you want enough muscle so that you can... And you want, also, you want varied muscle, right? We have muscle fibers that are good for endurance, but they don't produce a lot of power. Those are the slow twitch fibers. And we have muscles that are good for power and, and, and speed, but they're, they're not good for endurance. The-

Dr. Rangan Chatterjee 1:13:25 Mm

Dan Lieberman 1:13:25 ... and those are the type, you know, they're the fast twitch. Then we have the kind of intermediate muscle fiber types. And you need a good mix, right?

Dr. Rangan Chatterjee 1:13:30 Mm.

Dan Lieberman 1:13:30 You need m- mostly slow twitch for aerobic long distance endurance, for the walking and the running, et cetera. But you also need some fast twitch muscles too, right?

Dr. Rangan Chatterjee 1:13:39 Mm.

Dan Lieberman 1:13:39 And, and, um, and you also want to wire up your- ... nervous system to your muscles kind of properly

Dr. Rangan Chatterjee 1:13:45 Mm

Dan Lieberman 1:13:46 And one of the things that physical activity does, exercise, sports, training, all that does is that you learn that you can actually turn on more muscle fibers with your, with a nerve than, than, than before. You can train your nervous system to be more efficient in how you use your muscles. It's all k- it's all a kind of a mix. But, but, but again, you're quite right. You know, body, you know, bodybuilding, that kind of stuff is actually deleterious, right? Having more muscle than you need is actually a cost. Everything's a trade-off, right? So, so too much muscle is actually a problem, as is too little. There's a balance, right?

Dr. Rangan Chatterjee 1:14:18 Is too much muscle only a problem when you can't feed it with enough calories?

Dan Lieberman 1:14:26 That's right, yeah. So at, but ... Which is, which was n- n- normal until very, very recently.

Dr. Rangan Chatterjee 1:14:30 Yeah. So let- let's say you-

Dan Lieberman 1:14:31 So I tend to think in evolutionary terms. Yeah

Dr. Rangan Chatterjee 1:14:33 Yeah. So, so, you know, one of the things a lot of the longevity movement is kind of trying to educate people on is this idea that you, you know, your, your muscle mass is going to go down after the age of 30 unless you do something significant about it, okay? If you're not paying attention and doing something, it's gonna start declining. Can you slow down the rate of decline?

Dan Lieberman 1:14:53 Yeah. And the good news, it's easy. You just, just do weights a few times a week.

Dr. Rangan Chatterjee 1:14:57 Yeah.

Dan Lieberman 1:14:57 You don't have to do that much.

Dr. Rangan Chatterjee 1:14:58 But-

Dan Lieberman 1:14:59 [laughs]

Dr. Rangan Chatterjee 1:14:59 ... I guess-

Dan Lieberman 1:15:00 [laughs]

Dr. Rangan Chatterjee 1:15:01 ... let's say you, you, you go and really, really take this to heart and go, "Right, I'm gonna put on loads and loads of muscle." I was thinking, you know, every time you eat food, depending on what you eat, there is some sort of, uh, cost to the body. There's a, there, there is a, uh, bolus of inflammation to a certain degree, which your, your body has to manage, right? So then-

Dan Lieberman 1:15:23 Yeah. You're also turning on anabolism and catabolism. You're, you know, I'm sorry those are jargon, but you're, you're, you're going back and forth between building tissue and d- and using energy and, and, and, and yeah, it's complicated

Dr. Rangan Chatterjee 1:15:34 Yeah. So, so I kind of think g- g- 'cause I feel we can, you know, as you mentioned, you, you published this paper in Nature in 2010 on, um, minimalist, uh, shoes or, or barefoot walking and running, right? And then people take it to an extreme, and they start trying to do marathons in barefoot shoes-

Dan Lieberman 1:15:50 [laughs]

Dr. Rangan Chatterjee 1:15:50 ... having never been in them before, right? I guess what I'm trying to get to is are we potentially at risk of taking the message ... I've gotta be very careful how I phrase this because sarcopenia is real, and it's causing a lot of problems. So clearly it's better for people to focus on putting on muscle. But are there some people who perhaps are overdoing it and therefore having to overeat and turn on all those mechanisms every time they eat, which potentially could become-

Dan Lieberman 1:16:19 Yeah

Dr. Rangan Chatterjee 1:16:19 ... problematic for their longevity?

Dan Lieberman 1:16:20 Yeah.

Dr. Rangan Chatterjee 1:16:20 It's a, it's a hypothetical point.

Dan Lieberman 1:16:22 I think it's a really interesting hypothesis. I don't know any data on it.

Dr. Rangan Chatterjee 1:16:24 Mm-hmm.

Dan Lieberman 1:16:25 Um, certainly in terms of the endurance part, there are data on that, right? I've seen data on people who do ultramarathons, and, you know, the question is, can you exercise too much?

Dr. Rangan Chatterjee 1:16:33 And can you?

Dan Lieberman 1:16:33 And most of, and most of that study is on, on aerobic exercise, right? Cardio. And the answer is, uh, so far there's very little evidence that you can, right? There's, there was actually a study done here in the UK on the bio- UK Biobank study-

Dr. Rangan Chatterjee 1:16:45 Right

Dan Lieberman 1:16:45 ... where they actually looked at, you know, a few people in the Biobank who did crazy ultra stuff, right? Now, remember, these are very small numbers, right? So the statistics aren't great, 'cause there are not that many people who do ultramarathons. Um, even though it's a growing sport, it's still, you know, a tiny fraction of the population. But so far, there's really no good compelling evidence that they're, they're doing themselves any harm in terms of their lifespan and stuff like that. I've not seen data on, um, on bodybuilding. But there is one trade-off that is, I think, very important and worth discussing, which is that people who do only strength training and don't do cardio. So, so this is something that we've published on, my colleagues-

Dr. Rangan Chatterjee 1:17:22 Mm

Dan Lieberman 1:17:22 ... Aaron Baggish and Rob Shave and I, 'cause our cardiovascular system's evolved. There is a trade-off in the, in how your heart works. So your heart's a pump, right?

Dr. Rangan Chatterjee 1:17:30 Mm.

Dan Lieberman 1:17:31 And it's pumping blood throughout your body. Um, and sometimes when you're doing cardio, what you're trying to maximize is this cardiac output, how much blood you're-

Dr. Rangan Chatterjee 1:17:41 Mm

Dan Lieberman 1:17:41 ... sending through your body at any one given time. So each, each time your heart pumps, how much blood is leaving the ventricle, the heart, right? And f- and then flowing throughout your body, right? That's your cardiac output. And for cardio, that's what you're doing. You're trying to increase cardiac output. When I'm lifting weights, now I'm doing something very different. Now I'm, my heart is pushing ... It doesn't, I don't need as much energy-

Dr. Rangan Chatterjee 1:18:01 Mm

Dan Lieberman 1:18:01 ... from my body, but it's now pushing that blood, uh, through a v- through muscles that are contracting, lots of muscles that are contracting, and that's, and that's high pressure.

Dr. Rangan Chatterjee 1:18:11 Mm.

Dan Lieberman 1:18:11 Right? So that's what we call a resistance or, or a pressure challenge. So when you're doing cardio, it's a volume challenge. But when you're doing weights, it's called a resistance challenge.

Dr. Rangan Chatterjee 1:18:21 Okay.

Dan Lieberman 1:18:21 And that's a ... And that's, some of that's good, right? But pe- but our cardiovascular system's evolved s- such that if we don't engage in cardio, we don't develop, we don't fight the, the kinds of problems that occur in our arterial system that cause hypertension, that prevent us from having cardiovascular disease. And resistance physical activity, which is fine, strength training is good, but if strength training in the absence of cardio s- leads to hearts and cardiovascular systems that don't get that benefit. So-

Dr. Rangan Chatterjee 1:18:57 Wow

Dan Lieberman 1:18:57 ... so, so people who do strength training, fine, but don't skip the cardio. You need both.

Dr. Rangan Chatterjee 1:19:03 And what do you mean by cardio?

Dan Lieberman 1:19:05 E- Cardio is any kind of physical activity that, that, that, that requires you to increase your volume, cardi- your, your, your, your, your output. So swimming, walking, running, volleyball, game of soccer, all that.

Dr. Rangan Chatterjee 1:19:18 Yeah.

Dan Lieberman 1:19:18 And some, some sports are mixed, like s- rowing, for example. I've, I've got a ... I just recently bought a rowing machine, and I absolutely love it. It's, like, my favorite new form of cross-training, right? Rowing is kind of a mix of both aerobic, but also-

Dr. Rangan Chatterjee 1:19:30 Yeah

Dan Lieberman 1:19:30 ... there's some strength involved, right? Uh, that's one of the reasons why I love it. So if y- There's a famous study that was done on Finnish athletes. So Finland's one of those countries where they have fantastic national healthcare system.

Dr. Rangan Chatterjee 1:19:40 Yeah.

Dan Lieberman 1:19:41 And they have data on everybody in the whole country. And they looked at the, um, uh, aging of Finnish athletes who were strength athletes- Versus, you know, weightlifters, versus like cross-country skiers and runners. Finland is famous for both, obviously. Uh, versus the average everyday Fins, right? And it turns out that the, um, that the, the weightlifters who didn't do much cardio actually had as worse, h- or sometimes worse health outcomes as sedentary Fins. They weren't getting the benefit of the cardio that the aerobic athletes, the, the, the endurance athletes were getting.

Dr. Rangan Chatterjee 1:20:19 Wow.

Dan Lieberman 1:20:19 And, and there are, and there are other stu- studies which kind of showed the same thing. So again, nothing wrong with strength training, but don't... The trade-off is don't only do strength training and not do some cardio. You need to do both.

Dr. Rangan Chatterjee 1:20:30 And then, then I think looking back to what you've been saying throughout this conversation, the case you make in Exercised, like we've evolved to, to move every day, right? We- we've evolved to, as you say, these populations walking 15 to 20,000 steps a day. Again, you've made the point, it doesn't mean that we have to do that same level, but it's hard to think that we can get away without doing some degree of kind of walking, significant walking every day. And certainly if I, if I just reflect on, you know, you look at things through the lens of evolution. I look at things through the lens of what have I seen in practice over two decades? And, you know, yes, the research supports this, but time and time again, like, you know [laughs] , the people who do well from a whole variety of different, uh, conditions, whether they be physical health or mental wellbeing, you know, a commonality is that they're moving regularly. And if they're not, increasing it makes a big difference. I've seen it time and time again. And so that's-

Dan Lieberman 1:21:40 And evolution explains why.

Dr. Rangan Chatterjee 1:21:41 And evolution explains why.

Dan Lieberman 1:21:42 So, so you have the data on, and the, and the experience, but you know, we have this old, this famous expression, you know, nothing makes sense in biology except in the light of evolution. You could actually say nothing makes sense except in the light-

Dr. Rangan Chatterjee 1:21:52 Yeah

Dan Lieberman 1:21:52 ... of evolution. And so it's the evolutionary story which explains why this is the case.

Dr. Rangan Chatterjee 1:21:56 Yeah.

Dan Lieberman 1:21:56 And I think that the evolutionary perspective also helps us think creatively about it too.

Dr. Rangan Chatterjee 1:22:02 Yeah.

Dr. Rangan Chatterjee 1:22:03 You mentioned about is there an upper limit to exercise and, um, that some of this data on ultra-marathon runners doesn't appear to suggest that there is, from that data at least. And you've, you, you acknowledge that they're small sample sizes. But again, just, just as with sitting where you said yes, although, um, the Hadza tribe are sitting, you know, similar amounts to what we are sitting each day, the way in which they're sitting is fundamentally different. You can make the same case when we're trying to study exercise and, you know, you know, are marathons harmful, right? For example, if someone was to pose that question. 'Cause some people have, saying, you know, a marathon's too much, right? But the point I'm trying to make is that, let's say, what does running a marathon mean? Well, it means you're completing 26.2 miles, okay? You can do that in a variety of different ways. You can be hell for leather the whole time. You may struggle, but you could be [laughs] in one of those top heart rate zones, or you could be doing it in a very, um, you could in theory do it in a, in a low cardiac, uh, sort of fitness zone under your lactate threshold where you're probably putting, uh, minimal stress on your body or at least less stress. So we c- although both people have completed a marathon, you could make the case that, well, the impact on their body's gonna be completely different because of how they've done it.

Dan Lieberman 1:23:25 Absolutely. You know what? I've run a lot of marathons, right? And I can tell you it's so much more fun to be at the end of the pack, right? The guys who are, you know, and the women who are like trying to win, right? They're not having any fun at all.

Dr. Rangan Chatterjee 1:23:36 Yeah.

Dan Lieberman 1:23:36 They're looking at their watches all the time. They're looking at their splits.

Dr. Rangan Chatterjee 1:23:38 They're pushing it.

Dan Lieberman 1:23:38 They're worrying about, they're worrying about their gels and their hydration, and this, that and the other. They're... You know what? If you're just like running to finish it c- maybe 'cause you're running for a charity, 'cause it gives you a purpose, which I think is also a wonderful thing about the modern marathon. I mean, the London Marathon is the biggest single day charity event in the world.

Dr. Rangan Chatterjee 1:23:54 Yeah. I know.

Dan Lieberman 1:23:54 It is a wonderful party. I've been to it twice. It's just amazing, right? See these people are having a great time, and you watch the guys at the beginning and the women at the beginning walk across the finish line, 'cause I've also sat at the finish line.

Dr. Rangan Chatterjee 1:24:05 Yeah.

Dan Lieberman 1:24:05 They're stone-faced. They're like, you know, they're just relieved. They're like, ah.

Dr. Rangan Chatterjee 1:24:08 Yeah.

Dan Lieberman 1:24:08 They did it. You watch the, the charity runners that come in and they're just, they're the happiest people on the planet, right? They're-

Dr. Rangan Chatterjee 1:24:14 Yeah. It's gonna have a different impact

Dan Lieberman 1:24:15 ... they're, they're having a great time, and they've, they did it. They made it. Now, now, now does, is the, the, the more fundamental question is, is the, do you need to run a marathon to get those health benefits? And the answer is most definitely not.

Dr. Rangan Chatterjee 1:24:26 Yeah. Agreed.

Dan Lieberman 1:24:27 Ma- [laughs] marathons are, are, are a challenge. That's why they're, that's why they're such a big deal. It's hard to run, and to, the training is really the hard part, right?

Dr. Rangan Chatterjee 1:24:34 Mm-hmm.

Dan Lieberman 1:24:34 Training to run 26.2 mile. And it does put a toll on your body. You have this, you know, cardiac troponin breakdown, and I could go on, all the technol- you know, the technical details. Yeah, it's a stress on your body. Um, but you know, it's, there's no evidence that it's bad for you. But do you need to do it? Absolutely not. And I think we have this idea that you have to swim the English Channel or run a marathon-

Dr. Rangan Chatterjee 1:24:54 Mm

Dan Lieberman 1:24:54 ... or do a full triathlon, you know, Ironman, et cetera. Um, absolutely not necessary. Again, some exercise is better than none. More is generally better, but it, the benefits tail off.

Dr. Rangan Chatterjee 1:25:05 Yeah.

Dan Lieberman 1:25:06 And I, and there's always a trade-off. And the, I think the biggest trade-off for like marathons or triathlons is the toll on your family, right? [laughs] You know? All that time out training was, you know, time that you don't spend with your loved ones or, or whatever.

Dr. Rangan Chatterjee 1:25:19 Mm.

Dan Lieberman 1:25:19 Uh, so there, there can be, you know, everything has a trade-off.

Dr. Rangan Chatterjee 1:25:22 Yeah.

Dan Lieberman 1:25:23 And, and, and, and extreme endurance sports are no exception.

Dr. Rangan Chatterjee 1:25:26 Let's talk about another mismatch disease, uh, cancer. You call this a mismatch disease, and you specifically say that it's a disease of high energy.

Dan Lieberman 1:25:36 Hmm. This is important.

Dr. Rangan Chatterjee 1:25:37 What do you mean by that?

Dan Lieberman 1:25:38 So cancers are... So I'm an evolutionary biologist, right? So I think of cancer from an evolutionary perspective, and for me, cancers are a kind of evolution that's gone wrong in the body. It's a kind of natural selection when a s- group of cells suddenly ... acquires a set of mutations, more than one-

Dr. Rangan Chatterjee 1:25:56 Mm-hmm

Dan Lieberman 1:25:57 ... that now enable them to out-compete other cells. They don't turn themselves off. They take a- they, they, they take energy from other cells.

Dr. Rangan Chatterjee 1:26:04 Mm-hmm.

Dan Lieberman 1:26:04 They're now competing with the other cells in your body. It's a form of natural selection in the body that doesn't benefit the host, but it's benefiting those particular cells. And what is it that makes those cells able to do that, right?

Dr. Rangan Chatterjee 1:26:19 Mm-hmm.

Dan Lieberman 1:26:20 Well, it's generally more energy, right? So think about the causes, you know, the, the things that we know are, are, are, are help fight cancer, or the things that we know that cause cancer. Well, high levels of, of body fat, right? People with obesity are much more likely to get cancer. People who have high levels of circulating insulin. Insulin is a, is a hormone that makes things, you know, turns things on. Cancer is about the on switch is off way more than the off switch.

Dr. Rangan Chatterjee 1:26:46 Mm-hmm.

Dan Lieberman 1:26:47 That's basically what's going on. Hormones. Again, hormones like estrogen, progesterone, testosterone, they're turning the on switch on, right? Cancer, the on switch is on so much that these cells are producing molecules that'll cause damage. You get more mutations. They're, they're, they're, they're, um, you know ... I don't know if you've talked about mTOR and rapamycin on the show-

Dr. Rangan Chatterjee 1:27:07 Not really, no

Dan Lieberman 1:27:07 ... really, but, but, but that- that's a- that's the molecular mechanism. That's the off switch, right? So, so, so when we look at populations that move from low-energy environments to high-energy environments, cancer rates go up. Um, and we can see the mechanisms. And, and, and think about physical activity. That turns down cancer rates amazingly. Pe- women who get just basic levels of physical activity, 150 minutes a week, the estimates are there's 30 to 50% lower lifetime risk of breast cancer.

Dr. Rangan Chatterjee 1:27:36 Wow.

Dan Lieberman 1:27:36 Let me say that again. 30 to 50% lower lifetime risk of bre- breast cancer from just basic levels of physical activity.

Dr. Rangan Chatterjee 1:27:45 Wow.

Dan Lieberman 1:27:45 Why don't more of us know this important statistic? Colon cancer, it looks like, like 60% decrease in, in, in, in, in, in incidence rate for people who are more physically active. I could go on, right? And, and that... And why is it? Because physical activity is essentially turning the off switch, right?

Dr. Rangan Chatterjee 1:28:02 But again, flipping it like you did before, yes, technically physical activity is decreasing those levels of cancer. But you could also look at it the other way and go, we've evolved to move. When we, when we don't move, we increase our rate of cancer. [laughs]

Dan Lieberman 1:28:22 Exactly. Exactly.

Dr. Rangan Chatterjee 1:28:22 That's-

Dan Lieberman 1:28:23 I mean, yeah, I mean, that's, that's exactly the ... Y- you're absolutely right. So, so the mismatch is not being physically active. When we're not physically active, our, our... Again, remember what, what's life all about? It's about taking in energy and having babies. So when we have extra energy, our bodies are gonna use that for, for, for building or for, for making babies, for building tissues, for whatever. So we ... You know, so women, for example, who are sedentary, th- they all of a sudden have this extra energy they're not using on physical activity, so what do they do? They increase their estrogen and progesterone levels. Th- those, those experiments were first done by my colleague Peter Ellison at Harvard-

Dr. Rangan Chatterjee 1:28:58 Mm-hmm

Dan Lieberman 1:28:58 ... who showed that women who ran, uh, 20 kilometers a week, so they're spending 180 calories a day, this is not high levels of running, right? Had 50% lower rates of progesterone and estrogen during the second half of the menstrual cycle. Now, these women were not infertile. They were not having trouble con- conceiving. You could say exercise is lowering their progesterone levels. But I would actually say it's the reverse. Being inactive, so the body says-

Dr. Rangan Chatterjee 1:29:24 Yeah

Dan Lieberman 1:29:24 ... "Oh, I've got all this extra energy. I'm gonna shunt that energy towards reproduction."

Dr. Rangan Chatterjee 1:29:29 Yeah.

Dan Lieberman 1:29:30 And because after all, that's what it's all about, right? So, so and now you have the higher levels of estrogen, higher levels of progesterone. Those increase cancer rates. And, uh, physical activity also ... Again, we've talked about repair and maintenance, right? The, the energy that you allocate when you're physically active. After I exercise, right? I, I ran this morning ar- around the Thames. I did probably about eight miles, right? Um, my body's metabolism is still elevated from that morning run for sure. It's probably 3, 4% higher now than it would be if I hadn't gone for that run. And what's that higher metabolism doing? It's not, I'm not replacing the energy [laughs] that I spent running. I'm turning on all kinds of mechanisms throughout my body that are repair and maintenance mechanisms. One of the things I've done is I've increased the number of natural killer cells in my body.

Dr. Rangan Chatterjee 1:30:18 Mm-hmm.

Dan Lieberman 1:30:18 Right? Now, natural killer cells, I love the term, right?

Dr. Rangan Chatterjee 1:30:20 Yeah, me too.

Dan Lieberman 1:30:20 It's very warlike, right? But natural killer cells are a part of our immune system that, um, that are, that are all ... They're swimming around my body all the time, and one of the things they do is they look for cells that have cancer. And they hel- they identify and get rid of cells with cancer. So I've turned up my immune system to help fight, among other things, cancer in my body. But it wasn't that the exercise, you know, was-

Dr. Rangan Chatterjee 1:30:46 Mm.

Dan Lieberman 1:30:47 You ... Again, we evolved to do that, right?

Dr. Rangan Chatterjee 1:30:49 Yeah.

Dan Lieberman 1:30:49 So it's, if ... The, the other way of thinking about it is that not being physically active means that I have a depleted, abnormally low level of natural killer cells, which are swimming around my body right now looking for cells that have cancer. So I, I'm not, I'm, I'm, I'm ... That surveillance mechanism is now turned down. And I could go on. There are many, many other ... You know, a- antioxidants. Uh, you know, your, your ... When you exercise, your, your mitochondria are producing all this energy for your body, but the mitochondria are spewing out what's called reactive oxygen species.

Dr. Rangan Chatterjee 1:31:18 Mm-hmm.

Dan Lieberman 1:31:18 These are mo- these are, uh, molecules with unpaired electrons that can, can ... They c- they, they, they rust. Just like rust is-

Dr. Rangan Chatterjee 1:31:26 Yeah

Dan Lieberman 1:31:26 ... is caused by oxidation, or when your apple, you know, turns brown. That's exactly the same happening in every tissue throughout your body. But of course, exercise isn't bad for us. Physical activity's not bad for us, because our cells are producing antioxidants in abundance.

Dr. Rangan Chatterjee 1:31:40 Mm-hmm.

Dan Lieberman 1:31:41 And but we never p- evolved to turn those antioxidants on as much without being physically active, 'cause we never evolved not to be physically active.

Dr. Rangan Chatterjee 1:31:48 Yeah.

Dan Lieberman 1:31:49 We're turning on enzymes that repair our DNA, another thing that's important for cancer, right? Repairing mutations in our DNA prevents cancer.

Dr. Rangan Chatterjee 1:31:57 Mm-hmm.

Dan Lieberman 1:31:58 Turning on glucagon, which is this hormone that's the opposite of insulin. Ins- high levels of insulin are unquestionably related to cancer. This morning when I ran around the Thames, my glucagon levels went up. Guess what glucagon does? It turns insulin off, right?

Dr. Rangan Chatterjee 1:32:12 Mm-hmm.

Dan Lieberman 1:32:12 So there are all kinds of factors that are involved in physical activity that have to do with energy that decrease the mechanisms that either cause cancer or increase the mechanisms that help prevent or repair the damage that causes cancer.

Dr. Rangan Chatterjee 1:32:29 What about the number of menstrual cycles a woman has?

Dan Lieberman 1:32:32 That's another example. That's, again, it's about energy, right?

Dr. Rangan Chatterjee 1:32:35 Yeah.

Dan Lieberman 1:32:35 Because, uh, menstrual cycles, um, typical in a natural fertility population, wh- which, by which I mean people aren't using, uh, contraceptives, uh, women will get pregnant, then they'll nurse for a long period of time. The nursing, the energy it costs for nursing, keeps their, their, their levels of reproductive hormones down, which prevent them from getting pregnant again until their energy levels get, go back up again.

Dr. Rangan Chatterjee 1:33:02 Yeah, they're not having periods.

Dan Lieberman 1:33:04 That's right. Or, they're not having periods because it's because of energy, right? Now, so a typical woman who's in a natural fertility population will have maybe 150 menstrual cycles in her life. Now, with contraception, um, and fewer offspring, women I think get a, an average about 400-

Dr. Rangan Chatterjee 1:33:26 Yeah

Dan Lieberman 1:33:26 ... menstrual cycles. That's, you know, 250 more big massive pulses of estrogen and progesterone that are, you know, important for reproduction, but there's a trade-off. Everything has a trade-off. They also increase the rates of, of some cancers, including breast cancer.

Dr. Rangan Chatterjee 1:33:42 Yeah, I don't think many people think about things like that. You know, when they're thinking about cancer, they're not thinking about the number of menstrual cycles, right?

Dan Lieberman 1:33:50 Yeah.

Dr. Rangan Chatterjee 1:33:51 You know, 'cause it's fascinating that. You know, 150 versus 400, let's say on average, that is a huge difference-

Dan Lieberman 1:33:59 Yeah

Dr. Rangan Chatterjee 1:33:59 ... you know, over the course of a life.

Dan Lieberman 1:34:01 Yeah, absolutely. Or, or, you know, uh, insulin levels. The people walking around today, like we see in the streets of London, the estimates that we have, or the, the data we have, there's everybody's walking around with higher levels of insulin-

Dr. Rangan Chatterjee 1:34:15 Mm

Dan Lieberman 1:34:15 ... than people who are walking the same streets a few generations ago. It's because we have so much more energy available to us.

Dr. Rangan Chatterjee 1:34:21 Yeah.

Dan Lieberman 1:34:21 We're not going through those cycles of, of positive and negative energy balance. I think that's one of the reasons why intermittent fasting, uh, or, or, you know, reduced, you know, you know, being careful about your caloric intake is beneficial because it's basically keeping those insulin levels down. Also not eating too much sugar and as well. So-

Dr. Rangan Chatterjee 1:34:38 What, what did you see, uh, in relation to fasting in some of these hunter-gatherer or more traditional populations?

Dan Lieberman 1:34:44 Well, they just don't eat all the time. I mean, look, in my building, right, you know, um, there's a snack machine. There's, it, right at the bottom of the stairs, right?

Dr. Rangan Chatterjee 1:34:52 This is in Boston?

Dan Lieberman 1:34:53 Yeah. Uh, my, my building at Harvard, right?

Dr. Rangan Chatterjee 1:34:55 Yeah.

Dan Lieberman 1:34:55 So if I'm, if I'm hungry, and I, I'm, like, a little, you know, I'm working on a paper or, you know, something, you know, or upset by my colleagues or whatever, and I get, you know, I'm stressed. And stress makes you hungry. Cortisol-

Dr. Rangan Chatterjee 1:35:09 Mm

Dan Lieberman 1:35:09 ... it ma- makes you hungry, right? Um, I can just run down to that s- machine and get all kinds of crap, [laughs] right? All kinds of ultra-processed junk, right? Full of sugar and whatever. Um, and, and it satisfies my craving. It's not gonna ... It's gonna make me hungrier later on. But if you're in a subsistence population, or if you're a hunter-gatherer and you're hungry, you have to [laughs] go out and either find the food that you're gonna eat, or if you're a farmer, you have to go and cook it and prepare it and whatever and get it from your, you know, the silo or whatever. You, you, you're just not surrounded by food, and you're not surrounded by high energy food.

Dr. Rangan Chatterjee 1:35:45 So you, you don't see them necessarily practice, um, a form of fasting or restricted eating window, or one day a week where they would reduce their calorie intake. Nothing like that. It was more, it was kind of inbuilt.

Dan Lieberman 1:35:57 They, they have no choice, right? You know what I mean?

Dr. Rangan Chatterjee 1:35:59 Yeah.

Dan Lieberman 1:35:59 Look, if they could eat as much as we do, they would. Absolutely. Uh, when I ... The populations I work with, people are always hungry, and they're always asking for food.

Dr. Rangan Chatterjee 1:36:07 Hey, guys. I really hope you're finding this useful. If you are, and you want more content like it, please do check out my book, Make Change That Lasts: Nine Simple Ways to Break Free From the Habits That Are Holding You Back. It's in all the usual places as a paperback, e-book, and as an audiobook, which I'm narrating. Now, back to the video.

Dan Lieberman 1:36:28 Uh, let me tell you a funny anecdote. Um, so, uh, once I spent about seven or eight days with a group of hunter-gatherers, with, uh, some colleagues.

Dr. Rangan Chatterjee 1:36:36 Where was this?

Dan Lieberman 1:36:37 This is in, in Tanzania. And, um, and we had, you know, we came with a few Jeeps, and you're full of food, et cetera, and we spent a wonderful time with this, these wonderful, these, these folks, and they were very kind and whatever. And the last night we s- we, you know, we thought, "Let's have a party." And we cooked everything that was left that we had. All the food left, 'cause we were just h- heading back to town, right? And so the, we had this cook with us, and he made, you know, he boiled every bit of rice that we had, and he made some cakes, which he smeared with jam, and he had ... I mean, it was like, it was an amazing feast, right? And I've never seen people eat so much. I mean, [laughs] they ... And it was like a paleo diet nightmare.

Dr. Rangan Chatterjee 1:37:17 [laughs]

Dan Lieberman 1:37:18 They ate so much rice and cake and whatever, and they went back for seconds and thirds. There was nothing left at the end, right? Um, why? Because they're hungry. And, and all of a sudden they had this bounty of food, whereas y- you and I might, like, okay-

Dr. Rangan Chatterjee 1:37:31 Yeah

Dan Lieberman 1:37:31 ... I don't need to eat thirds, right? But they, they, they were, they were s- they, they were happy. And then we, they, we danced for hours and hours later, right? But, um, um, you know, when you're in a, if you're in a situation where food is, is always in short supply, you're always gonna eat what's available to you.

Dr. Rangan Chatterjee 1:37:47 Yeah.

Dan Lieberman 1:37:47 But you're only gonna eat the food that is available to you. Like breakfast, right? They often don't have breakfast, not because they're trying to intermittent fast and, you know, trying to, you know, skip a meal so that they can, you know, turn off mTOR, et cetera, et cetera. They're, they're doing it because [laughs] there's no food in camp.

Dr. Rangan Chatterjee 1:38:03 Yeah.

Dan Lieberman 1:38:03 They have to go out and find it.

Dr. Rangan Chatterjee 1:38:05 Yeah. That's ultimately what a lot of these modern practices are about. They're a, they're, for me at least, they're a way of navigating the modern world. That sort of point about energy, which you were talking about in relation to cancer, but there's a, there's a broader point. Many of us are living in a world of energy excess, where, where we're exposed to lots and lots of energy that, if we're not careful, will end up in our mouths [laughs] and on our bodies. And that is why some people, some people don't like the word rules, some people don't like the words, uh, restriction, and I get that, but we're all different. We all need our own strategy to navigate the modern world.

Dan Lieberman 1:38:43 Oh, it's, it's a, it's a-

Dr. Rangan Chatterjee 1:38:44 But-

Dan Lieberman 1:38:44 It's a nightmare. Yeah

Dr. Rangan Chatterjee 1:38:45 ... but some people find something like a time-restricted eating protocol, where they don't eat after 7:00 PM, for example, they find that really helpful 'cause it just stops their evening-

Dan Lieberman 1:38:56 That's great

Dr. Rangan Chatterjee 1:38:57 ... snacking. It may work for them. It may not work for someone else. Um, it's like why some people find a low-carb diet or a low-fat diet, or whatever it might be, useful b- b- because for them, that's their framework which allows them to navigate this modern food environment.

Dan Lieberman 1:39:12 I totally agree.

Dr. Rangan Chatterjee 1:39:13 Whereas last summer I was in Kenya for four weeks, and I was bending the ear off this, this young Maasai [laughs] chap. I was asking, "Can you tell me, what time do you guys eat?" But he said, "Yeah, we'll have m- a bit of meat in the morning at 7:00." I said, "Okay, and then what do you do then?" He says, "We're out with the cattle in the day." And he says, "We don't really eat, but we'll sort of take, you know, if we're hungry, I just snack on some berries or whatever I might come across, and then we'll eat again." I said, "What time?" He says, "Maybe around 7:00 or so when we're back. W- It'll be more meat then." Right? So again, this is one person sharing what he and his tribe do. But it was fascinating for me 'cause I thought, "Well, we kinda talk about this 12-hour window in every 24 hours where we don't eat as a modern way of trying to replicate things, but that's kinda what they're doing-

Dan Lieberman 1:40:00 Yeah

Dr. Rangan Chatterjee 1:40:00 ... naturally."

Dan Lieberman 1:40:01 Well, so the Maasais are, are pastoralists, right? They're, they're, they're herders. And, um, uh, and so they go out for the day and they, you know, especially the, the, the, the men-

Dr. Rangan Chatterjee 1:40:09 Yeah

Dan Lieberman 1:40:09 ... and/or kids as well, watching the, the, the, the animals. Um, hunter-gatherers I've, uh, populations that I've seen but also mostly read about, 'cause of course I've only, you know, [laughs] there's more to read about than to see. Um, they snack constantly. They dig up tubers. They eat them right there in the field.

Dr. Rangan Chatterjee 1:40:28 Mm-hmm.

Dan Lieberman 1:40:28 Right? They're not, they're not saving them all for dinner. Um, guys, I think you read the, the description about those guys who they've s- they've f- you know, when we went out hunting, they failed to hunt that particular day. So what did they do? We went from hive to hive to hive to hive getting honey. They didn't bring a single ounce of honey home back to camp. They ate it all themselves, and thus had a m- massive sugar overdose that day.

Dr. Rangan Chatterjee 1:40:51 I love that. That's the [laughs] it w- it was such beautiful writing. It was so evocative when you went on this hunt with these guys and yeah, I think you talked about, you know, you heard an arrow being pulled, but you came back looking disappointed. The arrow missed. But then the birds helped guide you to all the, all the honey, basically. [laughs]

Dan Lieberman 1:41:09 The honey guides, yeah.

Dr. Rangan Chatterjee 1:41:10 So ju- just so no one's interpreting that as, "Oh, um, my evolutionary ancestors would gorge on honey. Let me go to the supermarket and buy big tubs of honey to gorge on as well."

Dan Lieberman 1:41:25 [laughs]

Dr. Rangan Chatterjee 1:41:25 [laughs] Hopefully no one will do that. But should we just be really clear? You're saying some of them snack quite a lot as well. Is it not then the take home that in an environment of, uh, limited energy, people are gonna snack? They're gonna take honey. They're gonna take whatever they can when it's available. Whereas in an environment of energy surplus, we need to be careful with things like snacking and, and eating late, and that sort of stuff.

Dan Lieberman 1:41:50 Yeah. We have to do something really weird. We have to now not eat the food that's around us.

Dr. Rangan Chatterjee 1:41:55 Yeah.

Dan Lieberman 1:41:56 That never happened for human evolution. Y- you know, I go to the supermarket and it's, you know, I go to a, a buffet. I mean, um, or, you know, when it's somebody's birthday, everybody brings in cake, et cetera, and I have to, I ha- I, I just, you know, before this, I just had to, um, I had, went for a coffee shop with some folks and, and, and all of a sudden there were these, you know, lovely sugary, floury things to eat in front of me that I hadn't ordered, right? And I, I ate one because it's delicious and, you know, it's very hard. You have to work... We have to work... We have to... We actually sometimes pay extra money for food that has less nutrients in it-

Dr. Rangan Chatterjee 1:42:30 Yeah

Dan Lieberman 1:42:30 ... less sugar in it because it's more expensive than the stuff-

Dr. Rangan Chatterjee 1:42:32 That's crazy. No wonder people are struggling

Dan Lieberman 1:42:34 ... I mean, so we have to, we're, we're now in a world where we have to actually do something that's c- fundamentally unnatural, fundamentally against basic instinct, which is to, which is to, to use willpower to not eat the abundance that w- for which we are surrounded, and the abundance is often full of all kinds of toxins and poisons-

Dr. Rangan Chatterjee 1:42:56 Yeah. Uh, uh

Dan Lieberman 1:42:56 ... and whatever. That's, that, I mean, and that is a problem that... And, and then, you know, of course people are gonna struggle, right? And that, that's why it's a problem that's not just an individual issue. This is a social, political, larger question than any one individual.

Dr. Rangan Chatterjee 1:43:11 Yeah.

Dan Lieberman 1:43:11 And we need, we need to help to help ourselves.

Dr. Rangan Chatterjee 1:43:13 This goes back to how we started this conversation about the escalator and how, you know what? It is, you're gonna, it's gonna take a certain type of person to actively choose the stairs when there's an escalator there, right? No blame, no guilt. It's just who we are. Kind of the same thing with food, right? It's like if there's energy-dense tasty food there, all our wiring from a long, long [laughs] time, hundreds of thousands of years, is to eat that food.

Dan Lieberman 1:43:41 M- millions and millions-

Dr. Rangan Chatterjee 1:43:43 Millions

Dan Lieberman 1:43:43 ... and millions and millions and millions of years. Exact- Look, I, I want to take the s- the escalator just as much as everybody else, but do you know why I take the stairs?

Dr. Rangan Chatterjee 1:43:51 I also take the stairs, but go on, give me your reason.

Dan Lieberman 1:43:52 Do you know why? Because if anybody sees me, and I'm this, you know, I've written books on exercise, I'm a hypocrite. The number one reason I take the stairs is not because, you know, 'cause I get l- less exercise, because I'm afraid of being caught out and being kind of, as you were. I'm sorry, it's, it's, it's embarrassing, but it's actually true.

Dr. Rangan Chatterjee 1:44:07 No, no, it's good to be honest. Look, I, I, I, I mean, I, that, that is a partial reason for me as well in this country. But the real point for me is that, again, I'm aware that not everyone likes the word rules, but I feel that I've seen this with, with many patients, I've seen this with myself, that there are certain things that are very helpful. So I have an internal rule that is I always take the stairs unless in exceptional circumstances. That's a rule that I've now internalized. It's the norm for me. That helps me navigate this, uh, this modern world where the temptation is to outsource my movement to electronic things and lifts and escalators and all these contraptions, right? So it means unless I've got an injury or I've got a ton of suitcases and I physically can't do it, or whatever it might be, I will take the stairs.

Dan Lieberman 1:45:01 And that's great.

Dr. Rangan Chatterjee 1:45:02 And that works for me, but I know across the population, that's gonna be very hard to persuade everyone to do.

Dan Lieberman 1:45:08 Yeah. No, no, I, I agree with you. But I think there's another, there's another dimension to this, which is that, yes, we create these rules, we create these ideas or, or, you know, uh, suggestions, but the other thing I was gonna say is that a lot of them are all geared towards weight. A lot of people are told to, to not eat this or do eat this because it'll prevent you from gaining weight or help you lose weight.

Dr. Rangan Chatterjee 1:45:32 Okay.

Dan Lieberman 1:45:32 You know, there's this big debate now about exercise and weight loss, right? And I've, I've heard people say, "Oh, well, you know, actually I don't need... You know, taking the stairs isn't so im- important for me because it's not gonna help me lose weight, so I might as well take the escalator." I've heard this from people, right?

Dr. Rangan Chatterjee 1:45:46 Yeah.

Dan Lieberman 1:45:46 When we're talking about this after burn, right, after the physical activity, the entire literature on, on, on, on how exercise raises your metabolism is primarily about whether or not that extra energy that you burn will help you lose weight. [laughs] You know, uh, not, not, not about all the other benefits-

Dr. Rangan Chatterjee 1:46:02 Yeah

Dan Lieberman 1:46:03 ... that come from, from that elevated metabolism. So by seeing everything through the lens of, of weight loss and weight gain-

Dr. Rangan Chatterjee 1:46:10 Yeah

Dan Lieberman 1:46:10 ... and weight is not health. Weight is related to health, but it is not health. By, by, by tying everything to weight, people forget what the other benefits and importances, the important reasons for being physically active are-

Dr. Rangan Chatterjee 1:46:21 Yeah

Dan Lieberman 1:46:21 ... and/or, or discount, uh, uh, you know, certain activities, uh, because it's all viewed through this, this, you know, weight, weight, weight, weight, weight, weight, weight, weight.

Dr. Rangan Chatterjee 1:46:30 No, I completely agree. I mean, what, what is your take on the exercise and weight loss issue? Which is-

Dan Lieberman 1:46:35 Oh. [laughs]

Dr. Rangan Chatterjee 1:46:35 I mean, it's one of those hot controversial topics. I mean, I'll share my view in a minute, but I'd love to know your perspective.

Dan Lieberman 1:46:41 Well, I, I think one thing is completely uncontroversial, I hope, which is that there's no question that physical activity is crucial in preventing weight gain. Study after study-

Dr. Rangan Chatterjee 1:46:50 Yeah

Dan Lieberman 1:46:50 ... after study after study after study shows that people are more physically active regardless of what they're eating. That actually helps prevent weight gain. And sometimes you'll read, oh yeah, but, you know, physical activity, exercise makes you hungry so you're gonna eat more. That's just been debunked. That's not true. You do eat a little bit more, but you don't eat as much as, as you spend. So, uh, s- I think that's uncontroversial. I- in fact, and we often talk about diet versus exercise for weight loss. That's a strange di- opposition. It should be diet and exercise. Why would you not do the two together, right? Um, although it's, it's harder to exercise, and if you're overweight or have obesity, right, it's like carrying weights on your body, right?

Dr. Rangan Chatterjee 1:47:28 Yeah. It's harder.

Dan Lieberman 1:47:28 It's, it's... You know, walking, a person with obesity walking the same distance as, as somebody without it is, is spending 14% more energy. It's hard, right?

Dr. Rangan Chatterjee 1:47:36 Wow.

Dan Lieberman 1:47:37 It's, it's difficult, right? So, uh, it's, it's challenging. Um, and generally you're unfit and so you get less reward. I think there's also compelling evidence that exercise can help you lose weight, but the, the issue is that it doesn't help you lose a lot of weight rapidly. I think there are, there are careful, well-designed, randomized control perspective studies where they weigh everything going in and weigh everything going out, showing that people who get more than a moderate amount of exercise, you need at least 300 minutes a week. You can and will lose weight, but you're not gonna lose a lot. So if you wanna lose a lot of weight fast, there's no question dieting is better. But if you want to lose some weight-

Dr. Rangan Chatterjee 1:48:15 Yeah

Dan Lieberman 1:48:15 ... there's no question that exercise can help. But it's not gonna be a huge amount. But what it's really gonna help you do is that once you lose that weight, 'cause dieting, the problem with dieting is not that people don't lose weight when they diet. They do. The problem is it comes-

Dr. Rangan Chatterjee 1:48:27 Yeah

Dan Lieberman 1:48:28 ... it comes bouncing back, right? It comes, it comes rebounding, right? And then often you, you're, you're not gaining muscle, you're just gaining fat. And, and so you get this yo-yo effect.

Dr. Rangan Chatterjee 1:48:37 Yeah.

Dan Lieberman 1:48:38 The way to prevent that is to con- to stay exercising, to stay physically active. That has an incredibly important role, and it should be-

Dr. Rangan Chatterjee 1:48:46 Yeah

Dan Lieberman 1:48:46 ... part of every weight, weight strategy.

Dr. Rangan Chatterjee 1:48:48 Yeah. I, I, I, I really, I do agree with that actually, and I think, uh, you know, there's no question that people can lose weight without paying much attention to physical activity or exercise, 'cause I, I've seen it over and over again. People will report that. Of course it's possible, and many people do it, but most people stroke all people who are trying to lose weight are not trying to do it for four to six weeks. They're trying to make it a significant part of their life. They're, they're trying to transform their life. They, they want it to be long-term, not just for January or January, February, or for the, for the wedding or the beach, or whatever it might be, right? They want it beyond that. And this is where I've always had a slight issue with some of these, uh, studies or at least how they're reported. And you, you know, it was all blowing up on YouTube last year in the health sphere on this. Exercise, you know, nothing to do with weight loss, and all this sort of stuff, and it's like, I just, I don't... First of all, I don't see how, how that's that helpful for people. And it, it sort of, it makes things very one-dimensional, yes, about weight when there's so many more benefits. But even if we are talking about weight, let's look at it another way. Whether exercise helps you to, uh, lose weight or not is not just, in my view, about the direct effect on, uh, calories from what you're burning off, right? And let me explain what I mean by that. People who are struggling with their health and are trying to, let's say, lose weight or make changes- There's all kinds of things to tackle. So if their mood is low, they're less likely to go out and move. They're gonna sit at home. They're gonna possibly more likely to comfort eat, binge watch things on TV, uh, accumulate stress, have less optimal sleep, which again, will make them more hungry the following day 'cause of the changes in hormones. So for me, it's like, you know what? If you're someone who can walk 30 minutes a day, whether it directly burns enough calories to justify it for your weight loss plan, it will improve your moods, your self-esteem. It will help you lower stress. You'll feel better about yourself and your place in the world. These are real things for human beings. You cannot just look at it through the lens of how many calories were burned here. That's useful to know, but this is my bias as a-

Dan Lieberman 1:51:08 No, I vigorously agree. I could not agree more

Dr. Rangan Chatterjee 1:51:09 ... having seen-

Dan Lieberman 1:51:10 Yeah, yeah

Dr. Rangan Chatterjee 1:51:10 ... so many patients. Like, you can't just look at one thing. You have to look at the totality of all the inputs into this person's life. And moving more, for most people, makes them feel better. [laughs]

Dan Lieberman 1:51:20 Yeah. And, and it also does have energetic effects too.

Dr. Rangan Chatterjee 1:51:23 Of course it does.

Dan Lieberman 1:51:23 It's both. It's a combination. And, and what we tend to be, you know, again, by l- by looking just through this one lens and, of, of, you know, calories in, calories out, or whatever, we're missing, like, what is it that actually m- m- moves energy around in our bodies?

Dr. Rangan Chatterjee 1:51:37 Yeah.

Dan Lieberman 1:51:37 It's hormones, right? So just as, as one example of what you just said, just one example, right? People who are more physically active have lower basal levels of cortisol. What does cortisol do? It's the, it's the arousal stress hormone.

Dr. Rangan Chatterjee 1:51:48 Yeah.

Dan Lieberman 1:51:49 And guess what? When my cortisol levels go up, like when I'm stressed about, you know, this, that, or the other, I'm more likely to eat.

Dr. Rangan Chatterjee 1:51:55 Yeah.

Dan Lieberman 1:51:55 Yeah. Um, so it's just one of the, of this complicated interconnected integrated system.

Dr. Rangan Chatterjee 1:52:02 And, and chronically elevated cortisol, you know, the primary stress hormone, or you could argue the primary stress hormone, you know, encourages belly fat.

Dan Lieberman 1:52:10 Exactly.

Dr. Rangan Chatterjee 1:52:11 Right?

Dan Lieberman 1:52:11 Yeah.

Dr. Rangan Chatterjee 1:52:11 Rather than subcutaneous fat.

Dan Lieberman 1:52:12 And that's the vis- that's the inflammatory fat.

Dr. Rangan Chatterjee 1:52:14 Yeah. So it's, it's all these things together. I mean, what did you see in some of these populations in, in terms of, uh, I don't know if you measured it or not, but what was your perception of levels of stress in hunter-gatherer populations?

Dan Lieberman 1:52:29 Ooh, good question. First of all, most of the research I've done is on, is on subsistence farmers-

Dr. Rangan Chatterjee 1:52:33 Okay

Dan Lieberman 1:52:33 ... and not hunter-gatherers, but I mean, I've visited hunter-gatherers. But, um, we've never measured that. We've... But there are studies where they look at, again, cor- so cortisol is a complicated hormone in that cortisol doesn't cause stress. Cortisol goes up when you are stressed, right? So people have measured cortisol in some of these populations.

Dr. Rangan Chatterjee 1:52:49 Mm.

Dan Lieberman 1:52:49 And the levels tend to be low, but again, that could be because of physical activity. Um, I don't know of any good studies that measure psychosocial stress-

Dr. Rangan Chatterjee 1:52:56 Mm

Dan Lieberman 1:52:56 ... in any of these populations. Um, and, and I would say that their, you know, their lives are not easy.

Dr. Rangan Chatterjee 1:53:02 No, for sure.

Dan Lieberman 1:53:03 There, there's, just like in our lives, there are problems, right? Um, there are... They're worried about food. There's conflict between individuals. There's, um, you know, climate change. There's all kinds of things-

Dr. Rangan Chatterjee 1:53:17 Mm

Dan Lieberman 1:53:17 ... going on in their world that makes them, like the rest of us, uh, stressed. But I think that their life is slower. Um, you know, they're not, they're not getting a 24/7 news feed. [laughs] They're, you know, there, there is a... I'm certainly calmer when I'm out there, right?

Dr. Rangan Chatterjee 1:53:38 Yeah.

Dan Lieberman 1:53:38 'Cause I'm disconnected from all the crap that's going on normally in my life that can make me aroused and-

Dr. Rangan Chatterjee 1:53:43 Mm-hmm

Dan Lieberman 1:53:43 ... and stressed. And, um, I, I think it's a reasonable hypothesis that just general levels of stress are lower. Not that they're absent. They're not.

Dr. Rangan Chatterjee 1:53:52 No.

Dan Lieberman 1:53:52 These are, these are not, you know, Rousseau's, you know, um, noble savages, right? That's not, that's not what we're seeing. But, um, but I do think that the world we live in today... Look, the average hunter-gatherer, as far as we know, maybe meets 250 people in an entire lifetime. Today, just getting to this studio, I met, I didn't interact with them mostly, but thousands and thousands-

Dr. Rangan Chatterjee 1:54:19 Yeah

Dan Lieberman 1:54:19 ... of people, right? Uh, you know, and some of those, most of those were perfectly harmless interactions. But, um, but you know, there's just... Our, our lives are just intense, right? In this modern, wonderful, crazy, but also stressful environment-

Dr. Rangan Chatterjee 1:54:33 Yeah

Dan Lieberman 1:54:33 ... that we live in today. And you know, I was checking my phone today and, you know, what's the news, et cetera, and all that kind of stuff. And I have to, you know, figure out I have to get to my flight tomorrow, what time, and how do I get to the, you know, whatever. And, you know, I can-

Dr. Rangan Chatterjee 1:54:44 But these, these are real. These are, these are-

Dan Lieberman 1:54:46 Mm.

Dr. Rangan Chatterjee 1:54:47 This era of bombardment of information, whether it be news or emails or flight check-ins or whatever, they're, they're all significant.

Dan Lieberman 1:54:56 Yeah, they add up.

Dr. Rangan Chatterjee 1:54:57 They, they add up.

Dan Lieberman 1:54:58 Absolutely.

Dr. Rangan Chatterjee 1:54:58 Maybe each one in isolation is no biggie, but you put them one after the other, throw a bit of jet lag in for you, and all sorts of... You know, it does add up, doesn't it?

Dan Lieberman 1:55:06 I, I agree. So, so I don't know good data on, on stress levels, but I would be very surprised if-

Dr. Rangan Chatterjee 1:55:11 Okay

Dan Lieberman 1:55:12 ... if, if they weren't lower.

Dr. Rangan Chatterjee 1:55:13 What about sleep? I, I know you bust the eight-hour sleep myth-

Dan Lieberman 1:55:16 Yeah

Dr. Rangan Chatterjee 1:55:16 ... in, in your book. Um, feel free to, to sort of explain that, but, but I'm, I'm really interested as to what sort of... What did you observe in terms of, you know, sleeping patterns and sleeping duration?

Dan Lieberman 1:55:30 So I've never collected data on that, but I've read the literature on that. But my, my impression is [laughs] people just sleep, you know? They, they, you know, when they're tired, they sleep, and when they're not tired, they don't sleep, and, and it's just not a big deal. And it's-

Dr. Rangan Chatterjee 1:55:42 But not... Is it, is it one prolonged go, or is it-

Dan Lieberman 1:55:44 So the literature is... Again, I've never measured this.

Dr. Rangan Chatterjee 1:55:46 Okay, fine.

Dan Lieberman 1:55:46 But, but others have. And, um, in general... So there's a researcher at the University of UCLA who's, who's, who's done a lot of these sleep studies. So he put, um, sleep monitors on three populations, the Hadza, uh, the, the San in the Kalahari, and, um, Ache in, um, the, the Amazon. Uh, there's also studies now from people in Madagascar and, uh, other populations in the world where people aren't-

Dr. Rangan Chatterjee 1:56:17 Mm

Dan Lieberman 1:56:17 ... connected 24/7 to the world. So they have no electricity, so they don't have phones. They have lights, TV, all the things that we're supposedly, uh, uh, robbing us of sleep, right? You know the idea that Ederson was the, was the, was the-

Dr. Rangan Chatterjee 1:56:29 Mm

Dan Lieberman 1:56:29 ... you know, killed sleep, right? Um, they sleep, I think, 6.7 hours in the evening.

Dr. Rangan Chatterjee 1:56:36 Okay.

Dan Lieberman 1:56:36 6.5, I can't remember. They don't get eight hours. They rarely nap. Um, they tend to sleep more when it's cold and a little bit less when it's hot. Um, and, um, and they seem to be just fine. And furthermore, uh, when you look at big epidemiological studies in the West, right? Where you look at hours of sleep on the X axis and some health outcome on the Y axis, like cardiovascular disease or something like that. It's, it's always a U-shaped curve with lots of variation around the mean. And the bottom of that U-shaped curve, i.e. the, the, the, the sleep number, the hours of sleep that are associated with best health is about seven.

Dr. Rangan Chatterjee 1:57:12 Mm.

Dan Lieberman 1:57:13 Not too far off from what our ancestors did, right?

Dr. Rangan Chatterjee 1:57:16 Yeah.

Dan Lieberman 1:57:17 So, so, so-

Dr. Rangan Chatterjee 1:57:18 That's qua- that's quantity though, isn't it? We don't know... Do we... We don't know quality?

Dan Lieberman 1:57:22 No, we have no idea. No. No, it's very hard to measure that.

Dr. Rangan Chatterjee 1:57:25 One of the arguments might be that, um, and, and I've seen this a lot, um, over the years, where on the, on the, on the outside, patients are sleeping, uh, let's say seven, eight hours, but they're still waking up feeling exhausted. There could be many reasons for that, but I've certainly seen enough times where people are, uh, chronically stressed and stimulated in the evening before they go to bed. It may seem as though they're sleeping for the same amount of time, but I, you know, again, I don't have a sleep lab, but it seems very much that the quality of that sleep-

Dan Lieberman 1:58:00 Sure

Dr. Rangan Chatterjee 1:58:00 ... wasn't as significant.

Dan Lieberman 1:58:02 And, and psychosocial stress turns up cortisol.

Dr. Rangan Chatterjee 1:58:05 Yeah.

Dan Lieberman 1:58:05 Cortisol doesn't make you stressed. Cortisol goes up when you are stressed. Cortisol is the arousal hormone. It's the hormone that helps us-

Dr. Rangan Chatterjee 1:58:11 Exactly

Dan Lieberman 1:58:11 ... get energy, again, back to energy, to help us run away from the lion or whatever it is, right? So, so when you, when you fall asleep, right, you go through four different stages-

Dr. Rangan Chatterjee 1:58:20 Mm

Dan Lieberman 1:58:20 ... of non-REM sleep. You slowly, slowly become less and less aware of the wor- outside world, so that first you can hear the outside world-

Dr. Rangan Chatterjee 1:58:28 Mm

Dan Lieberman 1:58:28 ... but et cetera. And then finally you go into this non-REM period, and then you, you cycle back and forth, right? Cortisol slows that. I mean, a- and, and also it prevents you from getting into the non-REM, and you're more in the, in the less serious, you know, you know, the less REM parts of sleep. So, um, so if you're stressed, your sleep is gonna be... is not gonna be as good. I mean-

Dr. Rangan Chatterjee 1:58:51 Yeah

Dan Lieberman 1:58:51 ... and we know that. Um, and it's funny if you think about it. Like I, I... You did ask me about my experiences. I will say one thing about, about sleep in these places. It's bedlam, right? Nobody goes to sleep in a quiet, dark room on a soft mattress with the curtains closed and no sound, and you know. Like think about like how so many of us sleep, right?

Dr. Rangan Chatterjee 1:59:12 Okay.

Dan Lieberman 1:59:12 We're, we're in this like isolation chamber, right? And that's not how it is in any of these camps. There's always somebody up and about. You can hear stuff. You can hear hyenas in the distance. I mean, there's all this stuff going on, right? And, um, it's chaos. Um, and um... But because people aren't bothered by it because that's just normal, right? They, they don't-

Dr. Rangan Chatterjee 1:59:33 Yeah

Dan Lieberman 1:59:33 ... they're not irritated by it. They just fall asleep, right?

Dr. Rangan Chatterjee 1:59:35 Last night.

Dan Lieberman 1:59:36 But we have this like... We get stressed partly because, you know, the neighbor's playing their music, right? Or there's an ambulance on the street or, or, or, or whatever. And we have this idea that, oh, we have to have this perfect, quiet, dark, comfortable... You know, they're sleeping on the ground. They don't have mattresses, right?

Dr. Rangan Chatterjee 1:59:52 Mm.

Dan Lieberman 1:59:52 So we have-- We actually make ourselves by, by cr- by having this idea of like how we're supposed to sleep, and then when it's not perfect, we then get stressed about it, which then makes our sleep worse.

Dr. Rangan Chatterjee 2:00:04 Yeah.

Dan Lieberman 2:00:04 So I think... And, and, and, and this, and what I call the sleep industrial complex. There are all these people out there and companies out there trying to make us stressed about their sleep, about our sleep, so that we buy their products or their book or whatever. Um, they're also making us stressed about our sleep. They're... And so that is the enemy of, of-

Dr. Rangan Chatterjee 2:00:20 Yeah

Dan Lieberman 2:00:20 ... of proper sleep. So the-- I always point out, I ask people, you know, "Can you sleep on an airplane?" "Oh, yeah, I fall asleep on airplanes." And, and then they tell me they have problems sleeping. It's like, if you can sleep on an airplane-

Dr. Rangan Chatterjee 2:00:30 Yeah. [laughs]

Dan Lieberman 2:00:31 ... you can, you can sleep on a horse probably. You can sleep anywhere, right?

Dr. Rangan Chatterjee 2:00:34 Yeah.

Dan Lieberman 2:00:34 So that's proof to you that you actually can fall asleep in, in, in, in all kinds of environments. It's just, it's not... It's just that you're on the airplane. You expect this noise. It's just normal. You don't expect an airplane to be quiet, you know-

Dr. Rangan Chatterjee 2:00:45 Yeah

Dan Lieberman 2:00:45 ... et cetera. So you fall asleep, right? So... Or, or for me, uh, it was when I was in college [laughs] I would go to the library, and I'd fall asleep in the library. And you know, the library's not super quiet. It's just that I was exhausted because I hadn't slept a lot the night before. You can slop- fall asleep in all kinds of environments. It's just that we make our, ourselves stressed about sleep, and stress is the enemy of sleep.

Dr. Rangan Chatterjee 2:01:08 Is myopia a mismatch-

Dan Lieberman 2:01:10 Oh, absolutely. Yeah

Dr. Rangan Chatterjee 2:01:11 ... condition?

Dan Lieberman 2:01:11 So-

Dr. Rangan Chatterjee 2:01:12 So shortsightedness, I should say. Needing, needing glasses or contact lenses.

Dan Lieberman 2:01:16 Yeah. I mean, there's a wonderful study that was done here in London many, many years ago. Done-- I think it was the first study of myopia. You know that Queen's Guard?

Dr. Rangan Chatterjee 2:01:25 Yeah.

Dan Lieberman 2:01:25 Those people with the, was it bear skin? What are they? This was kind of fur on their heads.

Dr. Rangan Chatterjee 2:01:30 [laughs]

Dan Lieberman 2:01:31 Um, uh, it was a study that was done in the ni- early 19th century, I believe, or the mid 19th century, where they showed that the, that the, that the, the common soldiers in the Queen's Guard, none of them, or very few of them, had myopia, but their officers had a high percentage of myopia. And that was the first time somebody thought, "Oh my God, there's some environmental component to myopia." And then people started studying it around the world. There's also studies where they've looked at Inuit populations in, in the Arctic, right? And they've looked at multi-generational families, and they, and the, the grandparents have perfect eyes, right? And the grandchildren now have very high rates of myopia, right? So what's going on? Well, myopia is caused by an eyeball that's the wrong length, right?

Dr. Rangan Chatterjee 2:02:17 Mm.

Dan Lieberman 2:02:17 So when your-- So if your eyeball is too long, when you refract the light, it gets... You can only refract the light so much, and so it's, it's focused. It can't get focused on the, on the cells in the back of your eye, and so your, your mi- you, you can't see, right? So you're, you have, you have... You're, you're, you're nearsighted, right? So, um, and what's causing that is, again, the eyeball is just too long. So what causes the eyeball to be too long? Well, s- I won't go into all the details of the experiments, but it turns out that people used to think it was reading, right? You know, close work, people who read too much. But it turns out it's not the reading, it's actually just being indoors in environments that don't have a lot of complex visual stimulus.

Dr. Rangan Chatterjee 2:02:59 Mm.

Dan Lieberman 2:02:59 That affects the expression of genes in the eye as the eye is developing that don't con- that control the growth of the eyeball. There's a few genes that have been identified. And, um, and so you end up growing an overly long eyeball, and you're stuck with myopia. So myopia is caused by spending too much time indoors.

Dr. Rangan Chatterjee 2:03:19 Mm.

Dan Lieberman 2:03:19 Um, and there are elegant experiments on animals where they test this.

Dr. Rangan Chatterjee 2:03:23 Yeah.

Dan Lieberman 2:03:23 And, and we can see this in, you know, populations where they've... Actually, Singapore is a, is a place where they've done a lot of really cool research on this. So, so myopia is much more common today because of, you know, we're not evolved to grow up and spend so much time indoors, which is why it's correlated with reading. Um, and hence we develop overly long eyeballs.

Dr. Rangan Chatterjee 2:03:43 Yeah. It's, it's fascinating. I've seen some research suggesting that children, we want them outside for at least two hours a day. I think there's a correlation between kids who are outside for less than two hours a day and-

Dan Lieberman 2:03:53 Exactly

Dr. Rangan Chatterjee 2:03:54 ... rates of myopia. Um-

Dan Lieberman 2:03:56 Exactly

Dr. Rangan Chatterjee 2:03:56 ... I think also one of the downsides of, um, these phones and screens and, uh, you know, homework being given on screens in the evenings. There's, there's many potential downsides. Um, one of them I think also is it encourages them to stay inside, but then also have that kind of narrow, concentric sort of vision. But you're saying it's more outdoors and actually that the act of just being focused on that near screen.

Dan Lieberman 2:04:24 That's the evidence that I've seen, yeah.

Dr. Rangan Chatterjee 2:04:26 Yeah.

Dan Lieberman 2:04:26 So it was, it was, it was, it was thought that, you know, when you focus on near screens, you're, you're, you're, you're, you're, you're pulling the, the, the little tiny ciliary muscles that are, that are pulling on-

Dr. Rangan Chatterjee 2:04:35 Yeah

Dan Lieberman 2:04:35 ... the lens create tension in the eyeball that increase pressure. But I think that's been mostly debunked from my understanding. I'm not an, I'm not an ophthalmologist, so I'm not a, you know, deep, deep, deep, deep into the literature. But when my last exploration in that literature was really more the complexity of visual-

Dr. Rangan Chatterjee 2:04:50 Yeah

Dan Lieberman 2:04:50 ... stimuli from being outside turns on genes that are important for regulation of eyeball growth.

Dr. Rangan Chatterjee 2:04:55 But I guess, you know, you're usually, uh, reading or on a screen, I would say inside anyway-

Dan Lieberman 2:05:02 Of course

Dr. Rangan Chatterjee 2:05:02 ... aren't you? So it's, that will [laughs] will be playing-

Dan Lieberman 2:05:05 Exactly

Dr. Rangan Chatterjee 2:05:05 ... into it as well.

Dr. Rangan Chatterjee 2:05:06 Hey, Daniel, it's always fun talking to you. Um, it... Th- I honestly, like, the, the book Exercised, I, it is so good-

Dan Lieberman 2:05:14 Well, thank you

Dr. Rangan Chatterjee 2:05:14 ... and thorough. It's such a fun read as well. In terms of practical advice then on the back of all the research you did. Obviously in your conclusion, you finish off the book with some, I think it's 23 sort of succinct words. Um, can I read it out?

Dan Lieberman 2:05:31 Sure, please do.

Dr. Rangan Chatterjee 2:05:31 "Make exercise necessary and fun. Do mostly cardio, but also some weights. Some is better than none. Keep it up as you age." If you were writing that book today, um, would you change any of those words?

Dan Lieberman 2:05:49 No.

Dr. Rangan Chatterjee 2:05:50 And if you were writing Exercise today, 'cause it's been out now for a few years, what would be in it that isn't currently in it?

Dan Lieberman 2:05:57 Oh, good grief. I actually haven't thought about that. Um, I don't know. I think I'd ha- do more on mental health. Um, I have a, a little bit in the book on, on mental health, but I've become more and more interested in, in the role of physical activity and how our brains function and-

Dr. Rangan Chatterjee 2:06:15 Mm-hmm

Dan Lieberman 2:06:15 ... and anxiety, depression, uh, other mood disorders. Um, um, um, I think I would... Because I, I, you know, I think if you look around the world today, we not only have a, you know, a crisis of physical health, we have a, a real serious mental health crisis. So I think what I would, I would, I really want to delve more deeply into those mechanisms and, and the data and the evidence because, uh, I think that's just as important as physical health.

Dr. Rangan Chatterjee 2:06:44 And finally, you, you grew up in the United States, and you're a professor at Harvard University, so very esteemed, very prestigious. You've also spent a lot of time with populations who maybe didn't have access to the sort of things you had growing up. And of course, we've covered a lot of the things that you've learnt throughout this conversation, and there's plenty more in your book. But I guess what I'm really, really fascinated about is having spent time with a lot of these non-industrial populations, what has being with them taught you about life and the meaning of life, and what it means to be a human on this planet?

Dan Lieberman 2:07:41 I, I think, um, the, the more time I spend with people who live lives that are very different from mine, the more I realize that, um, that what really matters is your friends and your family, and the things that, you know, what are the things that we really care about, right? Um, and, and their struggles are not that different from our struggles. It's just that in my world, I've got all this extra crap [laughs] I also have to deal with. All that is detracting my, my energy and my time from the things that I really actually care about, which is the, the people I love, the... and, and also trying to make the world a better place. And, um, and I think that's what most people try to do. Um, and we've got this crazy world now that some of us live in, and I'm very fortunate. I love the fact that I get to get on airplanes and go to interesting parts of the world and try different kinds of foods and-

Dr. Rangan Chatterjee 2:08:38 Mm

Dan Lieberman 2:08:38 ... but also what I really love is meeting people and-

Dr. Rangan Chatterjee 2:08:41 Yeah

Dan Lieberman 2:08:41 ... and seeing their lives. And I think, um, and it's really the, the commonality of the human experience, I think, that, you know, that I think that I find most moving. You know?

Dr. Rangan Chatterjee 2:08:52 Yeah.

Dan Lieberman 2:08:52 People who are... You know, I'm fortunate, right? I, I don't lack for food, right? But seeing people work so hard to get food for their families, right? Um, that's what, that's, that's what motivates them, right? And, um... Or, or trying to help their kids who are sick or, or, or, you know, uh, that's what... And that, that's what gives me, that's what makes keeps me going because, you know, and in the, in the long run, it's not about the papers I publish or, you know, how much money's in my bank account or, or you know how many, you know, people watch a video or something.

Dr. Rangan Chatterjee 2:09:26 Yeah.

Dan Lieberman 2:09:26 It's, it's really, you know, how, you know... When I die, when I die, none of that's gonna matter, right?

Dr. Rangan Chatterjee 2:09:30 Yeah.

Dan Lieberman 2:09:31 What really matters is the f- the impact that I've had on people in my life and the impact that they've had on me.

Dr. Rangan Chatterjee 2:09:38 Yeah. Peaceful answer. Daniel, you've had a huge impact on me. I think the book's wonderful. I can't wait to see what you come out with next. Thank you so much for coming on the show.

Dan Lieberman 2:09:46 Oh, it's been my pleasure. Thank you. [upbeat music]

Dr. Rangan Chatterjee 2:09:48 If you enjoyed that conversation, then I think you are really going to enjoy this one that I've picked out especially.

Guest 2:09:54 If at 37 your limit is just being able to run that 30-minute park run, at 75 you're gonna have a very difficult time getting around