"It Only Takes 12 Hours!" - Burn Stubborn Fat, Starve Disease & Stay Young | Dr. Jason Fung

Dr. Jason Fung 0:00 I used to think, you know, weight loss is just about willpower. It's about calories in, calories out. The energy balance equation is always true, but people always misinterpret it to mean that just eating fewer calories leads to body fat loss. It does not. [upbeat music]

Dr. Rangan Chatterjee 0:20 You have been sharing health information with your patients, with people all over the world, for coming up to a decade now. You've helped so many people improve their lives, improve their health. With all that experience, with all that knowledge, I wanted to start by asking you, what are some of the daily things that people can think about doing that's gonna help them feel better, improve their health, reduce weight if they need to, but also reduce the risk of getting sick in the future?

Dr. Jason Fung 0:51 Yeah, I think there's a few things. I mean, one is sort of to stop a lot of the sort of snacking that goes on. Um, you know, for a long time, people sort of said, "Oh, you should eat sort of 10 times a day," sort of thing, right? You know, make sure you get your snacks and stuff. And I think it really sort of drives us in the wrong direction, uh, based on, uh, you know, the people who need to lose weight because unfortunately, that's the more, you know, that's the majority of people these days. And this idea that you should sort of eat all the time and it being healthy is probably one of the most, uh, sort of damaging things that we've done to people. It's not natural, it's not what we used to do, it's not- it's what we haven't, like we haven't done that for, you know, most of, most of our history. It- it's only been in the last sort of 30 years that people thought, "Well, you should eat six to eight times a day." Most of the time, it was sort of two to three times a day maximum, um, with stipulations that you really shouldn't eat more than that. And then now all of a sudden people are like, "Oh, yeah, you should eat so, you know, all the time to lose weight." I'm like, how does that even work, right? Like, from a physiologic standpoint, when you eat, you're not losing [laughs] weight. You cannot be. It's impossible. So, you know, this idea that, oh, you have to, you have to do that, it- it- it's sort of a, a very, very modern idea that's been presented as scientific and all that sort of stuff, and I think it's really damaging because then people don't get the right idea that, hey, you can leave your body and, you know, it'll figure out where it's gonna get its energy from without completely screwing up the system sort of thing. So I think that's, that's one of the things I've sort of focused on mostly, is trying to increase that sort of fasting period, or if you're trying to lose weight, using intermittent fasting, that kind of thing. It's, it's, it's one of the things that I think makes no sense to me whatsoever.

Dr. Rangan Chatterjee 2:55 Yeah.

Dr. Jason Fung 2:56 The next thing, uh, I think it's, it's important to do is sort of put it on the schedule. That is, even things like eating, it should be sort of scheduled. It's all that unscheduled snacking and stuff that, that really derails people. So you're walking by and you say, "Hey, there's a, you know, a coffee shop. I'm gonna get a coffee." Then you see the, go in the coffee, and then you smell the donuts, and then, like, before you know, you've got the donuts, right? So the problem is that you've got all these, uh, periods of time where you've got unscheduled sort of, uh, opportunities to eat, and they're never really good for you. You're walking and you're in the office, somebody has a bowl of candy out, so you go and get some candy. You go to the, you know, it was never on the schedule. You have a meeting, all of a sudden somebody's, uh, ordered a plate of cookies, and before you know it, you've eaten cookies, right? So there's all this sort of scheduled stuff, uh, like unscheduled stuff. And so you really wanna just put a, make sure, y- you know, when you're eating, you're, you make sure you're... It's sort of like mindfulness, right? You're, you're, you're deliberately scheduling a time to eat, and every other time, don't eat, right? And it, it sort of goes hand in hand with this idea that we should eat all the time to lose weight. We think that there's no cost to it. Um, or, you know, maybe we're the ones ordering [laughs] the plate of cookies for, for the afternoon meeting, right? And it's like, it's not necessary. It never was necessary. It's not doing anybody any favors. So, you know, make sure that when you're eating, you know, it's sort of, it's, it's sort of on the schedule. Like, if it's not on the schedule, then you shouldn't be eating. And it's, it's, it's, it's the same idea as mindfulness, uh, behavior.

Dr. Rangan Chatterjee 4:38 I love the idea of scheduling when you're going to eat. It almost feels like a revolutionary act in the 21st century because there's such, there's such food availability all the time. You know, we- we're always surrounded by food, tempted by food, and just this very simple idea that put when you're going [laughs] to eat on the schedule, uh, I think for many people, it, it may be the first time they've ever heard that before.

Dr. Jason Fung 5:06 Yeah, it's, it's sort of, it's what your default is, right? So most of the time, up until, say, the '90s, the default was not eating, so therefore you scheduled when you ate, breakfast, lunch, and dinner. All of a sudden, um, based on no science really, um, we thought we should eat constantly. From the minute you get up to the minute you go to bed, you hear constant refrains. Well, you know, always eat breakfast, never skip breakfast, start eating immediately, and then have bedtime snacks, and have snacks. And y- you think about in, I don't know in the UK, but in Canada, for example, uh, if you send your kids to school, they get, like, morning snacks, they get after-school snacks, they get snacks when they go on the bus. You know, they, then they play, uh, you know, sports, and somebody wants to give them snacks in between, you know, to give them energy. And it's like, you know, they have plenty of energy whether you give them sugar or not. And so the default all of a sudden became eating. So, you know, it was, it was strange because we went from a default of not eating, you have to decide when you're gonna eat, to eating all the time and descen- [laughs] deciding when you're not going to eat, which is bizarre.

Dr. Rangan Chatterjee 6:18 Yeah.

Dr. Jason Fung 6:19 So, you know, it, and, and not healthy, because if your baseline is to eat, then you're gonna gain weight. It's, it's unfortunately, there's no way around it.

Dr. Rangan Chatterjee 6:29 You are a big proponent of fasting, intermittent fasting, and you've done a lot to spread knowledge of that throughout the world over the past few years. Many people these days are trying to experiment with some form of fasting. In your experience, and I know you've got, you know, years of practical experience doing this with real live patients with busy lives, you know, busy jobs, kids to look after, all those kind of things, what are some of the common mistakes that people often make when they try and do some form of intermittent fasting?

Dr. Jason Fung 7:07 Um, probably the biggest one is sort of overeating when you fast. Like, thinking that just because you didn't eat for a period of time, that gives you sort of carte blanche to eat whatever you want afterwards. Um, and sort of there's two important factors in weight losses. One is the foods that you eat, and we talk about this all the time. That's your diet, right? What you eat when you decide you want to eat. Uh, so you know how people are paleo and keto and vegan and whatever. It's, th- there's plenty of different diets, and we argue about that all the time. Um, but what, what a lot of people don't talk about is sort of the time you spend not eating, right? And that's your period of fasting. How long should it be? How often should you eat? Those are just as important questions, 'cause it's more than half of your day is, should be spent not eating. So, um, you know, if you, if you get that part right, that is, you spend a period of the day not eating, 16 hours or 24 hours or whatever you decide, it, it still doesn't mean that you can just eat whatever you want. And there's been several studies using this exact sort of, um, sort of overfeeding strategy. That is, "Oh, we'll fast for 16 hours," and then let people eat whatever they want. Well, it's, it's a very unsuccessful strategy. You want to eat still healthy, still sort of good, nutritious whole foods, and combine the fasting. It's not sort of like y- there's sort of, like, two levers, right? You want them both going in the right direction. You don't wanna go one up and one down. That's just gonna make it ineffective. So, you know, and, and that's one of the things that people don't understand, because there are some rat studies, for example, that said, well, rats, y- you let them eat whatever they want, and as long as they fast for a period of time, they stay underweight, so therefore, that should apply to humans too. You can eat whatever you want. That is, if you fast 16 hours, you can eat junk food and fast food and McDonald's and all this sort of stuff. It's like, no, you can't. [laughs] The point is, when you're fasting, all you're trying to do is let your body use the calories that you've stored away as body fat. That's all it is. So body fat is nothing more or less than a storage form of calories, right? You take in food energy in the form of calories, and your body stores some of that away. That's when you eat. When you don't eat or when you're fasting, then your body is going to use the store of calories that you've put away, right? That's why you don't die in your sleep every single night, because your body has the ability to store some of those calories away. So that's all it is. So it, it always boggles my mind that people, experts are saying, "Oh, you know, intermittent fasting is bad for you, and it's, like, not natural." And it's like, it's the most natural thing in the world.

Dr. Rangan Chatterjee 9:53 Yeah.

Dr. Jason Fung 9:53 You're supposed to be cycling. That's why you have this word, break fast, breakfast. You're supposed to fast. Otherwise, you can't break your fast. But you're supposed to feed and you're fast. And, and if you ask your grandmother, she, she would say something like, "Well, you know, you just gotta give your ti- your body some time to digest the food that you've eaten."

Dr. Rangan Chatterjee 10:14 Yeah. It, it's funny how culture has changed so much just in the last 30, 40, 50 years, where this idea of eating all the time has become just so prevalent. And it's really interesting what people actually do. You know Professor Satchin Panda from the Salk Institute. I know when I last spoke to him, he was sharing information with me from his app that people are tracking how often they're eating for, and he said 50% of non-shift workers in the US are eating pretty much over a 15-hour period each day. Now, technically it was 14 hours 45 minutes, but basically 50% [laughs] are eating over 15 hours. And he said under 10% of people that they were tracking were eating in under a 12-hour window. Now, if we compare that to 100 years ago, this is so abnormal, isn't it? This is, this is so not how we have lived for, for most of our evolution. And I guess the question then is, you know, why is this problematic? And when we say fasting or when you use the term fasting, what do you mean by it?

Dr. Jason Fung 11:28 Yeah. And, and it's really just, fasting is just any period of time that you're not eating. I mean, if you think about the 14 hours 45 minutes, if you s- if you wake up at 8:00 AM and you start eating immediately, you're eating until 10:45 PM, right? That's, that's basically your entire waking day, right? Minus brushing your teeth sort of [laughs] thing, right?

Dr. Rangan Chatterjee 11:52 Yeah.

Dr. Jason Fung 11:53 It's a ridiculous amount of time to be eating, and that's the average. So, you know, when y- you talk about this, how did, you know, how did this happen and why is it so bad, well, I think I have my theories about why it ha- happened, but the reason it's so bad is that your body really exists in one of two states. It's either in the fed state, which is you're eating, insulin is high, which is telling your body, "Please store some of these calories that are coming into your body, because you're gonna need them for when you're not eating." Or it's in the fasted state, which is insulin is low, you're not eating, and your body says, "Hey, I need calories. Please take them from my storage." Right? And so it's no different than a refrigerator, for example. You go to the grocery store, you have too much food, you put it in the fridge, right? So now think about it this way. If you now go to the store five or six times a day, and all the time you're putting food in your fridge, putting food, pretty soon your fridge is gonna be full. Then somebody says, "Well, in order to empty your fridge, you need to go to the store more often." It's like, does that make any sense? When you're eating, you're telling your body, like you are literally telling your body, "Please store some of these excess calories into storage. Put it into storage." 'Cause that's what the insulin does. It's neither good nor bad, it's just its job. So because you're stimulating it all the time, you're telling your body all the time to do it. For 14 hours and 45 minutes [laughs] of every day, you're telling your body to do that, and it's actually more, because of course your stomach actually holds some of the food and slowly sort of pushes it out. So it's not 14 and 45 that your body is in the fed state. It's actually hours longer than that. So the point is simply this, like we, we try and complicate things so much all the time, but it's very simple. When you're eating, you're storing calories. When you're not eating, you're using calories. That, that's all it is. And, and that's natural, and it's normal, and you can handle it. Like, people think it's so, um, you know, you need to eat 2,000 calories in a day. You shouldn't cut your calories, for example, uh, like what, you know, if you fast the entire day. Well, if you're worried about those 2,000 calories, well, what about the 100 or 200 or 300,000 calories that you have stored currently on your body? Like, why would you worry about the 2,000? Just like the refrigerator. If you don't go to the store one day, are you going to be really badly off? Well, your fridge is overfilled. You have way too much stuff in the fridge. Just eat something from the fridge. That's the same thing. If you don't eat, your body has a, you know, 300,000 calories of body fat. Your body's gonna use it. Or you're diabetic, you have blood sugar sort of just spilling out from everywhere. Your body's going to use some of that sugar, because it's a source of energy. So what's wrong with that? How is that bad in any sense [laughs] -

Dr. Rangan Chatterjee 14:53 Yeah

Dr. Jason Fung 14:53 ... of the word? You're simply letting your body use it for what it was designed for, and that's the whole point of fasting, was, wh- which is why it always boggles my mind that you see experts saying, "Oh, you know, uh, intermittent fasting's so bad for you." But you have... And, and there are certain circumstances, of course. If you're malnourished, if you're underweight, you know, sure. Absolutely. But if you're overweight, if you're type 2 diabetic, that's actually exactly what you want your body to do.

Dr. Rangan Chatterjee 15:20 Yeah. Let's expand this beyond weight loss, because one of the things that pulls all of your work together, for me at least, is that we have overly focused on calories and not focused enough on hormones. And it's easy to talk about fasting and burning body fat in the context of someone who might have type 2 diabetes or someone who is carrying excess fat and considers themselves to be overweight, but this goes beyond weight, doesn't it? This is actually a very helpful practice for people who want to be in optimal health, have more energy, yes, have a good body weight, but also reduce the risk of getting sick in the future.

Dr. Jason Fung 16:06 Yeah, absolutely, because if you think about it, like it's, it's a balance, yeah, right? You eat, you store calories. You don't eat, you use those calories, right? And you wanna keep those in balance, so 12 hour, 12 hours is perfect. If you think about a typical sort of 1960s, 1970s, 'cause, and I, a- and you know, I choose that time because it's before the obesity epidemic, and people aren't really watching their diet particularly. People are eating white bread and jam and, you know, stuff like that, right? Um, uh, but if you think about it, you know, you ate breakfast maybe 8:00 before school, and then you had dinner maybe around 6:00. That's a 10-hour eating window, and 14 hours of fasting. And literally everybody did that every single day without even thinking about it. So was it hard? No, because that was sort of your baseline. And the, the, the point is that it's not, um, it's not, neither difficult. It's just about your habits. And then, um, you know, then all of a sudden, uh, people switched and changed. But before that, you would hear things like, you know, if you wanted an after-school snack, your mom would say, "No, you're gonna ruin your dinner." If you want a bedtime snack, she'd say, "No, you should've ate more at dinner." Right? So there was ne- not this tolerance of snacking. It was sort of this occasional thing that you did once in a while, but rarely. It's an indulgence, right? And then it became every day. So, so, you know, my kids, when they went to school on a trip, for example, a, a bus trip, right? S- they'd go on the bus, and you'd get this note [laughs] from the school which would say, "Please send two snacks with your child." [laughs] And I'd be like, "Why? Are they not eating lunch, or am I not feeding them dinner? Is that why [laughs] they need a snack?" It's like, my goodness. And, and, and, and then we, so we teach them that it's, you have to snack all the time, and then we blame them for gaining all this weight, and then tell them that, "Hey, it's your diet. It's your lack of willpower." And it's like, well, you know, we focused on the wrong things. And, and you might say i- it was all very inadvertent, I think. It wasn't that anybody deliberately meant to do that. It, it all came back to sort of the, the dietary guidelines, which was in the '70s, people said, "You know, you should eat ultra, ultra, ultra low fat." And in order to do that, the government, the United States government, encouraged people to eat processed food because you could process the fat out of it and put other things, mostly carbs, because fat, fat and protein tend to go together. And so instead of eating, say, a typical breakfast of eggs and bacon, which would keep you full until lunch, they'd eat two slices of white bread and jam and some sugary cereal. The problem with that, and we know this of course, [laughs] is that insulin spikes up very high, glucose spikes up very high because they're all very highly refined carbohydrates. Then it crashes, so by 10:30 you're just starving. So then you go get yourself a low-fat muffin, and then the same thing happens, right? Your, your, your, your ins- glucose spikes are very high, your insulin spikes up very high, and, and then, and then it's gone. So people started eating more frequently because they were basically just eating a whole bunch of refined carbohydrates. Then they said, "Well, I'm eating six times a day when I used to eat three times a day. But since I'm eating super low fat, this must be a good thing." It never was a good thing, of course. It was just a by-product. Now of course, we sh- we know we shouldn't be eating a whole pile of refined carbs, like right away. But back then, two slices of white bread and, and strawberry jam was perfectly acceptable. Very low fat. Almost zero fat, in fact. All sugar, all refined carbs. So I think that's sort of how it came about, because of this, uh, sort of insistence that we eat low fat, low fat, low fat. Which unfortunately wasn't like more beans, it was refined, highly-

Dr. Rangan Chatterjee 20:02 Yeah

Dr. Jason Fung 20:02 ... refined carbs is what replaced the fat in our diet. But then the inadvertent thing was that even as we moved away from those refined carbohydrates, so we started acknowledging, "Hey, there's healthy fats. Hey, you should eat nuts. Hey, you should eat whole grains." Uh, even as we moved away from those refined carbs, we never moved away from the fact that we're just eating constantly. And of course, our institutions have changed to allow all that, right?

Dr. Rangan Chatterjee 20:28 Yeah.

Dr. Jason Fung 20:28 So our habits have changed. You have, you're, it, it's acceptable to eat at your desk, it's acceptable to eat in the movie theaters, it's acceptable to eat in front of the TV, it's acceptable to eat while you're walking. Like, all of those things would've been super frowned upon. If you went to the office and you were eating at your desk in the '70s, people would be like, "What the heck are you doing? Like, there's a place to eat, and it's not at your desk. Go eat somewhere else." But because everybody was hungry [laughs] all the time, you know, you got this 2:30 sna- I mean, you've been to, you've been to meetings, like medical meetings, right?

Dr. Rangan Chatterjee 21:06 [laughs]

Dr. Jason Fung 21:07 Like, my God. It's like, okay, so you'd have a full breakfast, then at 10:30 they roll out the, you know, the granola bars and stuff. And that die- that's at 10:30 AM. You just ate a huge breakfast at, like, 8:00 AM. And then you have lunch, and then you know at 2:30 there's a nutrition break, right, where they roll out muffins and cookies and stuff, right? And then you go eat dinner. It's like, these are for doctors, like you and me, and this is at every single meeting you go to. American Heart Association, Diabetes Association. Like, you'll go to the Diabetes Association meetings [laughs] and they're rolling out, you know, [laughs] snacks and snacks and snacks.

Dr. Rangan Chatterjee 21:47 Yeah.

Dr. Jason Fung 21:47 It's like, okay, well what's the message here? Eat all the time. It always is.

Dr. Rangan Chatterjee 21:53 And I think that just speaks to culturally how much this has changed. As you say, it's just acceptable now to do this. In fact, if you were hosting a meeting, it would probably be considered rude-

Dr. Jason Fung 22:07 [laughs]

Dr. Rangan Chatterjee 22:07 ... if you didn't provide cookies and biscuits and those sort of things. Do you know what I mean? Very few of us are able to resist societal environmental pressures, which is why what happens at schools saddens me so much because it, it, it literally [laughs] is conditioning kids from a young age to, you know, think, "Oh, I need to snack. I've not eaten for two hours. I need to eat something." Whereas, you know, the truth is we know we don't need to do that, and culturally there's countries where, I think France, it's still there in France, where, you know, snacking is just not that common a acceptable type thing to do. You eat when it's meal times, and you don't sort of eat in between. And when I spoke to Professor Tim Spector on the podcast, he was saying, very similar to you, the impacts of constant snacking, what it does for the gut microbiome, all kinds of things that we just don't need to be eating all the time.

Dr. Rangan Chatterjee 22:59 Now, Jason, one of the central ideas in your work is that chronically elevated insulin is problematic for a variety of different reasons. When was the first time you started to become aware of this as a doctor? And then maybe you could go from there and explain what causes insulin to go up and what happens to us. Why should someone listening to this right now who doesn't have Type 2 diabetes, thinks they're in pretty good health, maybe they've got a little bit of extra fat that they don't want, but they can live with it, why should they care about chronically elevated insulin?

Dr. Jason Fung 23:40 It actually impacts a huge number of, uh, medical conditions. It actually, so if you look at insulin resistance, which is really the same as chronically elevated insulin. They're sort of like two sides of the same coin, right? So it's called hyperinsulinemia, which is basically a word, hyper- means high insulin, and then -emia means in the blood. So hyperinsulinemia bas- just means high blood levels, but insulin resistance, people have heard of, is the same really as hyperinsulinemia. They, they, they do the same thing. And, uh, it really impacts a huge number of conditions such as heart disease, Type 2 diabetes, which can cause then kidney disease, nerve problems, amputations, cancer is related to insulin levels. So there's just all of these chronic conditions that are really the main focus of today's medicine that are made worse by chronically elevated insulin levels. And the point is that you're, you're really not supposed to be in that state. So when, when you look at hormones, and this j- applies to almost all hormones- You're really supposed to have a spike of hormone and then go to low levels. So whether it's thyroid hormone or growth hormone or cortisol or, uh, parathyroid hormone, all of these hormones, they spike and then they go down. So growth hormone, for example, will spike in the morning and then it'll go down, uh, to very low levels, and that's why you have to measure these hormones at certain times of the day and not other times. So you do an AM cortisol in the blood work, for example. Well, insulin's really supposed to be the same. You're supposed to have sort of high levels when you eat, then it's supposed to go down, and then high levels, then it goes down. So you're always supposed to have this sort of, uh, balance between the two. What's really bad is when you have high levels all the time, and that's true for cortisol as well. Cortisol, again, it's not bad for you, it's just a natural hormone, but you're supposed to have it spike up and then go down. When you have it chronically high, it's actually super, super bad for you. This idea that eating all the... You should eat all the time, of course, leads to insulin levels [laughs] being up all the time. And the other problem is that as you move away from fatty foods and stuff, then you're choosing foods that typically spike insulin much higher. So if you're choosing white bread over eggs in the morning, eggs have very little insulin effect and white bread has very high insulin effect. So you're, you know, it's a sort of a double whammy. You're choosing foods that are very high in insulin and, and, and, and if you think about it, so insulin, its job is just tell you... It's a nutrient sensor, so it tells you food is coming in, please store it away. So you choose white bread. So even if it's the same number of calories, say you choose a white bread versus an egg. When you eat that white bread, glucose spikes up, insulin spikes up. When insulin spikes up, it says, "Put all those calories into storage," because that's, that's its job. That's what it's telling you to do. So when you eat that bread, it contains two things. It contains the energy, which is the calories, but it also contains instructions as to what to do with those calories. So you eat the white bread, insulin goes up, all of that energy goes immediately into your storage. Well, now, at 10:30, you have no energy left. Your blood sugars are starting to go very low. So what happens? Your body says, "I need to get more food." Why? Because you've put it all away. It's just like you go to the grocery store and you take the food. Instead of eating some of it, you put all of it into the freezer or the fridge. Well, you have nothing to eat, so then you go out and buy more food, right? It makes no sense. Whereas the egg, the insulin's not gonna go up as high, the energy is now available for you to use all day, and you're not hungry at 10:30 because you still have energy to, to, to do your activities of daily living, right? But the, it was the hormones really that made the difference, and this is the thing [laughs] that I think is really important. When you have two foods, you know, white bread and eggs, which are the same number of calories, the body's response to those calories are completely and utterly different, okay? So one of them spikes insulin, one of them doesn't. So in order to say that they are equal, and you hear this all the time, "A calorie is a calorie. Just count your calories," right? That's how you get stupid ideas like, "Oh, you can eat ice cream for dinner. Just don't eat your broccoli because [laughs] you're, there's 100 calories of broccoli you didn't eat, so you can eat 100 calories of ice cream." Well, that's stupid. It's really, really bad advice that a lot of experts gave out because they're like, "It's the same number of calories." But the hormonal effect is so different, and it's the hormones that tell your body what to do. You take 100 calories in, you can either store it away or you can use it as energy, right? One of them makes you fat and one of them makes you full, gives you energy. Which one do you want to do? Well, you have to choose the 100 calories that don't go straight to fat, which is, you know, the ice cream and, and the white bread and so on, right? And that's the point that everybody misses when they're so focused on calories, and there's so many people out there that are like, "Calories. You're saying calories aren't important." Like, I'm saying [laughs] that there's way more important things than the calories because it's what you do with that energy-

Dr. Rangan Chatterjee 29:00 Yeah

Dr. Jason Fung 29:00 ... not just the total amount of energy.

Dr. Rangan Chatterjee 29:02 Yeah. There's a couple of things there for me. One of the problems with saying whether you're eating ice cream or eggs or salmon or whatever [laughs] it might be, it's the same as long as it's the same amount of calories. Problem number one with that for me is that food is so much more than calories. Food is information. Food has an impact on inflammation. It has an impact on genetic expression. It does so much. It's, it signals so many things in the body which we, we really undervalue when we just say, "How many calories is in that?" firstly. Secondly, I think this idea of calories is worth just exploring in a little bit more depth because, as you say, a lot of people talk about calories in versus calories out. S- s- simple. If you want to lose weight or maintain a healthy weight, you just need to get in a deficit with calories. You know, we have to be burning off more than we're taking in, technically, scientifically. Do you have any insight on that?

Dr. Jason Fung 30:00 Yeah. So the energy balance equation is basically, they say body fat equals calories in minus calories out. That's sort of the, what we all think about, so therefore people say, "Oh, you must be in a caloric deficit." You actually can never be in a caloric deficit because it's a balance equation. There's three variables, body fat, calories in, calories out, and they must balance. So the point is that if you change one of those variables, and everybody forget... I always think there's only two variables, calories in, calories out. No, there's three variables, body fat, calories in, calories out. If you change one of those variables, calories in, it does not mean... There's two other variables. It does not mean that your body fat will decrease because if you decrease calories in- You could also decrease your calories out. That is, your metabolic rate will go down, and your body fat will be unchanged, right? So the energy balance equation is always true, but people always misinterpret it to mean that just eating fewer calories leads to body fat loss. It does not. In fact, almost every study we've done over the last sort of 50, 60 years says that when you simply reduce calories and don't change the sort of composition of your calories, then what happens is that body fat goes down a little bit, but what happens is your metabolic rate goes down more. So if you go from 2,000 calories, for example, you're burning 2,000, you're eating 2,000, you're, you're, you're, you know, in balance. You wanna lose weight now, so you go down to 1,500 calories. That's what everybody says, right? Eat 500 calories less per day. So you cut out the salmon, and you cut out the eggs, but you love bread and ice cream, so you keep your bread and ice cream. You go down to 1,500 calories. There's two possible things that happen. One is that you lose body fat, but two, the other possibility, is your body simply burns 1,500 calories, and your body fat stays relatively unchanged. That does not break the energy balance equation, neither does it break the laws of thermodynamics. In fact, when you look at studies, every study we've done practically over the last 50 years shows that is precisely what happens. You eat 1,500 calories, your body then actually goes down and burns 1,400 calories, and you start to gain weight back. And then when you start to gain weight back because you did the diet all wrong by focusing on calories, people say, "Oh, you know, you weren't trying very hard. You didn't have willpower," and all this kind of stuff, right? And that's the whole problem with, uh, weight loss is that when you focus on calories, you're, you're losing the [laughs] sort of thread of the energy balance equation. You think that, uh, y- eating fewer calories guarantees you body fat loss. It does not. You can just as easily balance that equation by reducing your energy expenditure.

Dr. Rangan Chatterjee 32:58 Mm-hmm.

Dr. Jason Fung 32:58 Just like if you are working and you get fired, you lower your expenses.

Dr. Rangan Chatterjee 33:05 Yeah.

Dr. Jason Fung 33:05 That's just what you do so that you protect your bank account, right? You don't wanna take money out of your bank, so you lower your expenses. So you reduce your income, you reduce your expenditures. So same thing with calories. You reduce your income, how much you eat, calories in, your body reduces calories out. You don't control that.

Dr. Rangan Chatterjee 33:23 Yeah.

Dr. Jason Fung 33:23 You can't decide to burn more calories, but your body does.

Dr. Rangan Chatterjee 33:28 Yeah.

Dr. Jason Fung 33:28 Now all of a sudden, you're in a situation where you're still overweight, but you're eating 1,500 calories and your body's burning 1,500. So you're cold, you're tired, you're hungry, you feel terrible, but you're not losing any body weight. That is actually precisely [laughs] what has happened, and everybody who's done a diet knows this.

Dr. Rangan Chatterjee 33:48 Yeah.

Dr. Jason Fung 33:49 Every single person. The failure rate of sort of counting calories for weight loss, the failure rate is somewhere around 95 to 99%, and yet we think that this is the scientifically proven way to do things. It's actually proven to fail.

Dr. Rangan Chatterjee 34:05 Yeah.

Dr. Jason Fung 34:05 It's guaranteed. This is practically guaranteed to fail if you don't adjust the foods that you're eating because, as you say, we think it's all about willpower. But really, it's all about eating the right foods because the hormonal response to those foods, which is telling our body to either gain weight or not gain weight, right? That's, that's what tells our body. It's demonstrably different. Like, you eat bread, you eat an egg, we can measure [laughs] the difference in the hormones that-

Dr. Rangan Chatterjee 34:35 Yeah

Dr. Jason Fung 34:35 ... you've stimulated, right? It's not just, uh, airy-fairy. We know it 100% for sure that there is a difference, and yet we have to pretend that those hormonal differences make no... Doesn't matter.

Dr. Rangan Chatterjee 34:48 Yeah.

Dr. Jason Fung 34:48 Right? Which is ridiculous.

Dr. Rangan Chatterjee 34:50 We'll be back to the conversation in just a moment. Now, many of us struggle to find time to eat all of these incredible whole foods. That's why I'm a big fan of good quality whole food supplements like this one that's been in my own life for over three years now. It contains over 75 whole food source ingredients, vitamins, minerals, pre and probiotics, and can help us support our energy, focus, digestion, and our immune system. ATHLETIC GREENS are giving my audience a fantastic offer, one year's free supply of vitamin D and five free travel packs with your first order. You can see all the details at athleticgreens.com/livemore or simply click on the link below. Now, back to the conversation. You know, the other thing I think people miss when they're focusing too much on that equation is that when we talk about calories out, everyone assumes it's just one thing. You know, it's, it's like how much did I exercise, for example, that day. They forget that actually calories out could well be four different things. The basal metabolic rate, as you've mentioned, so, you know, how much energy does it take to keep the lights on in your body, lungs, kidneys, whatever it might be. There's also the thermogenic effects of foods. In the whole context of things it's relatively small, but still that's part of that calories out part of the equation. There's purposeful movement and exercise, which, yes, can burn some calories, although potentially not as much as people think. And then there's also NEAT, you know, non-exercise activated thermogenesis, a kind of non-purposeful movement. All these kind of subtleties people are not thinking about when they're thinking about that equation. So I think for many reasons, while scientifically that equation may be true, in terms of practical application for most people, it has very little value. And I think, I think this is a wider point, Jason, for me, which is there's a lot of technical scientific debate around these kind of topics. Insulin, calories in, calories out. You know, for me, like you as a practicing clinician, it's like, well, you know what? Yeah, we can debate these sort of nuances [laughs] in the science- Or we can simplify things and just help people do what we know and we see repeatedly work.

Dr. Jason Fung 37:10 Yeah.

Dr. Rangan Chatterjee 37:11 Do you know what I mean? And I feel that's one of the, the reasons I, I very much like your approach. You have seen tens of thousands of patients. You've helped probably millions of people through the internet now, and through your books across the world. A lot of people are gaining huge value from this. A- and I think we sometimes miss that when we're trying to dot all the I's and cross the T's with the science. It's important, but it's not everything.

Dr. Jason Fung 37:35 Yeah, absolutely. And, and, and this whole idea that, you know, a certain number of calories, 100 calories of bread versus 100 calories of egg, are going to have different effects on the body. They have different hormonal effects. Um, it boils down practically to a simple idea. That is, some foods are more fattening than other foods. Which is, of course, an idea that your grandmother would have thought blindly obvious, right? [laughs] Like, who gets fat eating broccoli? Like, zero people in the whole world.

Dr. Rangan Chatterjee 38:08 [laughs]

Dr. Jason Fung 38:08 Who gets fat eating cookies? Many, many, many people, right? And she didn't understand the difference between, you know, the hormonal responses of broccoli versus cookies, but she understood that you eat these foods, you know, and this goes back hundreds of years, 'cause the first low carb diet was sort of, like, what, banting in the 1800s, right? So you're talking about at least 150 years people have said, "Hey, certain things really make people gain weight." And even if you go back to Ancel Keys, for example. So he did a very interesting study in the '40s, uh, the Minnesota Starvation Study. Interestingly, it wasn't a s- a starvation study at all. It was a 1,500 calorie a day diet. 1,570 calories, which is actually not far off of what people advise for weight loss. Very high starch foods, because that was what is, was available in post-war Europe at the time. So when he measured metabolic rate, it dropped by, like, 40%. When you drop calories by about 40%, metabolic rate dropped by about 40%. And what happened? He actually measured other things. So heart volume shrank. Stroke volume, like the amount of blood that you pump out, went down. People were cold, so they're generating less body heat because they're burning 40% less calories. Your, sort of, w- these sort of metabolic housekeeping things like how much blood to, you're not pumping blood. You're more tired. You, you get, you know, y- you're, you, you're not generating body heat. You're cold, right? So the whole point is that, yeah, all of these things are important. This calories out is not just exercise. The majority of it is, you know, basal metabolic rate, and you don't control that through your mind, right? You control that through your hormones. It's your hormones that control everything. That's just the way it works-

Dr. Rangan Chatterjee 39:59 Yeah

Dr. Jason Fung 39:59 ... in the human body. Everything is controlled by hormones. You don't control how strong your bones are. That's controlled by growth hormone and other hormones. Parathyroid hormones, right? You don't control how active your thyroid is. So this idea that it's all about willpower, you know. Because people look at this thing and they go, "Body fat equals calories in minus calories out. So therefore, calories in is what you eat, calories out is exercise. It's all willpower." It's like, that's nonsense. It actually doesn't work for anybody. Because you have to actually... It, it is an extremely simplistic way of looking-

Dr. Rangan Chatterjee 40:34 Yeah

Dr. Jason Fung 40:34 ... at things. When you go one level deeper and say, "Okay, so, okay, calories in minus calories out. It's what you eat and what you exercise." Let's go one level deeper. Why is it that you're eating more or eating the wrong foods? Well, it's because you're hungry. So that comes back to your hormones. And then you look at calories out. Well, it's exercise. Let's go one level deeper. It's actually mostly basal metabolic rate. So you can control what you eat, but you can't control how hungry you are. You can't decide to be less hungry. You can't decide that you're gonna burn more calories. So it's all down to your hormones.

Dr. Rangan Chatterjee 41:08 Yeah.

Dr. Jason Fung 41:08 It wasn't due to willpower at all. So you can take a drug such as semaglutide, which is a weight loss drug now. When you completely whack that appetite, you know, in half, people lose weight. It never was willpower. It was that you controlled the hunger as opposed to the calorie, right? It all comes down to hormones. The, the human body is run by hormones. That is, that is the chemical messengers that tell our body what to do. And, and this idea that it's, it comes down to something so simplistic like calories. Calories is such a terrible notion because... Not terrible. It's, it's just misused, because it's the unit from physics, not physiology, right? So it's the amount of heat energy that is contained in a certain amount of food. It doesn't tell anything about how our body's going to use it. A block of wood may have 100 calories. If you eat that block of wood, you will get none of it, right? So it's like, well, you know, that's it, right? I mean, there's-

Dr. Rangan Chatterjee 42:11 Yeah

Dr. Jason Fung 42:11 ... there's, there's lots of calories in a block of wood, but you won't absorb any of it. It's just a unit of physics. Physiology is what happens in the human body, right? Where are the calorie receptors?

Dr. Rangan Chatterjee 42:23 Yeah.

Dr. Jason Fung 42:23 Do we have calorie counters within our body that say, "You took this many calories, therefore this," right? And, and you look at the failure of that sort of academic notion that we can be so precise that we are now physicists, not physicians, right? Like, we're physicians. That sort of stuff from physics doesn't work because it doesn't jive with how the human body works. We don't have calorie counters. We don't have calorie receptors. Like, there is nothing in our body that senses how many calories you eat.

Dr. Rangan Chatterjee 42:54 Yeah. And it doesn't account for the realities of modern life where people are sleep deprived, right? And therefore their hunger and satiety hormones are completely off whack. It doesn't account for chronic stress, which raises that hormone you mentioned earlier, cortisol, which again has a huge effect on our hunger and all kinds of things, and where we might store that body fat. You know, the human body is just much more complex, and I think- I think a lot of people have a certain bias, right? So if you're a personal trainer, I guess, your bias is probably the subset of people you've seen, people who are coming to see you who believe that actually working out regularly, exercising hard is really, really important to lose weight. And of course, it can form part of the overall strategy of things, but therefore your view as a personal trainer is gonna be hugely impacted by what you see. Of course, my view is hugely impacted by what I've seen over 20 years, tens of thousands of patients. But as a general practitioner, I guess one thing I would say is that you see everything. You literally see everything. You see [laughs] , you see people who've got all kinds of issues, and therefore I feel that gives you insight into a whole variety of different people, different lifestyles, people who are shift workers, you know? And you, you know, you're a practicing clinician as well. I guess as a nephrologist you will also see a huge amount of different people, right?

Dr. Jason Fung 44:16 Yeah, exactly, and that's, uh, one of the things that you see a lot of in this sort of fitness world and there's this sort of bro science. Because, you know, you're so invested in this idea that it's all about effort, right? You know, that, that, that all of weight loss is just due to effort and willpower, right? As opposed to, you know, eating the right foods and all these other things that are so important we know, like sleep and stress and so on. Um, I, I used to, you know, and I think we all did of course, we all used to believe that, right? And I always thought in medical school and a- above, I used to think, you know, weight loss is just about willpower. It's about controlling what you eat, right? And I always thought it strange that there are a lot of medical conditions that cause weight gain and weight loss, but weight gain in particular. And I always thought it was strange, because how can a medical condition [laughs] cause weight gain? It's all about willpower. 100% about willpower. It's about calories in, calories out. I, I used... And, and then I thought, how is that possible that you have a medical condition that has nothing to do with willpower, right? So i- if you're, if you have Prader-Willi or any of these other conditions that cause obesity, um, you know, Addison's, uh, sorry, Cushing's disease, um, how can that cause weight gain? Because we know that it's caused by sort of effort, right? [laughs] So it, it's, it's very strange. But as you go on, then you realize, no, it's all about, it's all about the hormones. Like, you give somebody insulin, and I don't really care how much willpower you have, you gain weight. Why? Because you're literally telling your body-

Dr. Rangan Chatterjee 45:59 Yeah

Dr. Jason Fung 45:59 ... to gain that weight. So therefore, if that's the important thing, then how are you going to minimize those instructions to gain weight? Well, you eat natural foods. 'Cause natural foods, even carbohydrate-containing foods, natural ones have far less insulin effect than others.

Dr. Rangan Chatterjee 46:19 Yeah.

Dr. Jason Fung 46:19 And intermittent fasting, when you don't eat, you know, your, your body is going, your insulin levels are gonna go low. Your body's gonna start using calories instead of storing calories-

Dr. Rangan Chatterjee 46:30 Yeah

Dr. Jason Fung 46:30 ... right? So it's all about those, those, those hormonal effects that we have to understand that we said were unimportant because we sort of elevated calories to be the one and only thing. And I think a lot of fitness people and a lot of scientists, uh, in fact, love the sort of simplicity of that idea. But unfortunately, it wasn't really true, and you see it, um-

Dr. Rangan Chatterjee 47:00 Yeah

Dr. Jason Fung 47:00 ... all the time. Like, there's so many people, like doctors for example. There are, there are a lot of doctors who are overweight, and I know a lot of doctors. Most of my friends are doctors, right? And would I say that they have no willpower? Absolutely not. I've seen these people work sort of 36 hours at a time, right? When they put their mind to something, they will absolutely go out and do it. Nothing will stop them. And yet these people are overweight. Some of them are obese. Some of them are my friends. I don't think they have no willpower.

Dr. Rangan Chatterjee 47:34 Yeah.

Dr. Jason Fung 47:35 I don't think they have [laughs] a lack of willpower as the reason that they are overweight. I think they're eating the wrong foods because they... or, or they're getting the wrong advice to eat constantly and so on. And so many doctors have come back to me. So when I started talking about intermittent fasting probably about eight years ago, like honestly, people thought I was insane. Like, it was, you know, common knowledge that you had to eat all the time even to lose weight, right? And when I came out and said, "Well, you can fast," I mean... And, and, and, and most of the doctors that, that I spoke to, you know, the, because they knew me and they would listen to me, they said, "This actually makes a lot of sense." And they were all like, "You know, I remember when I was in residency and training, I'd go, like, 24 hours without eating. Nothing bad ever happened." [laughs]

Dr. Rangan Chatterjee 48:26 Yeah.

Dr. Jason Fung 48:26 "I was so busy in the emergency. I was so busy in the operating room. I had so many patients. I just didn't eat, and nothing really happened other than I was just hungry for a little while, but I was too busy. I ignored it." And I'm thinking, yeah, because when you don't eat, your body is just gonna take whatever calories it needs from your body fat, and that's it. And everybody's like, "Yeah, I was, like, 30 pounds lighter at that time," right? "When I didn't eat constantly."

Dr. Rangan Chatterjee 48:51 Mm-hmm.

Dr. Jason Fung 48:52 So a lot of the, a lot of the physicians would always come back and say, "You know what? This makes a lot of sense from a physiologic standpoint. This idea that you should eat all the time is wrong." So one, you know, fasting is a way to eat fewer calories because you're s- you're taking it from your stores, and you're feeling full because you've taken it from your stores, right? Just like you take food from the fridge, it doesn't mean you're less full. You, you're just as full as if you went to the store. Just you took it, you took those calories from a different place. You took it from storage. Same thing with body fat. You took those calories from storage as opposed to from food.

Dr. Rangan Chatterjee 49:26 Yeah.

Dr. Jason Fung 49:26 No difference in terms of physiology. So yeah, it's interesting because a lot of doctors themselves, even these sort of highly, highly educated people- Would say, and, and, and, and that's the, that's one of the things that, um, you know, I think has, has started to sort of resonate through. Uh, there was an interesting study where they looked at, they did a, they did a Facebook poll of physicians and how they lose weight. Um, and what was interesting was that 75% of people used intermittent fasting in this poll for weight loss, physicians. Yet they only counseled it for about 30%. So the huge gap was that the doctors wanted to lose weight and wanted to do something effective [laughs] which was fasting, but with their patients, they had to give sort of-

Dr. Rangan Chatterjee 50:16 Yeah

Dr. Jason Fung 50:16 ... sanctioned advice, which didn't include the fast.

Dr. Rangan Chatterjee 50:21 I wanna get into some practical information for people. I think one of the really beautiful things you've said so far is that it's not a lack of willpower, and, and, unfortunately, this over-focus on the calorie has led to a lot of people feel really bad, so that they, they think, "You know, I'm really trying. Like I- I'm restricting my calorie intake. I'm, I'm not eating that much, but I can't lose weight." And they feel like failures. They feel guilt. They feel ashamed of themselves, which is really, really toxic to try and make long-term behavior change when you feel like that. So I wanna go into some really practical things. Before we do, just to finish off the calories in, calories out model for a moment, my approach has always been with patients and, and when I, like you, when I write books, I say, "Look, if you find [laughs] that counting calories works for you, and you can fit it into your life and your lifestyle, and you're getting the health outcome you desire, I'm not trying to change your mind. I'm not saying stop doing it. If that works for you, go for your life." I'm just saying in my experience, I haven't found it to be that helpful certainly for, for most people that come to see me. What would you say to someone who is watching this who says, "Jason, listen, um, I actually have no problem counting calories. I like counting them three times a day, and I can maintain my weight, I can maintain my health doing this"? What would you say to that person?

Dr. Jason Fung 51:48 I, I, I agree with you. I mean, if something's working for you, then go ahead and do it. Like there's no reason to stop. And, um, you know, it, it really goes for any- anything. It's, it's, it's, uh, if you're eating 10 times a day and you're doing well with it, then go ahead. Like be my guest. And we know every- everybody reacts differently, so I'm okay with that. But if, if you wanna make a change, then, you know, you could probably go to, that's where to start, right? Here's a good place to start, and then you decide what to do with it. And I think the other thing, you know, I think you said that was very good was that this idea of, um, sort of people who aren't losing weight, what happens, of course, is that when you focus on calories and say, "It's all about willpower," what you're saying to these people is that they don't have the willpower, which I think is absolutely not true. Because it's, it's one of these embedded assumptions in the calories in, calories out model that is, that nobody acknowledges, which is that calories out can go down. Your ba- basal metabolic rate can go down when you diet. So therefore, if you are not losing weight, even as you lo- as you eat fewer calories, you could still not lose weight because your metabolic rate is going down along with it. So why are you blaming these people? And that's, that's where you get a lot of, um, you know, a lot of people sort of just have made that assumption that calories out is going to stay stable at 2,000 calories a day, right? This is the whole thing when you read these people who are like, "Oh, just, just cut 500 calories a day. You'll lose a pound a week." That actually never happens because that assumes that your calories out, your metabolic rate stays at 2,000 calories.

Dr. Rangan Chatterjee 53:40 Yeah.

Dr. Jason Fung 53:40 Every physiologic study we've ever done says it goes down. A- and you know it must go down. So for example, if you take somebody who's, uh, 200 pounds, you say, "Cut 500 calories a, um, you know, a day. You'll lose a pound a week," does that mean in 200 da- uh, weeks they'll lose, they'll weigh zero pounds? Like no, absolutely not. That will never happen even if you stick to 1,500 calories. So therefore, your metabolic rate must go down at some point. Turns out it goes down almost immediately and persists. So therefore, this idea that it was all because they skipped on their diet, right? That, that's not true. It might have just been a very poorly constructed diet-

Dr. Rangan Chatterjee 54:22 Yeah

Dr. Jason Fung 54:22 ... that is not taking into account just the foods, but also the sort of eating duration, the fasting, the hormones, what hormones you're stimulating with the foods that you're eating, what information you're giving your body, what instructions you're giving your body. There's so much of that other, other things that are important.

Dr. Rangan Chatterjee 54:41 Yeah.

Dr. Jason Fung 54:42 Um, yeah, and, and I think it's time to take that, that, that sort of, uh, guilt and shame away from those people. We're all sort of working together.

Dr. Rangan Chatterjee 54:51 Yeah, it's, it's a great point.

Dr. Rangan Chatterjee 54:52 Let's get to, um, the sort of practicalities. You've mentioned in your books, you mentioned in this conversation that chronically elevated insulin is problematic for a whole variety of different reasons. Yes, for the developments of type 2 diabetes, of putting on weight. Also, you know, a lot of people aren't aware that it increases blood pressure, increases fluid retention, increases, uh, a type of cholesterol called VLDL, very low density lipoprotein, which can be problematic. And so for a variety of reasons, we wanna lower that. So there's two broad ways I'm getting that we can do that. One is through a diet that does not constantly push up insulin, and the other way is with a form of intermittent fasting Or, you know, bringing in some type. So if we, if we start off with food and diet, you mentioned low carb early on in this conversation. Of course, we know how divisive, um, the diet landscape currently is. In your experience, if we're thinking about a diet, food choices that don't spike insulin too much, what are the kind of principles you like your patients to follow?

Dr. Jason Fung 56:07 Yeah, and I think this is where, um, you know, there's always a lot of difference in opinion, there's low carb versus high carb. And I actually think that there's a huge difference even within carbohydrates. So the, the problem is not generally the carbohydrates, but the processing that makes the biggest difference. So if you look at the glycemic index, which is, um, you know, which looks at carbohydrate-containing foods, sees how much insulin tends to go up and glucose tends to go up, they tend to go up together, uh, of certain foods, what you see is that unprocessed carbohydrates tend to cause a lot lower spike in insulin than, than processed foods. So you take cereals like Cheerios and stuff, they're really, really high. You take a very refined product like white bread, uh, just very, very high. But then you look at something like boiled potatoes, and it's just extremely low. They're both carbohydrate-containing foods. Um, so there, there's a big difference even within carbohydrates. Beans, beans are carbohydrates. They have a different type of amylopectin. They have amylopectin C versus amylopectin A. Their digestion is completely different. They're still carbs. So trying to simplify it to just carbs is difficult, because you could eat a lot of beans, and who gets fat eating beans? Like, very few people. Um-

Dr. Rangan Chatterjee 57:35 Are you talking like black beans, kidney beans, these sort of things?

Dr. Jason Fung 57:38 Yeah, all beans.

Dr. Rangan Chatterjee 57:39 Yeah.

Dr. Jason Fung 57:39 Yeah.

Dr. Jason Fung 57:39 The type of carbohydrate they contain is amylopectin C, which is harder to digest and therefore leads to much lower blood glucose levels, much lower insulin levels. Um, but insulin is sort of that key. So even within carbohydrates, so, so people think, well, one of the things is to cut carbs, which is, which is a reasonable thing, but cutting the refined carbs does a lot better. 'Cause you have to understand that a lot of countries, a lot of cultures have had high carbohydrate intakes, and in the past have never had a big problem. So China, for example, was classic in the '80s. It was eating 300 grams a day of carbohydrates, almost all white rice, and there was almost no obesity. This is 1980. Then, of course, recently they, they, they started eating a lot more processed foods, a lot more sugary foods. Now their obesity is just exploding. But it was not just the carbs.

Dr. Rangan Chatterjee 58:31 Why do you... This is really interesting for me. So white rice is a refined carbohydrate. Why do we have societies with high volumes of carbohydrates who are not putting on weights and who are not getting type 2 diabetes? And that example you used of China there is really interesting. 300 grams of white rice a day, you would think would spike insulin [laughs] and would, um, you know, cause people to get sick, but it wasn't.

Dr. Jason Fung 59:00 No, it wasn't.

Dr. Rangan Chatterjee 59:01 And, and what if... You know, one of the theories I put forward in my first book was this idea that maybe in the West, in the m- the modern world in which we now live, where people are chronically stressed, they're chronically underslept, they're chronically underactive, and they're eating a lot of highly processed foods, all together, that's creating the perfect conditions for high levels of insulin resistance. And I thought, well, maybe the low-carb diet has a particular utility in modern, stressed-out cultures. I, I don't know, have you got any comments on that? And how do you explain that in the 1970s they were eating this in China and not getting sick?

Dr. Jason Fung 59:40 I think there's a few things. One is that the amount of sugar they were eating was just almost zero.

Dr. Rangan Chatterjee 59:46 Yeah.

Dr. Jason Fung 59:47 So sugar, which is fructose, is metabolized quite differently than glucose. So when you metabolize glucose, all your cells in the body can use glucose. When you metabolize fructose, only the liver can use fructose. So the fructose goes straight to your liver, and there it gets converted and causes fatty liver, it causes all kinds of things when you're eating too much fructose. Um, so it can get converted back into glucose, but for a lot of reasons, it just gets turned into fat through de novo lipogenesis. You get fatty liver, you get insulin resistance, which causes hyperinsulinemia. So the fructose is actually much worse for you than the glucose, in my opinion, because, you know, if you are 150 pounds, you have 150 pounds of body that's using glucose versus sort of five pounds of liver that can metabolize fructose. So the fructose is much, much more, uh, obesogenic, I think, than the, uh, glucose. So therefore, the practical side is that sugar and sweet things like that are just much more fattening than starchy foods.

Dr. Rangan Chatterjee 1:00:54 So maybe you're saying then in China back then, because they're not having much fructose-

Dr. Jason Fung 1:00:59 Yeah, almost zero

Dr. Rangan Chatterjee 1:01:00 ... th- therefore they can actually, the bodies can handle the 300 grams of white rice each day. Whereas on the background of a lot of fructose, which, which is of course how many of us live these days, too much sugar, too much fruit juice, all these kind of things, maybe with a background of that, suddenly the white rice starts to become problematic?

Dr. Jason Fung 1:01:21 Uh, yeah, I think so. I think the fructose, uh, really makes that, that much worse. But the other thing is, um, that there's different reasons why... A- and two, they weren't eating all the time, right?

Dr. Rangan Chatterjee 1:01:33 Yeah.

Dr. Jason Fung 1:01:33 They weren't eating constantly. It's not like they're eating eight times a day of white rice. And the third thing I think that's sort of always overlooked, because it doesn't fit into this neat little square, is that there's different reasons why we eat. Like, there's the hunger, the nutrition part of things, which we think is important, but in this day and age is probably the least important of the reasons that we eat. There's the habits, right? You eat because it's time to eat. That's really the only reason, and you eat because it's delicious. So if you take any diet that is monotonous, so no matter what diet it is, so you could eat, say, say you love pizza, but I give you pizza breakfast, lunch, and dinner. Okay, very soon, [laughs] much sooner than you think, you are going to be so sick of pizza that if I continue to feed you pizza, you're just gonna say, "Okay, I'm gonna eat as little of this pizza as I possibly can until I'm no longer hungry because I just don't like to eat it." It's the same thing with white rice. If you eat white rice and vegetables every single day, three meals a day, which is, you know, what they're eating in China, like different types of, you know, vegetables with white rice, pretty soon you're gonna be like, "I will eat the rice because I'm hungry. As soon as I stop being hungry, I am stopping eating," 'cause I know w- I, I... the, the hedonic effect of food, the pleasure-giving sense of food goes away when it's, it's completely monotonous. So you can eat all that, and, you know, you're not gonna overeat it because you don't want to.

Dr. Rangan Chatterjee 1:03:16 Yeah.

Dr. Jason Fung 1:03:16 You just wanna make sure you're not hungry, and therefore, any monotonous diet always works because you've just very quickly run out of things that you want to eat.

Dr. Rangan Chatterjee 1:03:27 Yeah.

Dr. Jason Fung 1:03:28 So what we've done, of course, in the modern age is we've introduced all kinds of varieties of food which keeps us eating beyond the we're full sort of stage. I've got my nutrition. I'm done. I don't wanna eat anymore. We never get that state because we're always like, well, you know, we wanna keep eating, and then you get around it by snacking because even if you... there's lots of good things to eat. So you go to a buffet, you know, all-you-can-eat restaurant. You know, after a certain point, you have to stop. Like, you can't keep going. It's, you know, if you've eaten everything and somebody says, "Hey, why don't you have a bit more of this pork chop?" You'd be like, "Ugh, that's gonna make me throw up," right? It's the same pork chop as you ate like 20 minutes ago, but you're now full. So the, the point is that if y- if you take away the sort of pleasure-giving part of food, then you're gonna be able to control a lot of overweight-

Dr. Rangan Chatterjee 1:04:28 Yeah

Dr. Jason Fung 1:04:28 ... obesity, which is what the white rice was, right? It was monotonous. It was just every single day was the same thing. Like I, I can tell you, I, I, I, I ate rice a lot growing up because my, my parents were immigrants. They came from, from, uh, Hong Kong. We ra- ate rice probably every single day. So yeah, I liked rice a- a- all right, but, you know, until you're full, then that's it. Like-

Dr. Rangan Chatterjee 1:04:52 Yeah

Dr. Jason Fung 1:04:52 ... you know, I, I don't wanna eat more than I [laughs] have to because I've eaten too much of it a- a- already. So, so that's why it's always, you know, people say, "Oh, therefore carbs are good," or you have the Kempner rice diet from the '40s. "Hey, that proves that carbs aren't the enemy." It's like, no, no, no. It's very complicated. Like you, you can't just simplify things into-

Dr. Rangan Chatterjee 1:05:14 Yeah

Dr. Jason Fung 1:05:14 ... like this food is good, and this food is bad, right? So it... th- there's a lot that goes into sort of understanding-

Dr. Rangan Chatterjee 1:05:22 Yeah

Dr. Jason Fung 1:05:22 ... it, and satiety plays a big role in that. That is why the things that are most successful at controlling weight are hormonal agents that control your appetite, so nicotine is a classic example that it actually suppresses your appetite. People notice this when they stop smoking, that their appetite goes up, and it's probably 'cause it, it was chronically suppressed. Same thing with semaglutide, the drugs that, some of the drugs that are used now. But anyway, so, so it means that the carbohydrates are not the only thing that matters.

Dr. Rangan Chatterjee 1:05:52 Yeah.

Dr. Jason Fung 1:05:52 It matters, um, the type of carbohydrate, so is it amylopeptin A, amylopeptin C, how often you're eating it because it's not just how high you spike it, and, and how refined it is gonna affect how high it spikes. The foods you eat it with are also going to make a difference, and this is always very interesting to me because you can take the same foods, and you're... That's not what's important. The hormonal response is what's important. If you take the same food at breakfast versus dinner, you're gonna have a different insulin response to it.

Dr. Rangan Chatterjee 1:06:26 Yeah.

Dr. Jason Fung 1:06:26 So you're gonna actually have a much higher insulin response at nighttime versus breakfast. Same thing with something like vinegar, uh, and this is very interesting actually, I think. So when you take sushi rice, for example, which is vinegared rice, um, when you take an acid or lemon juice with bread or vinegar with bread, for example, you can take, uh, say 100 grams of bread, and you can measure how much your glycemic index goes up, and when you take it with the acid, it's like 50%, 60% of what it was without the acid, which is fascinating because it's the same 100 grams of carbohydrate. So say you take white rice versus vinegared rice. The glucose level and the insulin level goes up to about 65, 69, something like that, versus 100, so you have much less effect. And there's an interesting reason why that is, and it's because there's, in terms of digestion of starch, it's digested by a hormone called amylase. There's salivary amylase, and there's pancreatic amylase. So the assumption, so you eat bread. The saliva contains amylase, starts breaking down that starch because remember, starch is a chain of glucose. You need to break it into little pieces so that you can absorb it. The sa- saliva contains amylase that immediately starts to work it, and we had assumed always that most of the digestion is through the pancreas. It turns out that up to 80%, 60 to 80% of the digesting can be salivary amylase, because salivary amylase is deactivated by low stomach pH. So we assumed you chew it, boom, it goes into the stomach, and all of a sudden salivary amylase stops. It stops breaking down the starch. But in fact, because of the bolus of food, the pH of the stomach actually never gets down there, and that doesn't get low enough to deactivate salivary amylase. So if you take something like bread with vinegar, like they do, you know, olive oil and vinegar, for example, turns out that y- your, you d- don't break down the same amount of starch, and therefore your glycemic index goes, uh, much lower, your insulin spikes go much lower, and it's because of the acid in the food.

Dr. Rangan Chatterjee 1:08:44 Yeah.

Dr. Jason Fung 1:08:44 Lemon juice does that. Fermented food does that, which is lactic acid. Uh, vinegar, which is acetic acid, does that. So there are things that you can take with the carbs that will also affect it. If you take carbs first versus last in the meal-

Dr. Rangan Chatterjee 1:08:57 Yeah

Dr. Jason Fung 1:08:57 ... you take it with protein or with fat, it's gonna make a difference, and there's so many things that make a difference-

Dr. Rangan Chatterjee 1:09:01 Yeah

Dr. Jason Fung 1:09:01 ... other than just cutting the total number.

Dr. Rangan Chatterjee 1:09:03 Yeah, I love that, and, and I think that officially qualifies as a hack. You know, [laughs] the term hack is, you know, thrown around a lot these days, but that seems like a really practical thing that people can do within the context of their own diet just to lower that glucose and lower that insulin response in the body. The other thing, of course, they can do is think about the food order, and I know you released a video recently on your YouTube channel about this. Why is the order in which we eat foods important when we're thinking about glucose and insulin?

Dr. Jason Fung 1:09:33 Yeah, and it's, a- again, it was the same sort of thing where they did a study where they had people, they ate carbs first and then waited 10 minutes, then had their fat and protein, versus taking the fat and protein, then waiting 10 minutes and then eating the carbs. And again, same number of carbs, same type of carbs, right? Same food, same amount of food in the carbs exactly, yet the rise in the insulin was, like, 50% of what it was. And remember, the insulin is what's telling your body to, "Hey, store this, this energy, store these calories away." So the less of this insulin you have trying to, to store it away, the more you're gonna leave out in the body for you to use as energy, and it's gonna keep you fuller longer. So that's, that's the, the food order. So basically the, the whole hack would be just shift your carbohydrate intake to the last part of the meal instead of the first part of the meal. And that's gonna do two things. One, it's gonna make you less wanting to eat the carbs, 'cause you're already full from the fat and protein.

Dr. Rangan Chatterjee 1:10:34 Yeah.

Dr. Jason Fung 1:10:35 And two, the amount of carbs that you take, even if it's the same, is gonna have less of an effect on you. So it's, it's, it's... So, so, you know, this is what I mean when I say it's a complicated topic, and people who try and simplify it to total calories or total carbs always wind up missing a few things, because there are ways to get around it, because, you know, w- we, we, we have eaten carbs in the past without, without gross-

Dr. Rangan Chatterjee 1:11:00 Yeah

Dr. Jason Fung 1:11:00 ... you know, worldwide obesity epidemics, right?

Dr. Rangan Chatterjee 1:11:03 Yeah. This is something I've, I've done for a good couple of years now, and more recently with the kids. [laughs] My kids are 12 and nine at the moment, and I will, if, if I'm cooking dinner, I will serve them their protein source and their vegetables first [laughs] , and when that's finished or almost finished, then I'll put on, I don't know, the sweet potato mash or whatever else, you know, whatever whole food carb we're serving with it. And, you know, because it's very hard for me as a parent n- [laughs] knowing the science and knowing the impact not to try and implement it, because it's pretty straightforward to do, actually, and it's something that I think anyone listening to this or watching this right now can, can experiment with themselves. You know, eat the carbs last. And, you know, there's a, there's a really good video on your YouTube channel that I think will help people understand the science of that as well. Um,

Dr. Rangan Chatterjee 1:11:53 Jason, moving to fasting, intermittent fasting, right? If someone's kind of heard what you've had to say so far and is thinking, "Okay, all right, um, I'm interested in trying intermittent fasting," where would you encourage them to start? And, and before you answer, I also wanna say one of the things I think is so great about the practice of intermittent fasting is that it doesn't really matter what dietary tribe you belong to, you can still practice this and get benefits, right? So I think it cuts through straight away through all that noise. Um, so yeah, maybe, maybe some tips for people on, on where they might want to start.

Dr. Jason Fung 1:12:36 Yeah, I think that the, the first place to start really is just to go back to sort of, uh, you know, eight hours, 10 hours of eating sort of thing. Um, eat i- i- if you wanna eat sort of breakfast at 8, 9 o'clock in the morning and finish by, like, 6 o'clock in the evening, and then let the rest of the time be fasting. You know, you're talking about a eight, nine, 10-hour eating window. It may be 14 to 16 hours, and tha- and that's relatively easy to do. And of course, it's something that people have done for, for many, many, uh, years. So cutting out the snacks, cutting out the late-night eating, and then, you know, so if you cut out the eating after dinner and push your breakfast a little bit later, then, then you're automatically gonna get that, that period of time, and that's a great place to start. And then you can experiment. You can go longer or fa- uh, or shorter, depending on what you like. Um, but I think that's, that's probably a good place to start off with. That's gonna be safe for everybody. Um, you know, there's no, there's no problems with, with anything. You're still gonna be eating a relatively normal, um, you know, meal schedule and so on. But, you know, there's so many di- Or there used to be at least. So many sort of, uh, myths about fasting, about how it was so damaging to you and all this. I, I think, you know, it's important to get that right information as well. People used to think, "Oh, well, you know, it's, it's gonna burn muscle." And it's like you hear this all the time. And I'm always like, okay, if you're an elite athlete, sure, maybe, maybe that's something you have to be mindful of. But for most people who are not elite athletes, um, you're just sort of regular, uh, people, you know, this idea that it's gonna burn muscle is still very much ingrained. You see it out there. Lots of people talk about it. And it's like, do you really think that our body is just so stupid that we would store calories as glucose and body fat, but the minute that you don't eat anything you're gonna burn muscle? Like, do you think that we survived as a species to become the dominant species on Earth because our body is so intrinsically stupid? Like, it's sort of like storing firewood, you know, for the winter, and then as soon as it gets a little cold, you chop up your sofa and throw it in the fire.

Dr. Rangan Chatterjee 1:14:59 [laughs]

Dr. Jason Fung 1:14:59 Like, what? Like, what? Like, why are you storing body fat if you plan to use that, that, that muscle? It's, like, ridiculous. And I think it, it's a, it's a huge misunderstanding of the physiology. So I have a video about the five stages of fasting, and there's a period of time in there that actually is called gluconeogenesis. So when you think about the physiology of fasting, there's a lot of good things that happen. But essentially, your body goes from eating food, then it starts using glycogen, which is sugar. It's, it's basically chains of glucose that are stored in your liver. And then after glycogen, then there's a short period of gluconeogenesis, which is protein, and that's where people say, "Wow, that's your, that's where you're breaking down muscle." And you kind of have to say, "No, protein is not the same as muscle." Protein is a lot of things. There's lots of excess protein in our bodies. Skin, for example, is protein. Connective tissue, the thing that binds it all together, is protein. When you break down proteins, your body's gonna break it down and then rebuild whatever it is that you need. So if you need muscle, you will build it. If you don't need it, it won't build it. Like, the only thing that builds muscle... What, what builds muscle and loses muscle is not how much or how little you eat or protein you eat, it's the exercise that you do. Like, I'd love it if I could eat and build muscle, but I don't. [laughs] Like, it doesn't happen ever, as much as I want it to. And it's the same thing. When you're breaking down protein, it's not necessarily muscle. If you're using the muscle, it's not gonna get broken down. But what you are gonna do is break down the skin, the connective tissue, the stuff that you don't need, and this is this process called autophagy where your body's actually going to break down organelles in the body because it's not necessary. And it's a process of cleaning out the unnecessary stuff. So people who did intermittent fasting, we have people lose, you know, 100, 150 pounds. We haven't sent anybody for, um, skin removal surgery, because that was protein that was removed, not fat. And that's all anecdotal, I know. It's not sort of proof. But we have a lot of people who say, "Wow, my skin has tightened up too." It's like, you don't get that with just body fat loss. That's protein loss.

Dr. Rangan Chatterjee 1:17:14 Sorry to interrupt. If you are enjoying this content, there's loads more just like it on my channel. So please do take a moment to press Subscribe, hit the notification bell, and now back to the conversation.

Dr. Jason Fung 1:17:26 If you, if you look at the amount of protein on the human body, in somebody who's overweight, it's, it's far in excess. They have more protein than somebody who's, who weighs less. It's not just the fat. It's all the stuff that helps to support the fat. The, the blood vessels, the skin, the connective tissue, right? And that all also has to go-

Dr. Rangan Chatterjee 1:17:46 Yeah

Dr. Jason Fung 1:17:46 ... with that. So, yes, there is a period of breaking down proteins during the period of fasting, sort of around 18 to 24 to 30 hours, something like that. But it's not necessarily a bad thing. It doesn't mean your body is breaking down muscle.

Dr. Rangan Chatterjee 1:18:01 Yeah.

Dr. Jason Fung 1:18:01 You will lose muscle when you don't use muscle.

Dr. Rangan Chatterjee 1:18:04 So you're saying start off for people maybe a 10-hour eating window, as you say. M- let's say 8:00 AM till 6:00 PM is your eating window. Out with that, what, in your view, 'cause you take a lot of people through these fasting programs, I know, in your clinic, what are they permitted to do outside that eating window in terms of drinks, uh, and other things? That's the first question. And then going beyond that, it's like what benefits then might people, once they start there and go, "Okay, this is pretty easy. I can do that. I'm feeling better. Lost a bit of weight. I'm sleeping better. I feel lighter," what are the benefits or why should some people consider going further? 'Cause I think in your clinic d- am I right in saying that sometimes you take people into 36-hour fasts, 48-hour fasts, those sort of things? So maybe just, yeah, just, just, just walk us through that if you, if you will.

Dr. Jason Fung 1:18:59 Yeah. So, you know, a classic fast is water only. But really you don't have to be that strict. There's no rules. Like, uh, you know, when you're talking about fasting, there's two main variables. One is the length of fast, and two is what is allowed during that fast. And you can put... Y- there's lots of things. So tea, for example, is something that I recommend for a lot of people. Um, you can drink coffee. And then those really don't have too much effect on, you know, your body. There's no calories in, you know, green tea, and, uh, it really doesn't have much effect. On the other hand, the coffee and stuff, it's gonna have... The coffee and tea, they both have things like stimulants, like caffeine, and that may keep your sort of energy, uh, you know, your, your metabolic rate a little bit higher. So yeah, maybe there's a little benefit from those, although the effect is relatively small. So teas, coffees, herbal teas, those are all great to do. Then you get into things that are more clearly food, uh, so things like bone broth, for example. And then people even take, like, small salads and stuff within that fasting window, you know, if they get very hungry, for example. And those are, you know, people think, "Well, you know, I just broke my fast," right? "I have to start all over." That's not what happens. Because what happens is that when you're fasting, you're trying to force that insulin level down. So if your insulin level's going down, your body's going to switch towards using your, your, your stored calories, not, not the food. If you break that fast with, say, you know, oh, I had, you know, um, some bone broth, yeah, your insulin's gonna blip up for a little bit, but it's a very small amount, and then it's just gonna start going back down again. It's not gonna have a huge effect. So even if you take something during that fasting window, it doesn't mean that all of your progress has been lost and you have to start from scratch again. So y- you don't have to worry so much. But generally, I tend to tell people, you know, just stick with, like, teas, coffee. If you put a little bit of cream in the coffee because that's what you're used to, go ahead. It's not gonna make a huge difference. But don't put, like, the whole, you know, carton of cream in it. Then, then you're talking about food more than anything else. And then the other thing is in terms of the benefits of fasting, why continue with it? Um, there's a lot of reasons. Like, if you think about the physiology of what happens during fasting, there's a lot of good things that happen. People always assume that they're gonna be tired, uh, during fasting, but that's not actually what happens. So i- if you, if you, if you don't eat, there's a very sort of stereotyped response. That is, insulin's gonna go down, but certain other hormones are gonna go up, and one of those hormones is the sympathetic nervous system and growth hormone. So both of those go up as you fast. Sympathetic nervous system is part of this, uh, sort of, uh, parasympathetic is sort of relaxing. Sympathetic is sort of stimulating. It's a sort of fight or flight response. So it's, it's, it's, uh, the hormones involved are mostly noradrenaline and adrenaline. So you actually activate the sympathetic nervous system when you don't eat, and this is sort of basic first-year medical school stuff. It's ex- it's, it's a number of hormones called the counterregulatory hormones. You get a spike of this counterregulatory hormone in the morning, um, around 5:00 AM, 4:00 AM, 5:00 AM, and it sets you up for the day. It's pushing the sh- the, the, the, the, the calories, the energy b- into the system so that you have energy for the day ahead. So that's why you don't necessarily have to eat the minute that you get up because your body's already started fueling yourself from its stores. And because you're having higher levels of sympathetic nervous system, you're gonna be able to concentrate better. You're gonna have more energy as you fast, not less energy. Like, think about it, uh, you know, if you have a, a lion who just ate. It's sort of sleepy, just wants to lie there and digest. But you have a hungry wolf. Is it sort of, like, falling over because it can't concentrate? No. The hunger is what makes it dangerous because it's dialed in. It's concentrated, and it's got energy to burn. It's just getting its energy from its stores, not from its food, and that's because that you've ... And it, it, you know, again, it's not some voodoo magic [laughs] psychology. It's just physiology. Your body is ramping up at the time that you're fasting.

Dr. Rangan Chatterjee 1:23:23 Yeah.

Dr. Jason Fung 1:23:23 Well, that's great. You're gonna have more energy. I've had people come in, you know, women and, and their husbands would be like, "I can't keep up with her anymore, like, she walks so fast. I can't even ... I, I have to tell her to slow down." And so she's like, "And, you know, it's because I have so much energy." It's like, yeah, because now you're releasing that energy.

Dr. Rangan Chatterjee 1:23:42 Yeah.

Dr. Jason Fung 1:23:42 You've now finally allowed your body to access the stores of energy. By allowing insulin to fall by fasting, you're allowing your body to s- access this huge store of calories, this [laughs] 100,000 calories that you've had stored away, that you've never been able to access before because insulin is always blocking you.

Dr. Rangan Chatterjee 1:24:01 Yeah.

Dr. Jason Fung 1:24:01 Now you have access to this energy. They're like, "Whoa, okay, let's use it. Let's use it." Your body's pumping up the, the sympathetic tone. Some people actually can't sleep because, because they're so pumped up when they're fasting. But then they can focus better. We know that people, you know, in terms of their mental abilities are, do better with fasting. So it's, it's a-

Dr. Rangan Chatterjee 1:24:20 Yeah

Dr. Jason Fung 1:24:20 ... fascinating, uh, process, but a lot of good stuff there.

Dr. Rangan Chatterjee 1:24:24 It's, it's just crazy how many people have never, ever experienced anything like that because of what we were talking about right at the start of this conversation, where, you know, the 50% of the US population who don't work in shifts are consuming foods over 15 hours a day. So they're nowhere near able to actually experience these things that you're talking about. And I think another thing which I often think about with fasting is that humans have been fasting [laughs] for donkey's years, right? If it was dangerous, how would we possibly have survived this far? Now, on that, I think a couple of caveats, and I know you deal with a lot of patients with Type 2 diabetes. Do people, in your opinion, need to be careful if they are taking blood sugar-lowering medications or injecting insulin? I think we should just sort of briefly mention that in case people jump straight in.

Dr. Jason Fung 1:25:20 Yeah, absolutely. So remember that when you're, um, fasting and your body's gonna be using glucose, stored glucose, whether it's in your blood or whether it's in your liver, uh, if you're taking medication in addition to lower your blood glucose, you could possibly go too low. And yes, it can be very, very dangerous. So you, if you're on medications, you should always speak to your doctor. But for a long time, people used to say, "Well, that's why Type 2 diabetics can't fast." It's like, [sighs] no, that's why you have to be careful because the thing about the fasting is that it is a way to help lower your blood glucose. If you're lowering it with fasting and you're taking your medication, then you'll go too low. But it doesn't mean that you should not fast.

Dr. Rangan Chatterjee 1:26:02 Yeah.

Dr. Jason Fung 1:26:02 It means you need to take less medication. It means y- you're overmedicated. So you need to adjust that medication.

Dr. Rangan Chatterjee 1:26:08 Yeah.

Dr. Jason Fung 1:26:08 Not that the fasting was wrong. Because the- You know, this is a natural way to lower your blood glucose. Like, what could be better than that? You're gonna-

Dr. Rangan Chatterjee 1:26:19 Yeah, but we, we, we don't see that as doctors, do we? You know, it's like-

Dr. Jason Fung 1:26:22 [laughs]

Dr. Rangan Chatterjee 1:26:22 ... no, it's, it's a g- given that you stay on the medication. Oh, no, this is dangerous, so adding in fasting. It's like, well, hold on a minute. It's just you can think of it as a third medication, and just think, oh, if I'm gonna add this one in, maybe I need to take this one down or take this one off. But it- it's not... It, it speaks to this wider problem that we don't, as a profession, in my view, give things like fasting or changes in food quality the same priority, the same level of importance as, you know, tinkering this medication by 10 milligrams here. Do you know what I mean? It's kinda like, no.

Dr. Jason Fung 1:26:56 No, absolutely.

Dr. Rangan Chatterjee 1:26:57 It, and it's, it's very frustrating.

Dr. Jason Fung 1:26:59 It is, because, um, for example, you'll have, um, if somebody is on insulin, for example, and their blood glucose goes down. So what is the advice that we as a profession give? Well, eat something, right? It's like, okay. Well, sure. At that one specific time, yes, I agree. But in general, if you're going down, it means you're overmedicated, because I'm giving you this insulin to get your sugars low, and your sugars are going too low. So you're overmedicated. So you need to reduce the dose. But we don't think that way, because we think, okay, well, what you should do, and this is... I, I've heard actually dieticians say this all the time. You need to eat to cover your insulin. And it's like, what? [laughs] So if you take insulin, your sugars go low, then you eat. What do you think is gonna happen? You're gonna gain weight. If you gain weight, what happens to your type 2 diabetes? It gets worse. Why don't you instead not eat, take less insulin, and then you're gonna lose weight? As you lose weight, your type 2 diabetes will get better. But you're absolutely right. Like, we've gone in the wrong direction, thinking that the, the medications are what's good for us, and everything else has to fit around that. And it's, it's part of the problem is medical education, because, a- again, I've gone to so many meetings, and these are given by the heads of, you know, diabetes associations and stuff, right? And they'll go, "Okay. The number one, two, and three, uh, treatments for type 2 diabetes is, you know, diet, diet, diet." Right. Okay, great. Then they spend the next 59 minutes out of that 60-minute lecture telling you about drugs. So the message to all the doctors, these are training doctors and established doctors, is that, yes, we will give you lip service about diet and lifestyle, but what we're really here to talk about-

Dr. Rangan Chatterjee 1:28:48 Yeah

Dr. Jason Fung 1:28:48 ... is meds, right? And that's wrong.

Dr. Rangan Chatterjee 1:28:51 Yeah.

Dr. Jason Fung 1:28:51 That's absolutely wrong thing, because-

Dr. Rangan Chatterjee 1:28:54 Yeah

Dr. Jason Fung 1:28:54 ... think about this simplistically, right? [laughs] Type 2 diabetes is largely a dietary disease, and we're using drugs to control a dietary disease, while you're not going to get as much effect as you think you will, because you're not focused on the root cause, which is the diet.

Dr. Rangan Chatterjee 1:29:12 Yeah. Uh, this is such an important point. When, when I teach doctors on this prescribing lifestyle medicine course, a lot of doctors will say initially that, "Oh, patients don't do what I tell them to do," you know? And I often give the example of a 10-minute or a 15-minute consultation with a patient in general practice where they've just been diagnosed with type 2 diabetes, and we do a role play on stage. I basically try and demonstrate two different consultations, one where basically you spend the first 9 of those 10 minutes or 14 out of those 15 minutes talking about medication and the fact that this will stabilize your blood sugar. You're probably gonna need another medication in the next year, and within a few years you're gonna be on insulin. And then as they're walking out, you say, "Oh, and if you could lose a bit of weight and move a bit more, it's gonna help you." And then we do another one where actually you spend the first 90% of that consultation helping them understand what's caused it, giving them help as to how they might change their lifestyle, all these kind of things. And then you also mention that there may be some medications. And you, you ask the question, so the doctor says, "Well, what message is that patient gonna get?" If you spend 90% of the time on lifestyle and 10% on medication versus the opposite, what's going to happen? Of course the patient's gonna go out with the impression, yeah, he mentioned diet at the end, but really it was all about these medications. But it is starting to change. That, that is for sure. Maybe not fast enough for people. You mentioned women before, and a woman who was full of energy, and her husband wasn't able to keep up.

Dr. Rangan Chatterjee 1:30:42 There's another kind of maybe a myth about fasting, which is that it suits men better than women. Have you heard that myth, and what has your experience been with that?

Dr. Jason Fung 1:30:52 Yeah, I've heard this myth before, that women shouldn't fast or they can't fast or they don't get results from fasting, and it's really, I think, just not true. Like, not all men do well. Like, [laughs] there's lots of men who don't do well. You just don't hear about them. Um, the women can fast. Like, there's nothing inherently dangerous about fasting in women. They do probably respond a little bit differently. Like, men tend to- some men lose a lot of weight, like, right up front.

Dr. Rangan Chatterjee 1:31:24 Yeah.

Dr. Jason Fung 1:31:24 Like, very, very quickly. Like, you know, sort of like 60 pounds in, like, you know, a month sort of thing. Like, really, really fast. And, uh, where- whereas women, uh, do tend to be sort of, like, more slower and stable, and I think some of it is just the sort of baseline. Like, some men really just ha- like, their diets are just really, like, they're obviously not good. Like, they're just eating out fast food, like 100% [laughs] of their meals sort of thing, right? So it's just such a horrific baseline, uh, of processed food that as soon as you change that, like... And, and, and you don't see that with women. Women are t- tend to be a lot more diet conscious. Um, so then you don't get people who have those horrific baselines of McDonald's for every meal sort of thing. Whereas you do that, you do see that with men. Like, with men, you, you get that. And therefore, you know, as soon as you change them to sort of, like, whole foods- ... th- their, their weight just undergoes these dramatic changes. So I think that it's, you know, not just the fasting-

Dr. Rangan Chatterjee 1:32:32 Yeah

Dr. Jason Fung 1:32:32 ... but it's the foods as well, right? So there's two components, right? There's the foods that you eat, and then there's the time that you're not eating. And I think it's, it's, yes, there, there probably are some differences with men and women, like people talk about sex hormones, you know, menopause, for example. And I think that there's definitely something there. Like, the sex hormones do play a role in how much fat you, you, you gain and lose. It's, it's just a fact. And this is another part of this whole calories thing that I always find incredibly, like I don't understand how any serious scientist can think about calories as the only thing. 'Cause think about adolescent girls and boys, okay? So pre-puberty, girls and boys are roughly the same sort of weight and body fat and so on. Then you go through puberty, and women, in general, are have about 50% more fat than boys. It's not that they have less willpower, like obviously not. The difference was that the boys had a bunch of testosterone, they gain more muscle, whereas women tend to develop fat in their hips and their breasts, right? It's, it's just that's physiology. That's the difference between exposing somebody to a lot of estrogen versus testosterone. But it's not a willpower problem. It's not a problem with their diets necessarily, right? So, so it's not like, you know, and, and this is, you know, people who say, "Well, you know, it's all about willpower." It's like, well, then you must think that women have less willpower than men. It's like that, that, that's not true. Like, it's not true in any sense. So therefore, it's the sex hormones that play a huge role. Women do have a difference in sex hormones and during menopause. So we know that there's a certain number of changes, and that may play a ra- role in weight loss. But there's nothing you can do about it. Like, I, I'm not gonna [laughs] change their menopause, so therefore you just have to deal with it. So does it mean they can't fast? No. Does it mean they may respond differently than men? Yes, absolutely.

Dr. Rangan Chatterjee 1:34:32 Yeah.

Dr. Jason Fung 1:34:33 Uh, they may take a little bit more time because their bodies had been programmed, pro- programmed by nature to carry more fat. That's not their fault or anything necessarily bad, it's just physiology.

Dr. Rangan Chatterjee 1:34:46 Yeah.

Dr. Jason Fung 1:34:47 That's the hormones, uh, speaking.

Dr. Rangan Chatterjee 1:34:49 Uh, and I think, you know, all these things are very individual, right? [laughs] Some things work well and quickly to some people, some things don't. That's, it's kind of the way it is. And then also, we have to be careful about how we're measuring the impact. I mean, if weight loss is the only metric people are looking at, they may think that intermittent fasting potentially has failed for them. But actually, the benefits, as we've touched on, on multiple occasions throughout this conversation, go far beyond just weight. So there are, there are implications for your gut function. Often I've found people with IBS-type symptoms say it really clears up massively when they have periods of fasting. Sleep can improve. You know, all kinds of things. Other things can benefit. So, you know, I definitely encourage people to experiment and see. The other thing, Jason, that often comes up with fasting, particularly these days, is the issue of eating disorders, which, as you know, are rampant. They're on the rise, particularly in adolescents. You've released a video on this recently, I saw on your YouTube channel, which I found really, really interesting. What is your view on whether intermittent fasting, whether me and you having a conversation like this is toxic for people who may be suffering with eating disorders? I mean, what, what is your view on that?

Dr. Jason Fung 1:36:08 Yeah, and, and this, the literature really says that there is not a lot of, um, danger with that. So when we're talking eating disorders, generally we're, we're talking about anorexia nervosa and bulimia. Those are the two big sort of eating disorders. So they've done studies, um, where they've basically looked at it. So they, they take people not, you know, um... There's, there's two, two main concerns, right, with dieting or fasting and, uh, eating disorders. One is that you're gonna be so hungry that you're gonna trigger, like, um, overeating or binge eating. And two is that there's, maybe you don't take enough, um, you know, amino acids and tryptophan, therefore you're gonna get a little bit depressed, and then therefore you're gonna overeat. Well, neither of those, uh, possibilities turned out to be true. So in the studies, what they did was, there's one study where they looked at this, uh, where they had people, they fasted them, and then said, you know, "What are your levels of hunger? Do you overeat?" And so on. And, and the bottom line was that ye- people tend to eat a bit more the meal after a fast, and this is a 24-hour fast. Um, but if you look at the full 24 hours, they're still not eating nearly as much as they used to. And then two was that, uh, they did, you know, they took people with diagnosed anorexia and bulimia, this was a separate study, um, and they, they, they, again, put them through fasting, and they, they were basically wanted to see if this was going to trigger their eating disorder. And again, the conclusion from that study was that it did not. So it sounds like it's a plausible concern, and, you know, I don't want to minimize it-

Dr. Rangan Chatterjee 1:37:50 Yeah

Dr. Jason Fung 1:37:50 ... because eating disorders is a very serious problem, of course. Um, but the available data so far hasn't, um, hasn't really, uh, borne out the, the danger that it does.

Dr. Rangan Chatterjee 1:38:05 Yeah.

Dr. Jason Fung 1:38:05 Uh, like, it, it doesn't suggest that there is any danger from that. Uh, you know, I wanna just be careful because there's just not a lot of research-

Dr. Rangan Chatterjee 1:38:13 Yeah

Dr. Jason Fung 1:38:13 ... into that. And I always wanna be careful because- You know, fasting is a tool, and tools always, they can help or they can hurt. It's not the tool, it's how you use that tool. So if you use a, a, you know, a blade, you can cut out a tumor, for example. You can cure somebody, but you can also kill somebody. So-

Dr. Rangan Chatterjee 1:38:32 Yeah

Dr. Jason Fung 1:38:33 ... if, if you're talking about intermittent fasting, like in, you know, somebody, you know, you have a 16-year-old girl who weighs, like, next to nothing with a BMI of 15, no, you do not wanna be talking about it. But you have a 60-year-old man with Type 2 diabetes who weighs sort of, like, you know, has a body mass index of 45, well, then, yes, absolutely you wanna be talking about it.

Dr. Rangan Chatterjee 1:38:58 Yeah.

Dr. Jason Fung 1:38:58 But it's the skill of the person using it. So, you know, you have to choose your situation. Like, to say that fasting is bad for everybody, well, that 60-year-old man who's, you know, super, super, you know, morbidly obese, his risk of anorexia nervosa is almost zero. Like, there's no reason not to talk about it with him. The risk of a 16-year-old girl who weighs almost nothing and has a BMI of 16, yes, the, h- her risk is extremely high. You should not be talking about that with her.

Dr. Rangan Chatterjee 1:39:30 Yeah.

Dr. Jason Fung 1:39:30 So, you know, it's, it's, it's, it's not the knife, it's the way you use-

Dr. Rangan Chatterjee 1:39:34 Yeah

Dr. Jason Fung 1:39:34 ... that knife. And fasting's exactly the same.

Dr. Rangan Chatterjee 1:39:36 Yeah, it's, it's a great point.

Dr. Rangan Chatterjee 1:39:39 HbA1c is a common blood marker that many people get done at their doctor's, which is a, you know, an average measurement of our blood sugar over the past two or three months. With all your experience, of course, if it hits a certain point, we call that Type 2 diabetes. If it hits a slightly lower point, we call it prediabetes. Do you have a sense these days of what an optimal level might look like for someone? I, I understand that you deal with a lot of Type 2 diabetics in your kidney clinic, and you help them put their Type 2 diabetes into remission, certainly get them a lot better using the things that we're speaking about. But I, but I, I've often thought in medicine that we, it's very black and white. You either have prediabetes and Type 2 diabetes, or you're normal. But clearly that's not the case. This is a, a progression, that at some point you flip into prediabetes, and at some point you flip into the Type 2 diabetes diagnosis. So do you have a sense of what an optimal level might look like for someone who's trying to safeguard their health for the future?

Dr. Jason Fung 1:40:47 Um, if you look at studies, really the lower the better. Um, and I think that those definitions are mostly because, um, the, the whole, um, the whole thing is that you have to have definitions to do studies. So you need to classify. So 6.4 is not diabetic, but 6.5 is diabetic. Like, the, the difference is very small, but at some point you have to draw that line.

Dr. Rangan Chatterjee 1:41:14 Yeah.

Dr. Jason Fung 1:41:15 And it's an, it's an artifact of, um, doing studies. So you have to classify people, 'cause you can't just say 6.1, 6.2,6. You can't have like, you know, 15 different categories [laughs] in a study. It'd be really confusing. So, so you break it up and you say, "Okay, well, at 6.5 you're this, and 6.0 to 6.4 is this, and less than that." But it's really a continuum. So there's no real best number. In clinical practice though, I've seen a lot of people, um, who are, like, 5.9, 6.0, and they seem to do fine. What I think is important from an individual basis too is not just the level, but also the stability of that level over time. So I've actually seen a number of people, and I always thought this was, wow, you're, like, almost prediabetic or you're prediabetic, but they actually just trundle along just fine and they're always at 6.0. And I think that that's another thing that I'm not sure is captured with the actual number, is sort of, if they've been like this for this many years, is it really bad or is it not? I actually thought this because it was a relative of mine who I tracked relatively closely for, like, 20 years. And it was, like, 6.1, 6.0, 6.1, 6.0, and they did fine. They'd actually never had any problems [laughs]

Dr. Rangan Chatterjee 1:42:36 Wow

Dr. Jason Fung 1:42:36 ... whatsoever. And, and I thought, I wonder if it's just... Like, their diet didn't change, their weight didn't change, and they're pretty healthy, uh, throughout. But I just always wondered, is it really bad, or is it that person who goes from 5.3 to 5.5 to 5.7 to 6.0 to 6.2? Maybe that's what's bad.

Dr. Rangan Chatterjee 1:42:55 Yeah.

Dr. Jason Fung 1:42:55 So I think, you know, there's two things. One is the actual level, and two is, if it's at a sort of borderline level, is it going up or is it sort of stable? Because what's really gonna be bad, of course, is when it goes up-

Dr. Rangan Chatterjee 1:43:08 Yeah

Dr. Jason Fung 1:43:08 ... over, uh, 6.5. Then clearly you're in the abnormal range.

Dr. Rangan Chatterjee 1:43:12 No, I th- that's super interesting, and I, I suspect over the next few years we'll get a lot more clarity on this as science in this area progresses. Um, Jason, had we had more time, I was wanting to get into your latest book, The, uh, Cancer Code, which is just brilliant. Maybe I can tempt you with a part two at some point, uh, in the future, because I think the way you've articulated your thoughts on cancer and how our understanding of it is developing is pretty profound. And, and it's a brilliant read for anyone. To finish off this conversation, we've covered a lot so far. This podcast is called Feel Better, Live More. When we feel better in ourselves, we get more out of life. Right at the end now, Jason, in all your years of experience, yes, in clinic, but also, you know, spreading information on the web, through your books, what are some of your very best tips for people who have heard what you had to say, go, "Right, I'm in. I wanna make some changes. I wanna start looking after my health. I wanna start lowering my insulin"? What practical advice have you for them right at the end here?

Dr. Jason Fung 1:44:19 Um, I think that the, the, the most important thing, I think, is to focus on sort of foods and less on nutrients, like carbs or, you know, that kind of thing. Focus on the sort of eating whole foods is, is still probably the most important thing, whether it's a carb or whether it's not. I think that's still probably the biggest thing. We don't talk about it as much as we probably should, right? In the whole, uh, thing about carbs and, you know, keto and this diet and th- that diet. It all winds up in, you know, vegetarianism and that, so it, it always comes back to eating sort of natural foods and eating in a way that's not constantly stimulating. So, you know, to me, it's, it's relatively simple and not that controversial. One, don't eat too much sugar. I don't think that's very controversial. Two, try to eat unprocessed foods, which I, again, I don't think is all that controversial. [laughs] And three, don't eat all the time. Like, if you're overweight, don't eat all the time. Like, cut out those snacks. Which I, you know, to me, just seems like, hey, this is just what it was in the 1970s. Like, there was none of this count your carbs, count your calories, count this, count that. Eat whole, unprocessed foods, whether it's, you know, vegetables or even meats. Enjoy your foods when you do eat them, but don't eat constantly. Give your body a break once in a while from eating so that you can digest your foods. Like, that's all your grandmother ever wanted to tell you. Like, give your body a chance to digest the food that you ate. Don't just keep shoveling it in. You gotta use it, because when you're putting it in, it's gotta come out at some point. Otherwise, you're gonna get into trouble. So those three things, I think, are sort of still the core of everything, without getting too complicated. Don't eat too much sugar. You know, eat unprocessed foods, and don't eat all the time.

Dr. Rangan Chatterjee 1:46:21 Great advice to finish off. Uh, Jason, wanna acknowledge you. You're doing fantastic work. You're helping so many people. Think your books are fantastic. Which books would you draw people to, and where else can people stay in touch with you if they wanna keep up to date with your work?

Dr. Jason Fung 1:46:34 Yeah, so I think the best place to start is The Obesity Code. It, it sort of goes into the science of weight gain and weight loss. Uh, I have a number of YouTube videos now which sort of covers a lot of that material in sort of less than 10-minute chunks. Um, so I think that's, that's what I've been doing sort of the last year to, to, to sort of help spread the message. And, um, uh, the other, the other ones, you know, you can also follow me on Twitter, uh, @drjasonfung. And then, uh, you know, but, but The Cancer Code, uh, just to address that, I actually think is the most interesting [laughs] of them. To, to me, it was the most new information, uh, about cancer. But not, it, it, it doesn't follow along with diets and insulin and so on quite as much as the others. It's more of an exploration of sort of what this disease is. To me, that, which is a, you know, and, and, and actually a really fascinating, uh, story. But it's not, it's not gonna change in terms of what you do with the medicines that you do.

Dr. Rangan Chatterjee 1:47:35 Yeah.

Dr. Jason Fung 1:47:35 It's not a diet. It's not completely a dietary disease, so therefore it's not a dietary solution. As opposed to, say, the, the obesity and diet type 2 diabetes, which are dietary diseases. So The Obesity Code, The Diabetes Code are both, uh, there to, you know, just for you to get more information about that.

Dr. Rangan Chatterjee 1:47:54 Yeah. Thanks, Jason. Thanks for your work, and, uh, hopefully get you back on at some point in the future. If you enjoyed that conversation, I think you are really going to enjoy this one with a brilliant cardiologist who uses fasting to help his patients.

Speaker 1:48:07 I've been a cardiologist for 30 years, and I've tried everything. But when I tried fasting, I started seeing changes. People began to lose weight. People's blood pressures came down. Diabetes got reversed.