Harvard Neuroscientist: "If You Sit Like THIS, Watch Out! – It Destroys Your Body" | Dan Lieberman

Dr. Rangan Chatterjee 0:00 We have been told that sitting is the new smoking over the last few years. What's your take on sitting?

Dan Lieberman 0:07 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 0:54 Mm-hmm.

Dan Lieberman 0:55 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- uh, 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 1:13 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 1:18 Oh, absolutely

Dr. Rangan Chatterjee 1:18 ... position that becomes uncomfortable after 20 minutes?

Dan Lieberman 1:21 I think it's a combination of the two.

Dr. Rangan Chatterjee 1:22 Yeah. Okay.

Dan Lieberman 1:23 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 1:46 Yeah

Dan Lieberman 1:46 ... 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 2:07 Wow.

Dan Lieberman 2:08 And, uh, so, uh, uh, Thonet, a guy in Germany, produced the first... You know, the café chair with those bentwood?

Dr. Rangan Chatterjee 2:14 Yeah.

Dan Lieberman 2:14 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 2:30 Mm

Dan Lieberman 2:30 ... 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, si- sitting for... You know, getting up every once in a while and also using chairs-

Dr. Rangan Chatterjee 2:48 Ac- more active sitting positions.

Dan Lieberman 2:50 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 2:55 Mm

Dan Lieberman 2:55 ... 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 3:04 Yeah.

Dan Lieberman 3:05 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 3:13 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 environments? 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 to const- my muscles are having to do something to keep myself upright.

Dan Lieberman 4:27 Constantly. Exactly.

Dr. Rangan Chatterjee 4:28 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 4:32 [laughs]

Dr. Rangan Chatterjee 4:32 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 5:04 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-

Dr. Rangan Chatterjee 5:22 That we've made

Dan Lieberman 5:22 ... we've made, right? So as people... We call this the, 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 and no running water-

Dr. Rangan Chatterjee 5:36 Mm-hmm

Dan Lieberman 5:36 ... 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 5:47 Yeah.

Dan Lieberman 5:47 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 5:59 Mm.

Dan Lieberman 5:59 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 6:11 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 6:20 Well, right now we're mostly studying what's going on.

Dr. Rangan Chatterjee 6:22 Okay

Dan Lieberman 6:23 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 6:33 Right

Dan Lieberman 6:33 ... in, in, in the Kenya National Museum is it, 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 6:57 Yeah

Dan Lieberman 6:57 ... yeah. This is a, this is an important message that the whole world needs to, to know.

Dr. Rangan Chatterjee 7:01 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 7:11 [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 steps meter."

Dr. Rangan Chatterjee 7:39 Hmm.

Dan Lieberman 7:40 And turns out it's actually not that bad, right? It's, uh, it's, a, you know, hun-

Dr. Rangan Chatterjee 7:45 It's not bad-

Dan Lieberman 7:46 Yeah

Dr. Rangan Chatterjee 7:46 ... as a recommendation, I think.

Dan Lieberman 7:47 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, if you have one of those watches that makes sure you get 10,000 steps-

Dr. Rangan Chatterjee 7:56 Yeah

Dan Lieberman 7:57 ... 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 8:04 Mm-hmm.

Dan Lieberman 8:04 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 my colleague I-Min Lee 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 8:35 Is there an upper limits?

Dan Lieberman 8:36 So far, I don't think she sees a limit i- for, this is for steps. It's just walking, right?

Dr. Rangan Chatterjee 8:40 So like if you could get to-

Dan Lieberman 8:41 The, the line-

Dr. Rangan Chatterjee 8:42 ... 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 8:48 That's what, that's what her data show.

Dr. Rangan Chatterjee 8:50 Okay.

Dan Lieberman 8:50 But again, there's a lot of error, variation around the mean.

Dr. Rangan Chatterjee 8:52 Sure.

Dan Lieberman 8:52 So what ha- what your benefit might not be the same as my benefit, right?

Dr. Rangan Chatterjee 8:55 Of course.

Dan Lieberman 8:56 There's a lot of variance around that mean. But if you look at the, the data on step counts in, say, all-cause mortality, hmm, it kind of evens out starting around 7,000 steps.

Dr. Rangan Chatterjee 9:07 So once you're hitting 7,000 steps a day, it's kinda like, look, you've got most of the benefits.

Dan Lieberman 9:12 Yeah. And if you did diabetes, you'd get a different curve, et cetera, et cetera. But again, there's a l- 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 9:24 Yeah.

Dan Lieberman 9:24 Or 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 9:30 Hmm.

Dan Lieberman 9:30 So we prescribe it like, you know, how many aspirin you should take or how many-

Dr. Rangan Chatterjee 9:33 Yeah

Dan Lieberman 9:33 ... 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 9:46 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 9:55 That's correct

Dr. Rangan Chatterjee 9:55 ... ish?

Dan Lieberman 9:56 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. Ra- i- instead, it's that by studying h- 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 10:42 Okay.

Dan Lieberman 10:42 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 10:50 And, and where, which country are you studying these populations in?

Dan Lieberman 10:52 We've studied them in Mexico, we've studied them in Rwanda, we've studied them in Kenya.

Dr. Rangan Chatterjee 10:56 Okay.

Dan Lieberman 10:56 Uh, that's where the f- the three main places we've done that-

Dr. Rangan Chatterjee 10:58 Okay

Dan Lieberman 10:58 ... 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 11:06 Yeah.

Dan Lieberman 11:06 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 11:19 Mm

Dan Lieberman 11:19 ... 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 11:28 Mm-hmm.

Dan Lieberman 11:28 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 i- or physical activity, I should say, right? If anything is better than nothing [laughs] right? If you're, if you're completely sedentary, just taking a few steps, you know, more steps a day, 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 12:17 Yeah

Dan Lieberman 12:17 ... uh, 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 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 12:46 Mm.

Dan Lieberman 12:46 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 13:08 Yeah

Dan Lieberman 13:08 ... all diseases if you're in-

Dr. Rangan Chatterjee 13:09 It's about reducing risk.

Dan Lieberman 13:11 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 13:20 Yeah.

Dan Lieberman 13:20 So risk is a, is a, is a statistical mess- me- measure, but it's, it doesn't really work that way for, for you and me.

Dr. Rangan Chatterjee 13:26 Yeah. 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 13:43 It's incredibly important.

Dr. Rangan Chatterjee 13:45 Yeah. So can you explain why you think it's so important based upon what you've seen?

Dan Lieberman 13:50 So one of the... You know, as people live l- longer, right? Actually, we're not living all that much longer. The data for, uh, 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 14:11 So it's not dissimilar.

Dan Lieberman 14:12 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 14:20 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 14:29 Right. And the term we use is healthspan, right? So healthspan is the number of years you live without any serious disease or disability, right?

Dr. Rangan Chatterjee 14:37 Mm.

Dan Lieberman 14:37 And so their healthspan 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 14:44 Mm.

Dan Lieberman 14:45 So we evolved to have a long healthspan, which means therefore to have a long lifespan. And, um, and one of the ways to extend your healthspan 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 15:01 Yeah.

Dan Lieberman 15:02 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 15:10 Mm.

Dan Lieberman 15:10 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 could... 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 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 15:53 Yeah.

Dan Lieberman 15:53 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 16:04 Mm.

Dan Lieberman 16:05 And that creates a condition that you know only too well called sarcopenia.

Dr. Rangan Chatterjee 16:09 Yeah.

Dan Lieberman 16:09 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 16:17 [laughs]

Dan Lieberman 16:17 'Cause it really makes you think about it, right?

Dr. Rangan Chatterjee 16:19 Yeah.

Dan Lieberman 16:19 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 16:47 Yeah

Dan Lieberman 16:47 ... consequences of physical inactivity. So healthy aging requires you to maintain your strength. It's really important.

Dr. Rangan Chatterjee 16:54 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 17:17 Well, well, we're trying to measure that now.

Dr. Rangan Chatterjee 17:18 Okay.

Dan Lieberman 17:18 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 17:37 Right.

Dan Lieberman 17:38 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. I mean, there's, 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, uh-That's helping maintain their health span

Dr. Rangan Chatterjee 18:15 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 19:00 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 19:08 Mm.

Dan Lieberman 19:08 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 19:28 Mm

Dan Lieberman 19:28 ... and those are the type, you know, they're the fast twitch. And we have the kind of intermediate muscle fiber types. And you need a good mix, right?

Dr. Rangan Chatterjee 19:33 Mm-hmm.

Dan Lieberman 19:33 You need m- mostly slow twitch for aerobic long distance endurance, for the walking, the running, et cetera. But you also need some fast twitch muscles too, right?

Dr. Rangan Chatterjee 19:42 Mm.

Dan Lieberman 19:42 And, and, um, and you also want to wire up your nervous system to your muscles kind of properly.

Dr. Rangan Chatterjee 19:49 Mm.

Dan Lieberman 19:49 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 a- 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 20:21 Is too much muscle only a problem when you can't feed it with enough calories?

Dan Lieberman 20:29 That's right, yeah. So, uh, but which is, which was n- n- normal until very, very recently.

Dr. Rangan Chatterjee 20:33 Yeah. So l- let's say you-

Dan Lieberman 20:34 So I tend to think in evolutionary terms, yeah.

Dr. Rangan Chatterjee 20:36 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 20:56 Yeah. And the good news, it's easy. You just, [laughs] just do weights a few times a week.

Dr. Rangan Chatterjee 21:00 Yeah.

Dan Lieberman 21:00 You don't have to do that much.

Dr. Rangan Chatterjee 21:01 But-

Dan Lieberman 21:02 [laughs]

Dr. Rangan Chatterjee 21:02 ... I guess-

Dan Lieberman 21:03 [laughs]

Dr. Rangan Chatterjee 21:04 ... 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 21:26 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 21:37 Yeah. So, so I kind of think g- c- 'cause I feel we can, you know, as you mentioned, you, you publish 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, 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 got to 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 22:22 Yeah

Dr. Rangan Chatterjee 22:22 ... problematic for their longevity?

Dan Lieberman 22:23 Yeah.

Dr. Rangan Chatterjee 22:23 It's a, it's a hypothetical point.

Dan Lieberman 22:25 I think it's a really interesting hypothesis. I don't know any data on it.

Dr. Rangan Chatterjee 22:27 Mm-hmm.

Dan Lieberman 22:28 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 22:36 Can you?

Dan Lieberman 22:37 Most- 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, there was actually a study done here in the UK on the bio- UK Biobank study-

Dr. Rangan Chatterjee 22:48 Right

Dan Lieberman 22:48 ... where they actually looked at, you know, a few people in the biobank who did crazy ultra stuff, right? Now, remember, these are [laughs] 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 23:25 Mm

Dan Lieberman 23:25 ... Aaron Baggish and Rob Shave and I, 'cause our cardiovascular systems evolved. There is a trade-off in, in how your heart works. So your heart's a pump, right?

Dr. Rangan Chatterjee 23:33 Mm.

Dan Lieberman 23:34 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 23:44 Mm

Dan Lieberman 23:44 ... sending through your body at any one given time. So each, each time your heart pumps, how much blood is leaving the ventricle of 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 24:04 Mm

Dan Lieberman 24:04 ... from my body, but it's now pushing that blood, uh, through a, through muscles that are contracting, lots of muscles that are contracting, and that's, and that's high pressure.

Dr. Rangan Chatterjee 24:14 Mm.

Dan Lieberman 24:14 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 24:24 Okay.

Dan Lieberman 24:24 And that's a ... And that's ... Some of that's good, right? But pe- but our cardiovascular system's evolved 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 25:00 Wow.

Dan Lieberman 25:00 So, so [gentle music]

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Dan Lieberman 26:43 People who do strength training, fine, but don't skip the cardio. You need both.

Dr. Rangan Chatterjee 26:47 And what do you mean by cardio?

Dan Lieberman 26:49 E- Cardio is any kind of physical activity that, that, that, that requires you to increase your volume, cardio ... your, your, your, your, your output. So swimming, walking, running, volleyball, game of soccer, all that.

Dr. Rangan Chatterjee 27:02 Yeah.

Dan Lieberman 27:02 And some, some sports are mixed, like s- rowing, for example. I've, I've got a ... I 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 27:14 Yeah

Dan Lieberman 27:15 ... there's some strength involved, right? Uh, that's one of the reasons why I love it. So if, if ... 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 27:24 Yeah.

Dan Lieberman 27:25 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, th- the, the endurance athletes were getting.

Dr. Rangan Chatterjee 28:03 Wow.

Dan Lieberman 28:04 And there, and there, 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 28:14 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 29:24 And evolution explains why.

Dr. Rangan Chatterjee 29:25 And evolution explains why.

Dan Lieberman 29:26 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 29:36 Yeah

Dan Lieberman 29:36 ... of evolution. And so it's the evolutionary story which explains why this is the case.

Dr. Rangan Chatterjee 29:40 Yeah.

Dan Lieberman 29:40 And I think that the evolutionary perspective also helps us think creatively about it, too.

Dr. Rangan Chatterjee 29:47 Yeah. 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 31:09 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 31:20 Yeah.

Dan Lieberman 31:20 They're looking at their watches all the time. They're looking at their splits.

Dr. Rangan Chatterjee 31:22 They're pushing it.

Dan Lieberman 31:22 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, r- 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-

Dr. Rangan Chatterjee 31:38 Yeah

Dan Lieberman 31:38 ... in the world.

Dr. Rangan Chatterjee 31:38 I know.

Dan Lieberman 31:38 It is a wonderful party. I've been to it twice. It's just amazing, right? See these people 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 31:49 Yeah.

Dan Lieberman 31:49 They're stone-faced. They're like, you know, they're just relieved. They're like, "Ah."

Dr. Rangan Chatterjee 31:52 Yeah.

Dan Lieberman 31:53 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 31:58 Yeah. It's gonna have a different impact

Dan Lieberman 31:59 ... they're, they're having a great time, and they've, they've did it. They made it. Now, now, now, does... Is the, uh, 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 32:11 Yeah, agreed.

Dan Lieberman 32:11 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 32:18 Mm-hmm.

Dan Lieberman 32:18 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 32:38 Mm

Dan Lieberman 32:38 ... 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 32:50 Yeah.

Dan Lieberman 32:50 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 33:03 Mm.

Dan Lieberman 33:03 Uh, so there, there can be... You know, everything has a trade-off-

Dr. Rangan Chatterjee 33:06 Yeah

Dan Lieberman 33:07 ... and, and, and, and extreme endurance sports are no exception.

Dr. Rangan Chatterjee 33:10 Let's talk about another mismatch disease, uh, cancer. You call this mismatch disease, and you specifically say that it's a disease of high energy.

Dan Lieberman 33:20 Hmm. This is important.

Dr. Rangan Chatterjee 33:21 What do you mean by that?

Dan Lieberman 33:22 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 set of mutations, more than one-

Dr. Rangan Chatterjee 33:41 Mm

Dan Lieberman 33:41 ... 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 33:49 Mm.

Dan Lieberman 33:49 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 34:04 Mm.

Dan Lieberman 34:04 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 34:31 Mm.

Dan Lieberman 34:31 That's basically what's going on. Hormones. There 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 have caused damage. You get more mutations. They're, they're, they're, they're, um, you know, you... I don't know if you've talked about mTOR and rapamycin on the show really.

Dr. Rangan Chatterjee 34:52 Not lately, no.

Dan Lieberman 34:52 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. People, 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. 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 35:29 Wow.

Dan Lieberman 35:29 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 35:47 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 36:05 Exactly. Exactly.

Dr. Rangan Chatterjee 36:07 Nice.

Dan Lieberman 36:07 I mean, yeah, I mean, that's, that's exactly the... You're absolutely right. So, so the mismatch is not being physically active. When we're not physically active are, are... 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 forFor, for building. Like 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 36:42 Mm

Dan Lieberman 36:42 ... 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 a- 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 conc- 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 37:09 Yeah

Dan Lieberman 37:09 ... "Oh, I've got all this extra energy. I'm gonna shunt that energy towards reproduction."

Dr. Rangan Chatterjee 37:13 Yeah.

Dan Lieberman 37:14 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 38:02 Mm.

Dan Lieberman 38:02 Right? Now, natural killer cells, I love the term, right?

Dr. Rangan Chatterjee 38:04 Yeah, me too.

Dan Lieberman 38:05 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 he- 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 38:31 Mm.

Dan Lieberman 38:31 You... Again, we evolved to do that, right?

Dr. Rangan Chatterjee 38:33 Yeah.

Dan Lieberman 38:33 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, 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 39:02 Mm.

Dan Lieberman 39:02 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 39:10 Yeah

Dan Lieberman 39:10 ... 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 is not bad for us, because our cells are producing antioxidants in abundance.

Dr. Rangan Chatterjee 39:24 Mm.

Dan Lieberman 39:25 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 39:32 Yeah.

Dan Lieberman 39:33 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 39:41 Mm.

Dan Lieberman 39:41 We're 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.

Dr. Rangan Chatterjee 39:56 Mm-hmm.

Dan Lieberman 39:56 Right? 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 40:13 What about the number of menstrual cycles a woman has?

Dan Lieberman 40:16 That's another example. That's, again, it's about energy, right?

Dr. Rangan Chatterjee 40:19 Yeah.

Dan Lieberman 40:19 Because, um, menstrual cycles, um, typical in a natural fertility population, w- which, by which I mean people aren't using, um, 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 40:47 Yeah, they're not having periods.

Dan Lieberman 40:48 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 of about 400-

Dr. Rangan Chatterjee 41:10 Yeah

Dan Lieberman 41:11 ... 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-

Dr. Rangan Chatterjee 41:26 Yeah

Dan Lieberman 41:26 ... including breast cancer.

Dr. Rangan Chatterjee 41:27 I, 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 41:35 Yeah.

Dr. Rangan Chatterjee 41:35 You know, 'cause it's fascinating that, you know, 150 versus 400, let's say on average, that is a huge difference.

Dan Lieberman 41:43 Yeah.

Dr. Rangan Chatterjee 41:44 You know, over the course of a life.

Dan Lieberman 41:45 Yeah, absolutely. Or, or, you know, uh, insulin levels. The people walking around today that we see in the streets of London, the estimates we have or the, the data we have, there's everybody's walking around with higher levels of insulin-

Dr. Rangan Chatterjee 41:59 Mm

Dan Lieberman 41:59 ... 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 42:05 Yeah.

Dan Lieberman 42:05 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 42:22 What, what did you see, uh, in relation to fasting in some of these hunter-gatherer or more traditional populations?

Dan Lieberman 42:28 Well, they just don't eat all the time. I mean, look, in my building, right, you know, um, there's a snack machineThere's, uh, right at the bottom of the stairs, right?

Dr. Rangan Chatterjee 42:36 This is in Boston?

Dan Lieberman 42:37 Yeah, uh, in my, my building at Harvard, right?

Dr. Rangan Chatterjee 42:39 Yeah.

Dan Lieberman 42:39 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 42:54 Mm

Dan Lieberman 42:54 ... 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're just not surrounded by food, and you're not surrounded by high energy food.

Dr. Rangan Chatterjee 43:29 So to me, 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 43:42 They, they have no choice, right? You know what I mean?

Dr. Rangan Chatterjee 43:43 Yeah.

Dan Lieberman 43:43 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 43:51 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 44:13 I'm gonna 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 44:20 Where was this?

Dan Lieberman 44:21 This is in, in Tanzania. And, um, and we had ... You know, we came with a few Jeeps and 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 45:02 [laughs]

Dan Lieberman 45:02 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 you, you and I might like, "Okay."

Dr. Rangan Chatterjee 45:15 Yeah.

Dan Lieberman 45:15 "I don't need to eat thirds," right? But they, they, they were, they were s- they, they were happy. And then we, 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 45:31 Yeah.

Dan Lieberman 45:31 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 45:47 Yeah.

Dan Lieberman 45:47 They have to go out and find it.

Dr. Rangan Chatterjee 45:49 Everybody listening and watching to this right now, Daniel, I'm sure is aware that physical activity is going to be beneficial in some way for them. And as a society, we're trying to move more. Uh, you know, I'm a medical doctor. You know, we're always being told that we should be encouraging our patients to move more and actually to exercise, which potentially is problematic. But it, it's interesting, isn't it, that we're moving less as humans, but we're living longer.

Dan Lieberman 46:22 Yeah.

Dr. Rangan Chatterjee 46:22 So what's going on there?

Dan Lieberman 46:23 Well, I mean, I think it's part of the, the confusion people have, right? We're told that, you know, exercise is medicine and that if you don't exercise you'll get sick. And then they look at people like ... Well, I'll, I'll be very political. They, they look at people like Donald Trump, who, who doesn't exercise, um, and actually believes that exercise is, like, wastes your energy, right? And, um, and they see he's, you know, President of the United States in his 70s, and they wonder what's going on. And, and the answer is that, uh, you know, I think we oversimplify, um, something that is, uh, very important, which is that exercise really does improve your health. Exercise really decreases your chances of getting sick. Um, but on top of that, we have an incredible medical system, as you well know. You're a practicing physician. Um, and we're able to patch people up and keep them going and, and, um, and, you know, treat their diseases and, you know, give them pills to lower their blood pressure and other pills to lower their cholesterol and all the other sequela, the things that result from being physically inactive. And we can keep going. Um, but, but it comes at a cost. And it comes at an increased risk and an increased vulnerability of a wide range of diseases. Just, just, you know, the data are unquestionable. 150 minutes a week of physical activity, just, you know, a brisk walk, uh, can lower your relative risk of dying at a given age by 50%. Um, that's not a, a number I just pulled out of a hat. That's a really, really, really solid number based on, on many, many, many studies. Um, but it, it's not a, it's not a magic bullet. It's not a, you know, guarantee of good health. You could still get cancer. You could still get injured. Um, and, um, and vice versa. So we, we, we need to, you know, be kinda clear about what the benefits are, but also the fact that it's, this is a statistical issue, and it's a complicated issue, and there are no simple solutions to anything.

Dr. Rangan Chatterjee 48:10 So why is it when the data and the science is really clear that, as you say, 150 minutes of physical activity each week will have multiple benefits ... Or, or let me rephrase that. Uh, may have multiple benefits on your wellbeing and your longevity. Why do so many of us struggle to do that?

Dan Lieberman 48:30 Because it's, it's, it's abnormal. I mean, it's ... Our instincts-

48:34 ... are constantly pulling us not to exercise. I mean, our, our instincts are deep and they're powerful. I mean, for, for millions of years, our ancestors struggled to get enough energy to eat, right? They, every day they had to work. They didn't go crazy hard. You know, they didn't, like, work eight hours a day on their feet, you know, you know, struggling to get enough food. They, they ... You know, average hunter-gatherers seemed to work, you know, moderately hard for about two and a half hours a day, two and a quarter hours a day of, of ... You know, and then light, light tasks for the rest of the day. And they, they sit as much as we do, around nine to 10 hours a day. But, but that, that gave them just enough food to survive. Um, you know, there, there are no obese hunter-gatherers, right? And, and if they were to go for, like what I did this morning, go for a, a long run just for the hell of it in the morning, um, they would then waste all that energy, which they could use towards reproduction and the things that natural selection cares about. So nobody in the Stone Age ever went for, for a morning run for the, for the fun of it. And it's, it's a bad idea. And s- and, and, and, and, and whenever you have a chance to save energy, you, you, you should, uh, u- u- until recently. And now we live in this really strange, interesting, modern world, wonderful in all kinds of one- in regards, where we can, you know, spend our entire day without ever getting our heart rate up, you know, press buttons to get food, and shopping carts, and, and, and ... You know, I don't even have to move my hand when I brush my teeth if I didn't want to. You know, I get an electric toothbrush, right? I mean, everything is mechan- mechan- mechanical and, and, and the result is that we no longer have to be physically active, and we now have to do something really weird, which is to, which is to choose to be physically active.

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Dan Lieberman 51:22 Uh, and, and although we know up here, right, in our brains that it's good for us, all kinds of instincts just kick in to tell us not to. I think the best evidence for that are when you have, like, a stairway next to an escalator, right? You must see them-

Dr. Rangan Chatterjee 51:35 Yeah

Dan Lieberman 51:35 ... you know, there are in tube stops all over the place, and then, you know, s- uh, uh, in airports, everywhere. We all, we all know this phenomenon, right? And, and it doesn't matter where you are in the world. People have studied this in Japan, and in Denmark, and in America, and in Israel and, you know, various places. Wherever there is a stairway next to an escalator, less than 5% of people take the stairway.

Dr. Rangan Chatterjee 51:57 Wow.

Dan Lieberman 51:57 And if you put a sign up, that just goes up just a wee bit, right? If you put es- escalators in the Kalahari Desert, you know, they would take the escalator there, too. It's an instinct.

Dr. Rangan Chatterjee 52:06 Yeah. And I, and I think what you just said there about the Kalahari Desert really [clicks tongue] ... I think it brings it to life for people. Because a lot of people feel bad. They feel guilt. They, they feel shame that they're not moving as much as either their doctor has told them, the, the news has asked them to do, or even people they're following on social media-

Dan Lieberman 52:28 [laughs]

Dr. Rangan Chatterjee 52:28 ... who, you know, post a photo, "Hey, just did my, uh, 10K, uh, run before breakfast. How are you all doing today?" You know, that kind of meme, which I think if you, if you find it inspiring and you're like, "Oh, well, man, I didn't do anything. I wanna do that," great. But for many people, they watch that and they're ... And day in, day out, they're feeding their brains with that, thinking, "I'm some kind of failure. Like, look at all these people who can move their body every day and are vibrant and are full of energy, yet just getting through the day is a real struggle." And I think that's one of the beautiful things in your book, is that you, you help people not to feel bad about it. You're sort of arguing that we've not evolved to exercise.

Dan Lieberman 53:11 Absolutely. We didn't. We're ... Look, we also didn't evolve to go to school, right? I mean, uh, we didn't ... You know, u- until recently, almost nobody read, and nobody ... Nobo- of course, schools didn't exist, right?

Dr. Rangan Chatterjee 53:21 Mm.

Dan Lieberman 53:21 I mean, there are so many things of our modern world that are good for us. I mean, no, no parent thinks that sending their kid to school is bad and they shouldn't, you know, learn, that their kids shouldn't learn to read. But, but, you know, that's also a modern abnormal thing. And, and think about how we get school to work, right? We make it compulsory [laughs] . But we also try to make it fun, too, right? You know, we have recess and all kinds of ... You know, you meet your friends there. And we try to make school both fun and necessary, and I think we should treat educ- e- exercise the way we treat education. It, because it's, it's a modern abnormal thing, but it's good for us. And, and, and we should, we should make it necessary, but we should also try to make it fun. But the last thing we should do is make people feel bad about it, because [clears throat] making people feel bad about, about doing what's natural for them, um, doesn't help anybody. And I think the same thing goes with dieting, right?

Dr. Rangan Chatterjee 54:12 Yeah.

Dan Lieberman 54:12 I mean, we never evolved to lose weight. Um, but we all ... A lot of people are trying to lose weight, and for good reason, but, but when they fail on their diet, it's not because of some moral failing. It's because there are hundreds of adaptations in their bodies which wanna hold onto that fat, um, and, you know, and, and, and, and elicit a, a kind of a [clears throat] A fast, you know, a, an energetic crisis in their bodies to hold onto that energy, and it's not their fault that they're having a hard time-

Dr. Rangan Chatterjee 54:39 Yeah

Dan Lieberman 54:39 ... losing weight. It's, it's the fault of their, their biology, and yet we, we then blame them and make them feel bad. And I think we need to understand that our bodies aren't... We don't just get to decide what we do with our bodies. Our bodies are evolved and, uh, over millions and millions of generations, and we ha- and we need to be compassionate and understand that and work with our biology to find better solutions. I mean-

Dr. Rangan Chatterjee 55:00 Yeah

Dan Lieberman 55:00 ... what we've done with exercise is we've medicalized it. But, and I've nothing wrong with the medical profession. Obviously, I, I almost became a, a physician myself, but most doctors' job is to treat people when they're sick, not to prevent them from getting sick, and that's part of the medical system as a whole. That's another issue. But, but the other thing we've done with, with, with, with exercise is we've commercialized it. We've industrialized it. We've commodified it. Uh, you know, tell people to just do it, right? And, and again, there's nothing wrong with medicalizing exercise. There's nothing wrong with commercializing and industrializing exercise. But clearly it's not enough because, like in the United States... I don't know what the data are in England. I've been trying to find good data in England. There's not as much. But, but in the United States, only 20% of Americans actually exercise in their leisure time. That's a really staggering number, right? Um, you know, there are people who are physically active, you know, um, but, but, but not many people actually get out and do it, and there's a reason for that. It's not because they're lazy or, or bad or, or, or, or should feel guilty or ashamed. They're just being normal human beings.

Dr. Rangan Chatterjee 56:01 Yeah. You know, it, it, it really is wonderful to have someone with your pedigree. You're such an esteemed, highly respected researcher, professor. You're basically saying we need to be kind to ourselves. We need to be compassionate to ourselves. You're making the case with, you know, for physical activity and exercise that we need to be compassionate to ourselves. But I love what you said there about trying to lose weight. We've not evolved to lose weight. And what you just said, what, what you just mentioned there is a sort of central case I've been writing about over the last few months for my next book, which is on weight loss, and I, I very much agree. We have to be kind and compassionate to ourselves and understand we're kind of fighting our biology. You know, the, the environment in which we live is very much re- so removed from the environment in which we've evolved that therefore, you know, we're not doing anything necessarily wrong. We're just doing what humans have always done. Humans have always tried to make things easy, right? We've always looked for high-calorie, energy-dense foods to, so, you know, for as little energy as possible. It just so happens now that on my smartphone I can go on a shopping app and have that delivered to my house without actually moving anywhere. So i- I think it really does help people feel better. I, I read an article with you, Daniel, recently that I think you wrote in the British press, and you said in it that you were the kid who never got picked for the sports team at school. Yet here we are, we're having a conversation, and it's early your time. What is it? 7:30? Quarter to 8:00, something like that?

Dan Lieberman 57:35 Uh, no, 8:30. It's not that early here.

Dr. Rangan Chatterjee 57:37 8:30.

Dan Lieberman 57:37 Yeah.

Dr. Rangan Chatterjee 57:37 But you've already been for a run. And that made me think about what you've just said about we've gotta make it fun for people. Uh, we've gotta... You know, you, we made school compulsory, but we also try and make it fun, and you're sort of making a similar case for exercise. So is part of the problem also, like with you, and o- o- you've obviously overcome that and you are still, uh, someone who moves regularly, but many people have that experience at school. They're not picked for the teams. They're made to feel, uh, shame and bad about themselves, that they can't be sporty like their friends who have been picked in the team, and that puts them off moving their bodies for life.

Dan Lieberman 58:17 Oh, absolutely. I mean, I, I, I, I was lucky because although I was terrible in s- I really was picked last for sports. [laughs] I, I, I, for example, played on a, on a soccer team. I g- you call it football. Um, and, uh, in, in my town that I grew up in, I was a, was a really good, good, good soccer town. And so there were kids on my team who were w- so much better than me. I just sat on the bench. You know, I almost never got to play because I wasn't very good. And, um, you know, I, I j- I, I felt very insecure about my body and, and, uh... But I was lucky that I had parents who loved to hike and loved to s- we went skiing in the winter, cross-country skiing, and, and my, my mother, you know, jogged, and my father jogged, too. And so they were physically active, but they didn't play sports. I don't think they ever watched any sports event ever, I don't think. Um, [laughs] I played tennis a bit, but, you know, that was, um... You know, I had to walk to a tennis court. That was fine, but, you know, they, they weren't interested in any of that. I don't think they ever came to any game I was ever in, partly because I sat on the bench, right? But, um, um, uh, so I kinda grew up thinking that it was sort of normal to be physically active but not interested in sports. But so much of physical activity that kids encounter is sports. And sports, you know, there's a whole chapter in my book on sports. Sports can have exercise, but it [laughs] doesn't always have exercise, and that exercise isn't always necessarily healthy. Look at American football. I mean, that's a really profoundly unhealthy sport. Um, um, and we have more and more data, uh, to show that, not just, not just in terms of concussions but also in terms of heart disease and other kinds of problems that, that arise from, from, you know, bulking up, making these sort of sumo wrestler size sort of linemen in the, in the s- in the f- in the sport. But, but we, you know, we, we, we, we could do a better job of making it fun. I mean, some schools do that. Um, but, um, and making sure it's about fitness. I m- m- my university, Harvard, has, um, you know, an, a, a huge athletics program. We have 40 teams. Um, one of the largest athletic programs in the United States, even though this is not a powerhouse school in terms of athletics. But, um, um, but the, the, the athletics department really mostly serves the athletes on campus, and their j- job isn't really that much to get the other 80% of students, um, to be, to be physically active. And, and, and sh- surprise, surprise, the vast majority of Harvard students, about 75%, don't meet the minimum level of physical activity, um, uh, that you would need in the United States.Um, and, and that's partly because we don't make it fun for them. You know, there's no opportunities for them. And probably most of, and all of them would like to do more exercise, but they, they're busy, and they're stressed, and they've got courses and classes, and they don't have to do it. And, and, you know, we could do a much better job of helping them, uh, be active, and they want us to do a better job of helping them be active. It's not something you can just snap your fingers and do on your own.

Dr. Rangan Chatterjee 1:01:06 It's an interesting dilemma, isn't it? That we, we s- we, we, we, we look up to these incredible athletes, uh, with superhuman performances, you know, the American footballers, let's say, in the States, or, uh, you know, Eliud Kipchoge, the runner who can, you know, run a marathon, frankly, in a time that l- just makes me shudder even thinking about the fact that he can do [laughs] that in under two hours. But there's a difference, isn't it? It's what you're, it's the case you're sort of making, that that's kind of elite

Dr. Rangan Chatterjee 1:01:36 performance. It doesn't mean that's healthy. It doesn't mean that's what we should all be striving for. And, and I, I think why I find that interesting is because... Have you heard of Parkrun? You familiar with Parkrun?

Dan Lieberman 1:01:49 Yes, of course. Yeah. No, it's wonderful, Parkrun. Fantastic.

Dr. Rangan Chatterjee 1:01:52 Yeah, but I, I mean, I'd love to talk about Parkrun at, at some point because there are so many aspects there, community, um, you know, uh, the social aspect to moving together, whether it's run-walk, whether it's walk, whether it's running. Um, but you also get timed at a Parkrun. And I've often wondered, is timing it a good idea or not? Because loads of people who suffer with mental health problems, Parkrun is actually what really, really helps them. That, that strong sense of community. You're moving. You're, even if you're a volunteer at that Parkrun, you still get a lot of benefits. But I wonder then when the timing comes in, and I'm not against it, I'm just sort of posing the question, does that start to make us think about performance and taking us away from just doing it because it's a fun thing to do for some of us?

Dan Lieberman 1:02:46 Well, I th- yeah. I mean, I think, I think, I think we, you know, there's so many different motivations that people have, and I think we need to, we need to, um, embrace them all, right?

Dr. Rangan Chatterjee 1:02:55 Yeah.

Dan Lieberman 1:02:55 For some people, timing is great. It gives them a little impetus. It gets them, gets them, gives them, you know, d- you know, it helps them, you know, do a little better and, you know-

Dr. Rangan Chatterjee 1:03:04 Yeah

Dan Lieberman 1:03:04 ... challenge themselves. Other people find it defeating and then, and, and, and, and, and off-putting. And, and so I think, you know, we should let a thousand kinds of physical activity bloom, right? And if, and if, and if, you know, Pa- you know, there's never gonna be one type, right?

Dr. Rangan Chatterjee 1:03:18 Yeah.

Dan Lieberman 1:03:18 For some people, why not just dancing? I mean, I, well, I have a section in the book on dancing, which is-

Dr. Rangan Chatterjee 1:03:23 You do, and I've got that written down to talk to you about 'cause-

Dan Lieberman 1:03:25 Yeah

Dr. Rangan Chatterjee 1:03:25 ... I didn't know that at all. So please-

Dan Lieberman 1:03:27 Yeah

Dr. Rangan Chatterjee 1:03:27 ... do expand on that.

Dan Lieberman 1:03:28 Yeah.

Dr. Rangan Chatterjee 1:03:28 It was a brilliant section.

Dan Lieberman 1:03:30 Yeah, I mean, every culture in the world, I, I can't find an exam- an exception, has, has not only just dancing but endurance dancing as part of its, as part of its culture, you know? People, people dance for hours, um, in, just, just about every culture. And I even, y- even in Jane Austen, I found some wonderful quotes in Jane Austen in, you know, Georgian England where people, you know, dance the night away, right? Um, um, it's, it's, it's a way of making physical activity... And they probably didn't think of it as exercise. It was social. It was fun. So there are many, many ways for us to get our bodies moving and to, and, and to, and get the benefits, the, the mental health benefits, the physical health benefits. And I think we should, if we're gonna be successful, we need to try to, you know, we n- there's not, not gonna be a one-size-fits-all approach, right? There's gonna have to be many approaches. I mean, look, there are some people, I, yeah, as you, as you know 'cause you read the book, throughout the book I make fun of treadmills because treadmills are, you know, for me, the apotheosis of exercise. Here's a machine. You know, you have to spend money to buy it or spend money to go to the gym to use it. It makes you work hard to basically stay in the same place. You get nothing done. It's loud. It's noisy. You know, it's, the air is fed in. I mean, I, you know, I, I put people on treadmills for a living, but I hate treadmills. I mean, I have one in my basement, and I sometimes use it. So what some people do is they, they, you know, they listen to a podcast or maybe, maybe this podcast or, or they'll watch a movie or, or, or whatever to tolerate the treadmill. And, you know, if that, if that works for them, that's great. There's nothing wrong with that if... It's actually very efficient. You can do two things at once. You can listen to a podcast and get some fit- exercise at the same time. But, but others just can't stand it. So let's, let's not be judgmental. Let's, any, any way that works is, is great. I mean, and we just have to support them all.

Dr. Rangan Chatterjee 1:05:12 I'm a big fan of individualized and personalized approaches, and I really like that idea that maybe we've gotta broaden out what we recommend s- to people. Say, you know, it doesn't matter, um, how you move your body, but you just wanna move it more, um, and find what actually works for you. But are there any sort of universal principles when it comes to movement that actually do work for all of us?

Dan Lieberman 1:05:40 In terms of getting us to move? I mean, I, again, I go back to the simple... I mean, my, my, you know, I think there's two, again, two basic impetuses that have, you know, over, over millennia have been the basis for w- how and why people move. And one is it, because it's necessary, and the other is because it's fun. And for most people, fun involves social. Um, um, so, uh, sometimes, you know, sometimes going for a run by yourself or a walk by yourself is meditative, and it's nice to be by yourself, and you can think through a problem. But for most of us, you know, we like to be with other people, and so s- that's why Parkrun is so successful. It's social. Here in Cambridge, we have the November Project. Every Wednesday people do these wonderful runs, and they run up the stadium, and they do all kinds of great stuff.

Dr. Rangan Chatterjee 1:06:25 Wow.

Dan Lieberman 1:06:26 We have, you know, all around the world there are various kinds of, of, of social events. There are... You know, dancing is social. Um, uh, playing a game of, you know, soccer or football is social. I mean, the list goes on, right? Um, and, um, and there are many ways to do it socially, and I think, so, so that's critical. Um, but, but that's never gonna be enough for some folks. And, and, and, you know, exercise, physical activity used to be necessary in our lives, and that was the impetus that people had to get out and, uh, you know, every day and, and do work. And so we need to find ways, without coercing them-... un- un- unethically, uh, to make exercise, to make physical activity necessary. And, and because it's not appropriate to tell adults that they, you can't, they can't have the benefits of society unless they exercise, right? Um, we, we need to help people help, help themselves, and I think the way to do that is through what's called a commitment contract. So let me go again back to education. In education, we ha- education works on a commitment contract basis for adults, right? So I'm a professor in a university where people pay ghastly sums to go to Harvard, right? I mean, I think the tuition is, and, and, and room and board and all that costs like 60 to $70,000 a year. That's full, full. Of course, most students don't end up paying that. I mean, the vast majority get financial aid. So, so [laughs] don't worry, most of my students are not fabulously wealthy. Actually, many of them are first-generation students, 'cause we have... We're lucky, we have really good financial aid. But anyway, somebody's paying 60 to $70,000 every year for them to go to school, and there's some commitment from them to go to school. And, and w- and what are they doing? They're having people like me torture them, right? I make them take exams, I make them read books, I make them stay up late at night studying, and if they don't do well, I give them a bad grade, which, you know, which, you know, stigmatizes them for the rest of their life. And, and, and, um, but they do it willingly because, because they've signed a kind of a commitment contract, whereas, whereas they're paying money for me to make them do stuff which they know is good for them, which they wouldn't, otherwise wouldn't do for themselves. And we do all kinds of other commitment contracts in our, in our, in our world, and, and I think exercise is, should be part of that. We should, we should find exercise... You know, there are many w- so there's a wonderful program called stickk.com. It's a website run through, uh, some economists. They used to be at Yale. I'm not sure if they're still at Yale. Where you can basically pick either a stick, carrot or a stick, right? And, and I describe this in the book 'cause it-

Dr. Rangan Chatterjee 1:08:50 Yeah, you do, yeah

Dan Lieberman 1:08:50 ... a funny article about this. 'Cause there's a friend of mine in, in San Francisco who was, who has been trying to lose weight, and she, uh, gave stickk.com, I think, $2,000. So not an un- not a small amount of money. And every week she agreed that she was gonna walk a certain number of miles, and if she didn't get those number- miles in, and her husband was her referee, if she didn't do those miles as affirmed by her husband, they would automatically send $50 that week to the National Rifle Association.

Dr. Rangan Chatterjee 1:09:19 [laughs]

Dan Lieberman 1:09:19 That's the big association that tries to prevent, uh, gun control laws in the United States. And she is very, very much hates the NRA and wants to see gun, gun... And she has never missed a week of her walking since she's been doing that. So she, she signed a commitment contract, put some money behind it. Now, that's a kind of an extreme one, but there are other ways we can do it, just with, through a friend. I mean, a lot of the, my early morning runs, I don't... You know, at 6:00 AM, I do not wanna run, I promise you. I mean, nobody-- I wanna be in bed with my wife, right? But I often meet a friend of mine, uh, who's a cardiologist, and he's up at 6:00 AM, and he doesn't wanna be there either. But we kind of agreed the day before that we were gonna meet each other at 6:00 AM, uh, to go for a run, and, uh, usually we're just, like, irritated at each other, and we don't even speak for the first, you know, 10 minutes. Um, and then slowly we warm up, and I'm never unhappy that I did that run at the end, but I, I, I did it because I f- I coerced myself through a commitment contract.

Dr. Rangan Chatterjee 1:10:14 Yeah. V- v- very, very practical and pragmatic approach. I guess what you're saying is that the way we've typically encouraged physical activity has been, you know, very prescriptive. You have to do this. Um, you know, if you don't do it, you're not really looking after yourself. You sort of have to rely... We, we, we're very much putting it down to individual motivation, individual willpower, and what you're saying, I, I guess, is that this is not working, right? We've not evolved to exercise. We, we're, we're now living in a society where we simply don't have to anymore. That necessity has gone. So you need to find a way to make it necessary, and the way you've found of doing it is you're meeting someone. So if your buddy has gone to the trouble of getting up early in the morning and goes to your agreed spot, and you don't show up, there is a bit of... You know, you have social pressure to show up, which is why so many movement programs talk about, you know, doing it with other people, right? Because if you're leaving it up to yourself to motivate yourself, there's gonna be times... Like, I know when I got into Parkrun, I remember thinking, at the time I wasn't really a runner, right? And we can, we can, uh... Let, let, let me put it another way. I didn't perceive myself as a runner, whereas now I do. But I still went because I did it with my son, uh, is, is reason one, and reason two is there was this big community there, this really friendly community at Parkrun. So I just had to make sure that my son and I were at the start line by 5 to 9 on a Saturday morning, and if that was... If, if I got there, I would complete a 5K. But if I had to do that myself, even if I had to do that s- myself with my son, I bet you some Saturdays we wouldn't do it. And so I think that accountability piece is, is... I think it's really interesting. Now, y- you mentioned you're

Dr. Rangan Chatterjee 1:12:15 not a fan of coercion, yet you write, uh, a very surprising, certainly surprising to me, you write about, is it the Swedish, uh, is it Björn Borg?

Dan Lieberman 1:12:26 [laughs]

Dr. Rangan Chatterjee 1:12:27 The, the Swedish underwear, sportswear manufacturer.

Dan Lieberman 1:12:30 Yeah.

Dr. Rangan Chatterjee 1:12:30 And I was mesmerized reading that story. So I wondered if you could tell that, and because that's actually taking a quite different approach, right?

Dan Lieberman 1:12:37 Yeah. I had so much fun doing that. So I, I was in, I was thinking about this, you know, 'cause I... The last section of the book, the last quarter of the book is really about how to apply the sort of natural history of exercise to the modern world, and I was interested in this idea of coercion, and I wanted to see if I could find an example of people who are forced to exercise, adults. I mean, we force kids to exercise in school, but nobody, nobody blinks an eye at that 'cause we force kids to do all kinds of stuff and think it's totally acceptable, 'cause children can't make up their own-You know, children aren't responsible for their own decisions, but adults are. And I, so I was, I was searching throughout the world. I was looking, I was thinking about, like, monks in Asia who are forced to do things and whatever, and I was... I wanted to... You know, I'm very into participant observation. I like to try what I study. And so, you know, that's why I've tried barefoot running and the... I've, you know, I try to, I try to... That's why I've chased animals on, you know, done, done races against horses and, you know, I'm, I'm into that. I like, I like

Dr. Rangan Chatterjee 1:13:27 W- we're, we're gonna come to all that, believe you me. [laughs]

Dan Lieberman 1:13:29 Yeah. I like to put myself in the shoes of the, or the, uh, of the, of the, of the, the people I'm studying. And, um, and so I, I found on the web a few articles about the Björn Borg company. It's a company in Sweden that makes, uh, mostly underwear, but other kinds of sports clothing. Um, it's no long- actually no longer owned by Björn Borg, but it's, um, uh... And, and, you know, it's... You know how those p- companies have those, like, little contact me thing? So I, you know, late at night, I, I remember telling my wife I'd found this company and I'd read some articles, and she, she said, "Well, contact them." So I, I, I, I got on the contact page and I said, you know, "Dear Björn Borg company, I'm a, I'm a professor at, you know, whatever. I'm interested in this topic and I'm kind of curious to learn more." And I remember going to bed and saying to her, "Yeah, I'm sure I'll never hear from them." And then the next morning in my in- inbox was an email saying, "Come and, come and join sports hour. [laughs] Come any time you want. We'll, we'd be happy to show you." [laughs] So I, uh, so I was on sabbatical and I had some time, so I got on an airplane and I went to, to, you know... Uh, they were very kind and they told me when to show up. So I, I, um, I showed up and they basically said I could talk to anybody in the company and, you know, I had to go to sports hour 'cause at Björn Borg company, everybody has to exercise. It's, it's, it, there's, it's a requirement. And e- there's a sports hour o- every Friday at, I think it's 10:00 AM. And, and there's no excuses, unless, unless you're injured or whatever, uh, or something like that. If you're a board member, if you're a visitor, it doesn't matter who you are. If you sweep the floors, if you're the CEO, doesn't matter. You go to sports hour. And so I, I went to sports hour, which is a really hard kind of CrossFit workout. Uh, it was great. It was exhilarating. And you, you can do it as hard as you want or as light as you want. Um, and, um, and then they have all kinds of other events where they, you know, instead of a Christmas party where everybody gets drunk, they run through the streets of Stockholm and have hot chocolate afterwards, you know? I mean, it's a, it's a delightful environment. But of course, you know, not everybody liked it and some people left the company, but some people who are in the company love it. And I just talked to folks about it and see, to see how it worked, and to my surprise, it was a, it was actually pretty popular. Um, and, um, uh, the people actually kind of realized that it was a beneficial thing. But I should also say these are people who've drunk the Kool-Aid, as we say in the United States, right? The, you know, everybody who really hated it has obviously left the company, you know? You wouldn't b- be in that company if you didn't think this was acceptable. But, um, but you know, the fact of the matter is that's, as far as I can tell, the only company in the world that does that, and we're not gonna find... You know, that's just not gonna work in most places, and we have to find other ways, uh, to make exercise necessary.

Dr. Rangan Chatterjee 1:16:05 Yeah, what, what's interesting about that company for me, uh, and, you know, y- you're absolutely right. There is, there's that inbuilt bias, isn't there? Because people, I guess some people, if they know that about the company and that's not their kind of thing, they may not even apply for a job in the first place. If they start working there and they think this is a good idea, but then they feel it's too much pressure, there's, you know, there, there's some sort of camar- camaraderie that they don't like or they don't thrive on, they might leave. Um, but it's an interesting model, and I appreciate this cannot be rolled out across society. There's a kind of ethical point there, I think, as well. But you know, I, I wonder what you think about the ethics of that, where a company says, "Hey, look, we..." A- and again, I'm, I'm not speaking for that company 'cause I don't know the, the ideology behind it, but let's say a company felt that, well, we know physical activity is imp- is important because it will help the employees, it will help them with their health and wellbeing. It's gonna help them concentrate, focus, be more productive. It's a great way of bonding. Um, you know, w- I, I guess what, what would happen if companies started to... Some companies were like, "Well, look, this is part of the culture here, and if you wanna work here, this is sort of what we would be supporting." It's, it's quite a tricky one ethically, isn't it? Because it could be done in a way where it's very supportive and it's like, well, if you just wanna walk for that hour round the gym, that's fine. You know, there's gonna be no pressure on you from your manager or from the boss. You know, I know, I know it, it... You'd, you'd have to demonstrate that there was no discrimination by doing that. But it, it's working there. I mean, could that be a, could that be a s- you know, you're saying that we need to take personalized approaches.

Dan Lieberman 1:17:56 Well-

Dr. Rangan Chatterjee 1:17:56 So could that work for some companies?

Dan Lieberman 1:17:58 Well, I mean, let's, um, let's, uh, let's rev- let's flip the question and ask did that used to work for some companies? So, so in the United States, um, as in e- every, every, you know, in, in Europe, um, universities are kind of like companies, and every university until recently required students to exercise. Uh, in the United States, physical activity, physical education was 100%, you know, every single university in the country, Harvard included, required physical education.

Dr. Rangan Chatterjee 1:18:23 Wow.

Dan Lieberman 1:18:23 Um, and, and, you know, going back to, to the ancient, you know, Greek philosophers and in, you know, the traditions in India and China, everywhere in the world where you had educational systems, which of course were for elite people, right? 'Cause, uh, peasants didn't go to, go to school, but, but n- but wealthy aristocrats did. With no exception, educa- uh, exercise became part of people's education because people n- understood that there was a relationship between exercise and, you know, phys- the body and the mind, right? Mental health and physical health, and that exercise is good for students. And, um, that was dropped in the United States in, starting in basically in the '70s. So Harvard, for example, got rid of its physical education requirement in the 1970s. Um, and now, you know, we kn- we see the, we see the results. But these are adults, you know? These are 18-plus-year-old people, and it was required. And, um-Um, so, you know, I think this... And, of course, until recently everybody had to be physically active to get to work. They had to, you know, walk to get to work. They, they didn't have elevators to get them to their floor. You know, I mean, we could go on with all the things that have changed in the world. So we've kind of shifted our, our, our, our workplace and shifted our, our schools without shifting, uh, the, the, the, the kind of how we approach our bodies. And so maybe Björn Borg Company is going back to something very ancient in a new way. Um, but, um, but, you know, we, the fact that we're so uncomfortable with it, I think is interesting. Um, we're, we're, we're just so worried about, about, about, about coercion and people's rights and, and for good reason. Um, but we're also, um... I think, I think sometimes w- we, you know, we also... I'm gonna probably get myself in trouble now. Um, but look, I think it's... As you can probably tell, I'm very opposed to body shaming and fitness shaming, right?

Dr. Rangan Chatterjee 1:20:13 Yeah.

Dan Lieberman 1:20:13 It's, it's, it's unacceptable. Um, but sometimes I think because we're so worried about body shaming and fitness shaming, we, we go, we go s- to the extreme and basically turn off the whole system.

Dr. Rangan Chatterjee 1:20:26 Yeah.

Dan Lieberman 1:20:27 And, and I wonder if the, if, if we can't have our cake and eat it too, so to speak, right? Can we find a way to help people be physically active without engaging in body shaming, without engaging in fitness shaming? And I think we can. And again, I'm gonna go back to my commitment contract model because if... Let's just say you're, you're unfit, you're overweight, you're struggling, you hate to exercise, but you wanna, you wanna get... You wanna exercise. Now, if I told you I had... You had to go to a CrossFit, you know, workout every week and, you know, do 150 burpees with a, with this, you know, highly muscled, you know, you know, nutcase in front of you who's your boss, you'd, you'd hate it, right? But if you could just walk 20 minutes a day, climb the stairs, right? Pick your own goal and work towards that, you know, that would fit your, your fitness level, your, your, your, your... You know, you could do it, uh, on your own, you could do it with friends, et cetera. Not in a way that it's, you know... We can find ways for people to be more physically active that can, can accommodate every disability, can accommodate every level of fitness, can accommodate-

Dr. Rangan Chatterjee 1:21:32 Yeah

Dan Lieberman 1:21:32 ... you know. But, but we, we, as a society, we've been very uncreative about it. We're, we're, we're, um, we're not really willing to put in the time and the money and the effort to make it happen.

Dr. Rangan Chatterjee 1:21:43 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 1:21:56 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 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, bzz, 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 1:23:13 Mm-hmm

Dan Lieberman 1:23:13 ... 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, bzz, 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 mot- most of our existence. If you're struggling-

Dr. Rangan Chatterjee 1:23:52 Mm

Dan Lieberman 1:23:52 ... 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 1:24:02 Yeah.

Dan Lieberman 1:24:02 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 1:24:15 Yeah

Dan Lieberman 1:24:15 ... 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. Um, 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 1:24:50 Yeah. 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 1:25:30 Exactly.

Dr. Rangan Chatterjee 1:25:30 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 it not... And, 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 [laughs] to take the stairs if you don't have to?

Dan Lieberman 1:26:19 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, so 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 1:26:44 Mm-hmm.

Dan Lieberman 1:26:44 And 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 1:27:01 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 1:27:12 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 1:27:20 Mm-hmm.

Dan Lieberman 1:27:21 Turns out the average hunter-gatherer, because we're always told that we sit too much, right? And that's, you know, 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," 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 make... And then they think that, well, they're lazy. There's something wrong with them. They're actually normal, right?

Dr. Rangan Chatterjee 1:28:31 Yeah.

Dan Lieberman 1:28:31 They're completely normal human beings, and we h- 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 it '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 1:28:59 Yeah.

Dan Lieberman 1:28:59 We consider it a pill, right? And nobody likes to take pills.

Dr. Rangan Chatterjee 1:29:02 [laughs]

Dan Lieberman 1:29:02 Nobody likes a... 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 1:29:13 Yeah, yeah

Dan Lieberman 1:29:14 ... 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 1:29:19 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 1:29:45 Yeah. I think the key word is discretionary. You don't have to do it.

Dr. Rangan Chatterjee 1:29:48 Discretionary.

Dan Lieberman 1:29:48 It's discretionary physical activity for the sake of health and fitness.

Dr. Rangan Chatterjee 1:29:51 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 1:30:16 So it is a side... I mean, you're right. They, they do it because they have to, right?

Dr. Rangan Chatterjee 1:30:21 Mm.

Dan Lieberman 1:30:21 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 1:30:26 Yeah.

Dan Lieberman 1:30:26 It doesn't... There's no Uber Eats in the Paleolithic, right?

Dr. Rangan Chatterjee 1:30:29 [laughs]

Dan Lieberman 1:30:29 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 evolve 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 1:31:13 Mm.

Dan Lieberman 1:31:13 And let me tell you, uh, you know those sh- those shows on TV where you watch chimpanzees and they're doing all kinds-

Dr. Rangan Chatterjee 1:31:18 [laughs]

Dan Lieberman 1:31:18 ... 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 1:31:42 Mm-hmm.

Dan Lieberman 1:31:43 And, uh, so chimpanzees turn out to be basically couch potatoes. They're incredibly inactive. A typical chimpanzee walks two to three kilometers a day, takes bas- 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 1:32:23 Mm-hmm.

Dan Lieberman 1:32:24 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 1:32:47 Mm-hmm.

Dan Lieberman 1:32:47 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 1:33:10 Mm-hmm.

Dan Lieberman 1:33:10 And what are they doing? Well, I mean, they're sort... 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 th- 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 1:34:31 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 1:34:41 Exactly. We call that a mismatch in evolution.

Dr. Rangan Chatterjee 1:34:43 Yeah.

Dan Lieberman 1:34:43 It's an evolutionary mismatch. Just like we never evolved not to breathe, right? [laughs]

Dr. Rangan Chatterjee 1:34:47 Yeah.

Dan Lieberman 1:34:47 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 1:34:58 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 1:35:40 Yeah.

Dr. Rangan Chatterjee 1:35:41 Um, so, so speak to that a little bit.

Dan Lieberman 1:35:43 Yeah.

Dr. Rangan Chatterjee 1:35:43 'Cause that, that's really interesting.

Dan Lieberman 1:35:44 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 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 1:36:21 But they're not nursing and breastfeeding-

Dan Lieberman 1:36:22 Yeah

Dr. Rangan Chatterjee 1:36:23 ... are they? So I guess they've got-

Dan Lieberman 1:36:24 Yeah, and also their, you know, their kid's not clinging onto them as much, right?

Dr. Rangan Chatterjee 1:36:27 Yeah.

Dan Lieberman 1:36:27 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 1:37:26 Mm-hmm.

Dan Lieberman 1:37:27 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 kind of keep them going, right? And so we can, we can enable us to live, we have reasonably long he- lifespans-

Dr. Rangan Chatterjee 1:37:49 Mm-hmm

Dan Lieberman 1:37:49 ... 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 1:38:10 And, and how does that compare to these hunter-gatherer populations that you've spent so much time with?

Dan Lieberman 1:38:14 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 non-existent or very, very, very rare. It's very... It's hard to diagnose these diseases, obviously, out in the, in the, in the field.

Dr. Rangan Chatterjee 1:38:30 Uh, and have you been to Kenya annually since you were in your 20s? Is that right?

Dan Lieberman 1:38:33 Oh, gosh, I've been going to Kenya almost every year since 1987.

Dr. Rangan Chatterjee 1:38:37 That is a long time. And other countries in Africa.

Dan Lieberman 1:38:41 Yeah.

Dr. Rangan Chatterjee 1:38:41 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 kind of fascinates 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 1:39:19 We don't have that much data on hunter-gatherer diets.

Dr. Rangan Chatterjee 1:39:22 Okay.

Dan Lieberman 1:39:22 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 1:39:34 Mm-hmm.

Dan Lieberman 1:39:34 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 1:39:43 Yeah.

Dan Lieberman 1:39:43 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. That's, that's probably one of the problems with the paleo diet. Um, but I would say that if you took an average, um, about 30% of the calories in a typical tropical subsistence population-

Dr. Rangan Chatterjee 1:40:04 Mm

Dan Lieberman 1:40:04 ... comes from meat. Um, and but also that meat is very different from the meat that we eat-

Dr. Rangan Chatterjee 1:40:09 Yeah

Dan Lieberman 1:40:09 ... in the West. That meat has got lower levels of saturated fat. It's, uh... It's a, it's a wholly... It's a different beast, basically. So-

Dr. Rangan Chatterjee 1:40:16 Yeah

Dan Lieberman 1:40:16 ... uh, so the meat is not even the same.

Dr. Rangan Chatterjee 1:40:19 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. 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 1:41:16 And good for them.

Dr. Rangan Chatterjee 1:41:17 And good for them.

Dan Lieberman 1:41:18 Yeah. [laughs]

Dr. Rangan Chatterjee 1:41:19 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 1:41:29 Maybe they're watching this podcast.

Dr. Rangan Chatterjee 1:41:30 Yeah. They, they-

Dan Lieberman 1:41:31 [laughs]

Dr. Rangan Chatterjee 1:41:31 Someone will probably be watching it now-

Dan Lieberman 1:41:33 Exactly

Dr. Rangan Chatterjee 1:41:33 ... or listening to music-

Dan Lieberman 1:41:34 Right

Dr. Rangan Chatterjee 1:41:34 ... 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 1:42:20 Well, I think what you're saying is that w- we have this mind-body dualism-

Dr. Rangan Chatterjee 1:42:25 Mm

Dan Lieberman 1:42:26 ... in, in, in, 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 1:42:35 Mm.

Dan Lieberman 1:42:35 And, you know, I'm sitting in a chair here. I could have taken the subway here, et cetera, et cetera-

Dr. Rangan Chatterjee 1:42:40 Yeah

Dan Lieberman 1:42:40 ... and the, 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, there's nothing wrong with industrialization or medicalization-

Dr. Rangan Chatterjee 1:43:13 Yeah

Dan Lieberman 1:43:13 ... 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? Because when you-

Dr. Rangan Chatterjee 1:43:26 Yeah

Dan Lieberman 1:43:26 ... play a game of football or something, right, you're... You now have a purpose that's-

Dr. Rangan Chatterjee 1:43:31 Yeah

Dan Lieberman 1:43:31 ... And you... And, and most people don't think ofOr going for a walk with a friend or playing a game of sport. They don't, don't often think of it as exercise, right? They think of it as, as y- 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 1:43:51 Yeah

Dan Lieberman 1:43:51 ... be more physically active. Give ... Make it, make it part of our lives. So go for a walk with somebody.

Dr. Rangan Chatterjee 1:43:56 Yeah. I, I'm not at all criticizing that. I, I myself will do that, uh-

Dan Lieberman 1:44:00 Yeah

Dr. Rangan Chatterjee 1:44:00 ... from time to time, right? So I get it.

Dan Lieberman 1:44:02 Me too. Yeah.

Dr. Rangan Chatterjee 1:44:03 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 kinda think about this mind-body separation a lot, and I think two things. I think w- w- 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 1:44:52 It's a form of prayer.

Dr. Rangan Chatterjee 1:44:53 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 1:46:08 Absolutely. Yeah. I mean, um, there's a wonderful argument actually that, that the origins of science comes from tracking.

Dr. Rangan Chatterjee 1:46:15 Mm.

Dan Lieberman 1:46:15 Because you're making hypotheses. You're not only observing nature, right? Because, 'cause you need to, right? You're trying to f- follow an animal, right? But you're also, you're also thinking. You're also trying ... You're making guesses. So I think it went to the right. Well, 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 1:46:40 Yeah.

Dan Lieberman 1:46:40 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 1:47:01 Mm.

Dan Lieberman 1:47:01 And, um, and when you get high, right, um, what happens? You have a increased sensory perception.

Dr. Rangan Chatterjee 1:47:09 Yeah.

Dan Lieberman 1:47:09 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 'cause right by the end, and I remember th- saying to myself, "Wow, Big Ben is really big." You know? And, and I was having, like, experiences like that.

Dr. Rangan Chatterjee 1:47:35 Yeah.

Dan Lieberman 1:47:35 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. 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 1:47:50 Yeah.

Dan Lieberman 1:47:50 And, and I remember the, this guy named Dan Tunstall-Pedoe, who's the medical director of the marathon. I 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 1:48:02 Right.

Dan Lieberman 1:48:02 It's like, "Oh, yeah, I guess I do."

Dr. Rangan Chatterjee 1:48:04 Right.

Dan Lieberman 1:48:04 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's helping you get more ... You know, your ... Everything you're seeing is now is 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 1:48:22 'Cause I guess the point of running, and, and I appreciate that you, you do mention that there are these long races that, that 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 1:48:38 Correct.

Dr. Rangan Chatterjee 1:48:38 So therefore it makes sense that we would have heightened awareness and sensations and maybe sounds.

Dan Lieberman 1:48:46 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 ear- headphones, and I listened to some very-

Dr. Rangan Chatterjee 1:48:58 Yeah

Dan Lieberman 1:48:58 ... 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 1:49:05 Yeah.

Dan Lieberman 1:49:05 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 1:49:13 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 1:49:30 Never.

Dr. Rangan Chatterjee 1:49:32 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 1:49:43 Sure

Dr. Rangan Chatterjee 1:49:43 ... 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 1:49:50 Yeah, that's my day job really. [laughs]

Dr. Rangan Chatterjee 1:49:52 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 1:50:31 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 1:50:50 Mm-hmm.

Dan Lieberman 1:50:50 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've, 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 1:51:20 Mm-hmm

Dan Lieberman 1:51:21 ... uh, a, a less industrial life. Um-

Dr. Rangan Chatterjee 1:51:23 Yeah

Dan Lieberman 1:51:24 ... 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 1:51:47 Yeah

Dan Lieberman 1:51:47 ... 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, they're not normal, right? And, and, and, and just perceiving that, thinking about that has 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. There'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 1:52:44 Mm-hmm

Dan Lieberman 1:52:44 ... 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 1:52:54 Yeah.

Dan Lieberman 1:52:54 It's stunning.

Dr. Rangan Chatterjee 1:52:55 You mentioned footwear then. Um, you're probably regarded, I think, as one of the, the godfathers of the minimalist-

Dan Lieberman 1:53:03 [laughs]

Dr. Rangan Chatterjee 1:53:04 ... shoe movement. I don't-

Dan Lieberman 1:53:05 I'm the, the barefoot professor. Yeah. [laughs]

Dr. Rangan Chatterjee 1:53:06 Yeah. I don't know how that, how that ha- uh, sits with you.

Dan Lieberman 1:53:10 [laughs]

Dr. Rangan Chatterjee 1:53:10 But, um, let, 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 ... There, there are trade-offs. 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 1:53:43 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 1:53:51 Mm.

Dan Lieberman 1:53:51 Just about everything on the planet.

Dr. Rangan Chatterjee 1:53:52 Yeah.

Dan Lieberman 1:53:52 There, 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 1:54:03 Yeah.

Dan Lieberman 1:54:03 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're, 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 that 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 kind of 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 1:54:52 Are you talking about walking on the beach without shoes on?

Dan Lieberman 1:54:54 Without, barefoot.

Dr. Rangan Chatterjee 1:54:55 Yeah.

Dan Lieberman 1:54:55 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 ha- 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 1:55:09 Yeah

Dan Lieberman 1:55:09 ... right, you're now, your foot muscles have to do less work.

Dr. Rangan Chatterjee 1:55:12 Yeah.

Dan Lieberman 1:55:12 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 1:55:17 Mm

Dan Lieberman 1:55:17 ... 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 1:55:34 Yeah

Dan Lieberman 1:55:35 ... 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 the technology.

Dr. Rangan Chatterjee 1:55:46 Yeah.

Dan Lieberman 1:55:46 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 area 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.

Dr. Rangan Chatterjee 1:56:09 Mm.

Dan Lieberman 1:56:09 Um, 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 1:56:14 Yeah

Dan Lieberman 1:56:14 ... 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 1:56:22 Yeah.

Dan Lieberman 1:56:22 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, 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 sh- supportive, cushioned shoes that, um, that have effe- 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 'cause it hurts.

Dr. Rangan Chatterjee 1:56:56 Yeah.

Dan Lieberman 1:56:56 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 1:57:06 Yeah

Dan Lieberman 1:57:06 ... '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 1:57:26 Okay. I've got so many questions.

Dan Lieberman 1:57:27 That's a long, long answer. Sorry. But it's a big question.

Dr. Rangan Chatterjee 1:57:29 No, no, no, not at all. I mean, um, regular listeners, uh, to, to this podcast will know what a fan I am of minimal issues. I personally have been wearing them since 2012 now, so 12, almost 13 years, like pretty much exclusively. I see you've got some VIVO- VIVOBAREFOOT on like I have at the moment. Um, 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 1:58:35 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 1:58:56 Mm

Dan Lieberman 1:58:56 ... 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, 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 1:59:42 Mm.

Dan Lieberman 1:59:42 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 1:59:49 Okay.

Dan Lieberman 1:59:49 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 2:00:01 Mm

Dan Lieberman 2:00:01 ... 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 2:00:13 Yeah

Dan Lieberman 2:00:14 ... things can happen. It's awful. Plantar fasciitis sucks. I've had plantar fasciitis [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 started doing it maybe 2007, 2008.

Dr. Rangan Chatterjee 2:00:43 Mm-hmm.

Dan Lieberman 2:00:44 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, a, a f- 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, the 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 2:01:21 Yeah.

Dan Lieberman 2:01:21 So, so those are two good reasons to have, avoid a flat foot, avoid fallen arches. And, and I think there's a third reason, which is that it's, it's a proxy, right? Um, for using your body, um, as we evolved to use it.

Dr. Rangan Chatterjee 2:01:37 Yeah.

Dan Lieberman 2:01:37 And, um, there are all kinds of muscles in our bodies 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 2:01:52 Yeah.

Dan Lieberman 2:01:53 Everything is connected. Everything is connected.

Dr. Rangan Chatterjee 2:01:55 For sure.

Dan Lieberman 2:01:55 You can't, you can't just strengthen this and not strengthen that. Everything should be strong.

Dr. Rangan Chatterjee 2:02:00 Yeah. If I just share my own experience with, uh, transitioning from, you know, regular modern cushioned shoesI remember when I first went into minimal 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 2:02:39 Exactly.

Dr. Rangan Chatterjee 2:02:40 Okay? Th- 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 2:02:47 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 it, 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 2:03:03 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 2:03:22 Oh, absolutely. So, uh, my previous book, The Story of the Human Body, I came up with a term for this. I c- come with what I call devolution. What happens is that we treat the symptoms rather than the causes of problems that are mismatches-

Dr. Rangan Chatterjee 2:03:34 Mm-hmm

Dan Lieberman 2:03:34 ... 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, it, things to get worse, right?

Dr. Rangan Chatterjee 2:03:43 Mm-hmm.

Dan Lieberman 2:03:44 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 2:03:52 No, but the principle is there.

Dan Lieberman 2:03:53 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 2:04:14 Yeah

Dan Lieberman 2:04:14 ... go barefoot, and all my problems will be solved. You know, my teeth will be whiter. Girls will like me more," or 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 2:04:39 For sure

Dan Lieberman 2:04:40 ... sometimes these treatments. And, and [laughs] I remember my, uh, my wife, I, who also likes... 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 2:04:53 Right.

Dan Lieberman 2:04:53 But, um, she went to a podiatrist or a orthopedist in, at the Harvard Medical S- Service, and, 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, 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 you, you're, you're not counting all the people who are also wearing these shoes who you're not seeing."

Dr. Rangan Chatterjee 2:05:26 Yeah.

Dan Lieberman 2:05:26 [laughs] And he's like, "Oh, huh, I never thought about that." Um.

Dr. Rangan Chatterjee 2:05:30 It's a good point, isn't it?

Dan Lieberman 2:05:31 [laughs] Yeah.

Dr. Rangan Chatterjee 2:05:32 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 shoe. They go to the shops in them. Their... 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 2:06:20 If it ain't broke, don't fix it.

Dr. Rangan Chatterjee 2:06:21 Yeah. So I get that. And 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 2:06:42 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? The, what's the most fundamental form of physical activity? It's not running. It's walking.

Dr. Rangan Chatterjee 2:06:57 Walking.

Dan Lieberman 2:06:57 And I expected to see people start applying the, the tools that we pu- you know, the arguments-

Dr. Rangan Chatterjee 2:07:03 Mm

Dan Lieberman 2:07:03 ... 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 2:07:23 And what, and what does it show?

Dan Lieberman 2:07:25 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 2:07:52 Mm.

Dan Lieberman 2:07:53 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 a- an acorn or something like that and not hurt me. But I could-

Dr. Rangan Chatterjee 2:08:05 Right. When you say you were running barefoot, do you mean with minimalist shoes-

Dan Lieberman 2:08:08 No, barefoot

Dr. Rangan Chatterjee 2:08:08 ... or completely barefoot?

Dan Lieberman 2:08:09 Completely barefoot.

Dr. Rangan Chatterjee 2:08:10 Okay. So-

Dan Lieberman 2:08:11 Yeah.

Dr. Rangan Chatterjee 2:08:11 Real bare foot.

Dan Lieberman 2:08:12 When I say barefoot, I mean barefoot. Right.

Dr. Rangan Chatterjee 2:08:13 Got it.

Dan Lieberman 2:08:14 And I was ... So I was, um, you know, I 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 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 2:09:00 That's amazing.

Dan Lieberman 2:09:01 And so we did these studies in Kenya. We looked at people who had thick calluses, because they had 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 2:09:21 Mm.

Dan Lieberman 2:09:22 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, uh, when I was, when I was doing a lot of barefoot running ... I don't run barefoot pretty much anymore, because 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, there's a few streets I run down.

Dr. Rangan Chatterjee 2:09:41 Mm.

Dan Lieberman 2:09:41 And I often in the morning I would see this woman who was ... She has, um, she had two beautiful dogs. I remember 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 2:10:19 If you enjoyed that conversation, then I think you are really going to enjoy this one that I've picked out especially.

Guest 2:10:25 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