Harvards Exercise Professor If You Exercise Like This Youre Destroying Your Body

TITLE: Harvard’s Exercise Professor: If You Exercise Like This, You’re Destroying Your Body. CHANNEL: Daniel Dushy DATE: 2026-04-20 ---TRANSCRIPT--- Oh, I’m going to get in real serious trouble for this one. Look, I mean, the given moment of time, you have in your bloodstream about a teaspoon of sugar. And if you get up to a teaspoon and a half, that’s actually toxic.

Well, in a kind of paradoxical kind of cruel twist of fate, getting fatter from sugar makes you actually eat more. A vicious cycle. It’s a vicious cycle. Exactly. I mean, the evidence is very clear that we’re going to what scientists call the physical activity transition. How do you explain that transition? Well, it’s machines, right? It’s the change in lifestyle, right? In our evolutionary history, we were selected to become extremely physically active. You take me and you put me in the North Pole, I will not be very well adapted to handling the cold environment, right? By the same logic, my body is not very well adapted to not being physically active on a regular basis. Our lifespan is being way above the paleative wall. So, well, actually, so that’s another misconception that people have. So, there’s a distinction between lifespan and health span. So, how long you live is not necessarily how long you’re healthy. What do you think or what can you say that it’s your mission? Look, here’s how I would think about it. Well, okay, that’s fascinating and I want to dive into that even more. What is the biggest mistake that people make when they exercise? [laughter] Um just not exercising. I mean um so for example um one statistic I love to repeat um is that if a woman gets about 150 minutes of exercise a week that’s 21 minutes a day of just brisk walking she can lower her lifetime risk of of breast cancer by between 30 and 50%. Wow. People who get about that much exercise can lower their lifetime risk of Alzheimer’s by 30 40%. and and more exercise has even bigger effects. Why don’t people know this, right? That’s what I think is most astonishing that that we all know that exercise is good for you. I mean, that’s like, you know, you don’t have to have a professor tell you that or a doctor tell you that, but people, including a lot of people in the medical world, don’t know how much benefit it is and also why it’s so beneficial. Wow. Can you please elaborate more the about the benefits? Well, I mean, it’s I could go we could go on for hours and hours and hours and hours. We could go for days. So, I mean, you know, I mean, there’s probably no system of your body that isn’t affected by physical activity. Yeah. But you said that the example that you gave with a woman is about walking, right? So, walking counts as physical activity just as much as lifting weights. Well, I mean, there are different kinds of physical activity, right? And they have different benefits, right? And different costs as well. Nothing is for free and exercise is is no different, right? There are costs and benefits to everything. But um in general um in the exercise science world, people divide uh physical activity between aerobic physical activity or what what’s often called cardio and strength physical activity or resistance physical activity. And obviously it’s a it’s a somewhat false dichotomy, right? or it’s an extreme dichotomy because lots of exercises or physical activities involve a little bit of both, right? Like if I like I like to do some rowing. I I’m I enjoy rowing a few times a week. Oh, really? Rowing? Yeah. And rowing is um is both aerobic but also resistance, right? Um uh whereas if I just lift weights, that’s pretty much just resistance. Although you can do um what’s called circuit training, you can do weightlifting in a way that also has an aerobic component. So there’s no it’s a little bit of a an overly generalized you know overly kind of the distinction is not complete but but but they have different effects. So aerobic physical activity has of course lots of effects on your cardiovascular system. It also affects metabolism. It affects you know you know cells throughout your body in all kinds of ways. uh strength physical activity is more localized to muscles but also has effects on metabolism in different ways by say increasing muscle mass and and you know all all of these different kinds of physical activity have different effects and so there’s no it’s hard to you know generalize in a simple way but the important point is that most forms of physical activity have wide ranging effects throughout your body on almost every single system of your body and um and um and they and and that that are by and large extremely beneficial. Well, okay, that’s fascinating and I want to dive into that even more, but let’s just say you are one of the worldrenowned experts of human physical activity in evolution in science. Some people think that maybe. Yes. Yeah, I do. So, thank you so much again. So, where does the evolutionary science comes into this equation? Well, I mean evolution is important because it explains why things are the way we are, right? We weren’t designed, we weren’t engineered, we evolved. I mean, not everybody believes that, but but they that that’s not a scientific explanation. I’m a scientist, right? So, science, you know, evolution is is a is the science scientific theory of how and why we are the way we are. And and if you want to understand how the why we way we are, you need to understand that evolutionary history, right? And um and humans are so all animals evolve to be physically active, right? I mean, u they have to move around to to get dinner and move around in order to avoid being somebody else’s dinner and that sort of thing. But humans had special selection because we evolved from uh apes, right? We evolved from chimpanzeee like creatures. And chimpanzees and most apes are actually extremely inactive. They um they spend about half as much energy being physically active as you would expect for an animal their size. Chimpanzees walk maybe like 2 to three kilometers a day. They mostly rest and eat. I mean, they don’t really do very much. They do a lot of chewing. Yeah. They spend half the day chewing and half the day digesting. They don’t They’re very in inactive creatures actually. And so are gorillas, so are all the great apes. And we evolved from them, right? And during our evolutionary history, we went underwent serious selection to become hunter gatherers. And hunter gatherers are extremely physically active. Typical hunter gatherers walk 10 to 15 kilometers every day. They dig, they climb, they you know they do all kinds of stuff right without machines. And so our evolutionary history uh in our evolutionary history we were selected we were we to become extremely physically active. In fact we’re more physically active than most mammals of our size about 30 to 40% more more physically active. And um and so but that physical activity has had effects on our biology. And so from an evolutionary perspective, if you suddenly become as inactive as a chimpanzeee, which is what basically a lot of humans are today, that’s what we call a mismatch. Um, a mismatch is when you mismatch diseases or mismatched conditions are are conditions or diseases that are more common and more severe because our bodies are inadequately or imperfectly adapted to uh that condition. So a simple example would be jet lag, right? If I get on an airplane and I fly to I don’t know somewhere like Asia right on the other side of the planet my I I I will be poorly adapted to that time change right we all know jet lag right um that’s a similar example or if you take you take me and you put me in the north pole I will not be very well adapted to handling the cold environment there right um by the same logic I’m actually my body is not very well adapted to not being physically active on a reg regular basis because when I’m physically inactive ive I don’t um I don’t turn on all kinds of repair and maintenance mechanisms that keep me healthy. I end up allocating more energy to body fat to to reproductive hormones etc. All kinds of things happen that that can cause me to be more likely to get sick and and um and die young. Yeah, that’s fascinating this mismatch. And how do you see the the current statistics if you have some about how does it spread around the world? Is it is it fair to say that like we are going backwards towards being more like a chimpanzeee in the physical activity side of things? Oh, I mean yeah they I mean the evidence is very clear that we’re going to what’s what what what’s what scientists call the physical activity transition. So we’re studying this for example in in Africa right where my my colleagues and I have been looking in Rwanda and in Kenya and places like that where we’re looking at at how physically active people are in in rural areas. These are farmers who who who who you know produce their own food without the help of machines. They have no running water. They you know they work really hard, right? And then um and as as Africa is modernizing, as Rwanda for example is modernizing, people are moving to the cities and all of a sudden they have supermarkets and they have uh taxis or you know they have these motorcycle taxis where people take all over the place and and they have um and they you know they don’t have to walk up and down every day to you know get food and get they if they want water they just turn on a tap. Whereas in the rural area, if you want water, you have to go and go to a stream or a or a well or a or a spring and fill up your water container and you have to carry it home. It’s huge amount of effort, right? Now, you just turn on a tap and water just comes. It’s like magic, right? And so, we can show um you we can measure that people are becoming way less active. So typical person in Rwanda for example um uh the farmers that we’ve measured are actually some of the most physically active people in the world. They’re spending huge amounts of energy every day just moving around. Some of them taking 20,000 or more steps a day. We actually had one woman who was taking 40,000 steps in a day. One one woman in our sample. I mean that’s like a marathon, right? Um and it’s all up and down, right? And then in the city, the Rwans in the city of Kaggali, which is the capital city of Rwanda, are as inactive as your average American. So this is happening overnight. It’s a instant transition, right? Why? How [clears throat] do you explain that transition? Well, it’s machines, right? It’s the change in lifestyle, right? You have if you go from being a farmer without electricity and without trucks and tractors and cars and and plumbing and electricity and all of a sudden you live in a city, you you you know, all of a sudden you don’t have to be as physically active and and and unless you have a unless you decide to go for a run every morning um or or do exercise, right? Um you will have many fewer steps a day, you’ll just be you you’ll just be less physically active. And and I mean it’s not too complicated of course. Yeah. The thing while reading your book, the thing that astonished me the most is this mismatch. It’s the fact that we are not adapted in many many ways beside physically being active. It’s also the way we consume media and everything around us makes our uh ancient brain go nuts perhaps. Um, I I wanted to ask what’s the most alarming thing that you think that you see about this mismatch? We’re mismatched to eating huge amounts of sugar. We’re mismatched to to social media. We’re mismatched to to lawyers. We’re mismatched to, you know, most politicians. We’re I mean, I could go on, right? I I’m sure anybody watching this or listening to this can come up with their own set of mismatch. It’s not a very complicated idea. Um, but, you know, we also need to be careful about mismatch. It’s not just because something is new doesn’t mean it’s a mismatch. And just because something is old doesn’t mean it’s good for us either. So sometimes people take the the theory of mismatch a little bit too simply. It’s a it’s a scientific hypothesis that we have to test. Like for example, oh I don’t know, refrigeration. Um you could argue that, you know, I mean, you know, refrigeration is a completely modern thing. We’re a mismatch to it. And I would [laughter] I would consider quite the opposite. I think I’m very glad I have a refrigerator. My food doesn’t go rotten. Um um antibiotics are another interesting example. I mean in to some extent they can be mismatches. So people can get sick from antibiotics. We can have negative effects on our microbiome. We can you know there can be you know negative consequences to antibiotics. But a lot of us wouldn’t be alive today uh if it hadn’t been for the invention of antibiotics. So so we need to be careful about about overly simplistic um it’s what what’s often called the naturalistic fallacy. The idea that if something’s this is the problem with a paleo diet, right? If you know the idea that we since we have evolved to eat paleolithic foods, we should it they must be therefore best for us. Yeah. The the the thing is that I think most people if they have anything to reject to the these ideas is the fact that our lifespan is been way above the paleolytic world. So well actually so that’s another misconception that people have. So, it turns out that um hunter gatherers uh tend to live about seven decades. Um and it’s it was after the origins of of farming that lifespan started to shoot down, right? And and and we need to make a distinction between uh um life expectancy at birth and median longevity. So, so um it turns out that you know a lot of huntergather children die a fair number die early on, right? But after you correct for infant mortality, they tend to live to be about 70 or sometimes up to 80, right? So, and which is actually not too far off from from from western countries. Um, so once you correct for infant mortality, actually, we’re pretty much, you know, we’re a little bit we’re doing a little bit better than hunter gathers. Um it was in the origins of farming that people started dying off like in droves because when people started farming they started living in villages with animals you know rats and mice and living next to their their their sheep and their goats and their cattle which gave them diseases. They were also because they were sedentary and living impermanently in villages they were surrounded by their by their filth. So there’s you know all kinds of um uh sanitation problems. That’s when people’s lifespan went went down. And it’s only with the invention of sanitation and various other which has had really had the most effect on human uh life expectancy that people we’ve gone back up to where we were and now we’re a little bit bit better. But the other thing you need to understand is there’s a distinction between lifespan and health span. So how long you live is not necessarily how long you’re healthy, right? And so I think and in the before modern medicine, your health span determined your lifespan. there was no doctor to keep you, you know, alive after you got really sick, right? Um, and so if you look at the effects of uh diet and physical activity, they they they have strong effects on health span which then have effects on lifespan, but they’re they’re contaminated in a way by modern science. For example, if I have heart disease or aththeroscerosis or hypertension or whatever from my bad lifestyle, I can take all kinds of pills that can keep me going for longer than I would have been the case, you know, you know, a few hundred years ago. So, so, so, so the average American, for example, today has an a lifespan of about 78 79, but the average American’s health span today is about 63. So the average American is living 15 16 years after their in chronic illness. That’s the average. So that means there are plenty of people who are have more. It probably has something to do with retirement as well. Am I Well, I mean it’s diet and physical activity, right? It’s it’s and and smoking to some extent. You know, those are the things those are the key look if you if you know I mean I mean you don’t need me to tell you this. Everybody knows this already. It’s well known. you know, if you don’t smoke, if you don’t drink too much, if you exercise and eat an a reasonable diet, you’re much less likely to get a wide range of diseases um that that um that of course are often chronic diseases. Think about heart disease and and um um you know, diabetes and you know, some cancers etc. that can last a long time and um um and just those just few changes to your lifestyle can have huge effects on your health span, hence your lifespan. Yeah. in this matter. I just read a book. I’m I’m sure you’ve read it as well. Meditations by Marcus Marcus Aurelius. Oh yes. Yeah. He buried six sons before he had an hell. So it’s he tells us a lot about the ancient world. Yes. Well, Marcus really and he was the emperor of Rome, too. Yeah. And he was the emperor. Yeah. life life back then was because of especially because of contagion because of infectious diseases was much more um you know it doesn’t matter whether you’re you’re an emperor or a or a peasant you were much more likely to die especially when you’re young. Yeah. So this is infant mortality which is the cause for the way we see lifespan being correct. Yeah. So so if you’re looking at you know really it’s important to correct for infant mortality when you think about about the effects of environment on on your health. Yeah. So I I want to go back. You mentioned sugar and sleep uh which are a big components of health. Can you please elaborate more and why modern people are you know I would say if there’s any one um food that’s causing um people to become sick, it’s the it’s the increase in sugar and and also refined carbohydrates. So white flour, things like that. And and we know why it’s not even a it’s not even that, you know, it’s not that complicated. I mean, we evolved to eat carbohydrates, but we evolved to eat foods that were whole and with lots of fiber in them, but now we remove the fiber from our food, like we mill our flour, so the so the the the the fiber is gone and actually a lot of the nutrients and the protein is gone, too. Or we we have sugar. Now, back in the old days, right, like how would you get anything sweet? You you could have honey or fruit and most fruits aren’t that sweet, right? And you also can’t eat that much of them, right? So, and now, of course, today people have gone from eating, you know, a few maybe a kilo or so of of sugar a year to to, you know, like 100 kilos a year because it’s added to everything. It’s added to our to our drinks. It’s added to our food. It’s, you know, we bake with it. We make all kinds of foods with sugar. They took an Advil in in the United States and it add sugar on it. I was amazed there’s sugar on the Advil. I didn’t know that. [laughter] Okay. Yeah. Well, I mean, you know, helps the medicine go down, right? So, uh we we add sugar to everything. And um and what sugar does among other things is that it um it affects our metabolism. So, it affects our digestion. So, when you have foods with a lot of sugar without much um fiber, you digest the sugar really rapidly. That causes a spike in your blood sugar level. that blood sugar then um overwhelms your system. You end up producing a huge amount of insulin to to get that sugar out of your blood. Do you know at a at a given moment in time I I’ve [snorts] I’ve done the calculations and other people have done it as well. But at a given moment of time, you have in your bloodstream about a teaspoon of sugar. And if you get up to a teaspoon and a half, that’s actually toxic. So our our bodies have to regulate the amount of sugar in our bloodstream really precisely. So if you have too much sugar in your bloodstream, your body immediately gets produces insulin or tells your your to your your pancreas to release the hormone insulin to get that sugar out of your bloodstream. But if you have a lot of sugar really fast, which is what happens when you have, you know, processed foods, you you overproduce the insulin. So then you have a sugar crash. So that does two things. One is that makes you hungry. So then you end up eating more. So then you keep eating more and more and more and more. But also that sugar goes into your fat cells. Your fat cells your fat cells convert that sugar into fat. And and we’re our our our metabolisms are elegantly and beautifully adapted to convert excess energy into fat. And but as fat cells swell, guess what they do? They suck up more sugar. So it makes you hungry. So, in a in a kind of a paradoxical kind of cruel twist of fate, getting fatter from sugar makes you actually eat more. Um, so a vicious cycle. It’s a vicious cycle. Exactly. So, um, so, uh, so sugar is really a major there’s just I mean it’s there’s a lot of data to show this. Sugar is a major, it’s not the only, but it’s a major component of why so many people around the the world today are are are are gaining too much weight or either have obesity or or overweight. Um, it also causes a range of other uh metabolic problems. Um, so um so we pay a price. So that’s a mismatch. We’re clearly not adapted to eating foods that are filled with sugar with with no fiber. Yeah. In the case of um obesity and diabetes, do you think that the the epidemic of it is caused by too many too much sugar that we consume or is it the other way around? Oh well, I mean there’s no one cause to the obesity epidemic. I mean, you try to oversimplify it, you’re going to get it wrong. But there’s no question that one of the components to obesity is is that we have more more food, you know, we have way more sugar in our food, way more processed food that also has a lack of fiber. It’s not just the sugar on its own. It’s the combination of sugar plus fiber because when you eat foods that have fiber in them, fiber slows the rate at which you absorb and digest sugar. So, enables your body to handle that sugar much better. So, and also you know we have junk food which also has more fat in it and fat has calories you know we we we we have very cheap processed food which probably get us to you know encourage us to eat more than we might otherwise eat. Um we’re less physically active. I mean there’s there’s many there’s many you know our microbiomes have effects. um obesity. There’s many many many causes to obesity and and and and it’s never a good idea to try to say it’s just one thing because it’s never just one thing. But but is it fair to say that uh it’s a it’s a feature not a bug in our evolutionary biology? If we if you take a person from the panalytic world and you put it in this environment, obesity is a given outcome. Well, I mean there are lots of people today who aren’t obese. I mean, I’m not obese, right? Yeah. But you need to work perhaps for it. Yeah. Well, I mean, there’s also variation. Some people have higher metabolisms. It’s complicated, right? But excuses for trying to simplify things. Well, but that’s part of the problem is that we try to oversimplify complex things and then people get skeptical about about about because, you know, we we say, you know, like my you know, we all know people who eat a lot of sugar and they’re fine, right? So, it’s it’s complicated, right? uh like for example in uh you know I work in in Kenya there are athletes in Kenya right who eat vast amounts of refined carbohydrates I think by one study like 75% of their diet is is like simple carbohydrates because they’re but guess what they’re running you know 150 kilometers 200 km a week right so and that changes not only how much energy they’re spending right you know they’re spending a lot more energy than than than than than I am just moving around obviously but it also affects their their hormone hormonal response to the same food. So people who are very physically active, if you take two people who are have different physical activity levels, one person who’s more physically active, one person who’s less physically active, you give them the same food, the person who’s more physically active will have a less of an insulin response to the same food because it changes our our our hormonal response. So it’s it’s complicated. There’s no simple simple simple answers, but but there’s no question that sugar and refined carbohydrates have had a massive effect. I would say the dominant effect on on the increase in obesity. Yeah, thank you for correcting me and uh I’ll try to not simplify the complicated things. Uh but you mentioned metabolic diseases. How about cancer? Well, cancer is complicated, right? Again, there’s no one cancer. There are many kinds of cancer. I mean even you could take a cancer of one organ and you can actually turns out you know there you know it depends on the mutation you know even we may say liver cancer or gallbladder cancer or you know pancreatic cancer but but actually each person’s cancer can be different depending upon which genes are involved in that cancer. So let’s just remember that but but cancer um can have many causes but one of them is energy. Cancerous cells are are sugar hungry right? they they actually prefer to use sugar versus fats to for for metabolic reasons. So high sugar diets can increase cancer simply because um there’s more they can you basically you’re feeding your cancer cells. Secondly, uh cancer can be affected by hormone levels and people who are very physically inactive um can have higher hormone levels than people who are physically active. Uh that for that’s an interesting story there. Um insulin affects cancer rates. So people who have more sugar have higher levels of insulin, higher levels insulin is an is what we call an anabolic hormone. It turns on it makes your cells do stuff, right? It’s a it’s a it’s a it’s a it’s a it’s a growth hormone. And so more growth means more mutations, right? Um so so higher levels of insulin are associated with higher levels of cancer. um body fat, fat um more fat causes cancer because fat cells produce uh molecules called adypocines which um um are um are are cause inflammation and inflammation is when your immune system starts to basically attack yourself and that can cause cancer. So, lots of factors, lots and lots and lots of factors increase cancer rates, but many of them, as we’ve just you probably just been following what I just said, many of them result from changes in our environment. So, cancer is not a a new thing. Cancer’s been around for millions, probably billions of years, but rates of cancer go up with socioeconomic status. as countries become wealthier and more and more people are obese and more people are eating higher higher you know sugary diets and and so on and so forth and are less physically active cancer rates go way up. So we can see this uh across the world as as as cancer rates are very high in in industrialized countries um but they’re um but their other places are are catching up as they become wealthier and more industrialized. Cancer is a disease of energy. Yeah. And so what are the statistics about the places that you explored about the ancient world? Well, I mean it’s very hard to get cancer rates from the ancient world because there was no di you know there were no you couldn’t go to somebody hospital and diagnose somebody with cancer. So we have we don’t have a great idea about cancer rates uh in in in the in the paleolithic obviously or even actually up until the modern medical world but we have some data. So for example in uh in Verona, Italy, there was a a a famous physician named Riggoni Stern who who actually cataloged um rates of breast cancer in in the hospital there and figured out that um that uh it was much more common for example among nuns uh religious women right who of course were not having babies um than among non-nuns for example and he was also showing that cancer you know so so he had like we have some data from and you know even if you correct for the fact that he wasn’t able to diagnose cancer as as as well as we can today we can show that cancer rates in places like Italy have gone way up. Cancer rates are higher among women who are um who have um have fewer babies than more babies. And that’s because of hormones. Every time um a woman has a menstrual cycle she has a big huge estrogen and progesterone surge. And the average uh hunter gatherer because hunter gathers have you know get pregnant have a baby nurse that baby for a while get pregnant again etc. They maybe have five five or so babies over the course of their lifetime. Modern women who are on birth control or whatever average so the average hunter gather has maybe 100 150 menstrual cycles in her lifetime. The average western woman has about 400. So more than twice the number of cycles. And of course, every time you have a menstrual cycle, you have this huge surge of estrogen and progesterone. And that those are motic hormones. Those cause cell division, right? Which increase your risk of cancer. So that’s just one of just many many many factors, right? But cancer is really ultimately a disease of energy because it’s about cells getting more energy to make copies of themselves and they start out competing uh uh uh other cells in your body. That’s basically what cancer is. Wow. Uh this is uh really the the the thing that you just said about the women the the the the difference between modern women and ancient women is fascinating but well let me give you another example. So there’s a study that shows if you looked at breast cancer rates in women from Bangladesh who moved to England women who born in Bangladesh stayed in Bangladesh or and women in who are Bangladeshian ancestry who were born in England and grew up in England. Right? So there these are all um uh women from the same population but in different environments and and being in England just being in England alone increased their risk of breast cancer enormously. Right. So it’s the pop it’s the environment um you know we often spend a lot of effort and time thinking about the genes involved in in in various diseases. You know, I mean, there are all these studies on the genes involved in diabetes and heart disease and this that and the other, but there’s an expression in biology. Genes load the gun, but environment pulls the trigger. And and it’s these are gene environment interactions in which it’s the environment that’s changed. And we need to pay more. It’s not that studying genes isn’t important, but you’re you’re not you’re not you and I can’t change our genes, right? We can change our environment. Yeah. It makes you hopeless. Yeah. But it shouldn’t. And so we should we need to spend more effort and more money and more resources worrying about our environments because um you know the genetics isn’t unimportant but it’s the the environment is is really much more important than we often give it give it credit. Yeah. What about sleep? Well, I mean everybody knows I mean I don’t need to tell you that sleep is important, right? Everybody knows that sleep is important. Although I think we sometimes uh again oversimplify. So I’ll give you an example. Uh there’s a standard story that people say which is that you know Edison robbed us of sleep right that you know when we invented um you know electricity and we have lights and TV and now we have cell phones and and all these sorts of things that keep us awake that that we’re sleeping less. Turns out a bunch of researchers have gone to parts of the world where there are there’s no light bulbs and no TV and no cell phones. So studying people who who are you know still off the grid um living uh you know uh in like you know we’re talking about in the Amazon in in the Kalahari desert uh in in in uh in East Africa the Amish for example you know uh various populations where where people are not you know contaminated as much by by modern you know environments. Guess what how much they sleep? They sleep about six and a half hours. That’s the average. So the idea that you know we used to all sleep eight hours and that and that you know the modern world has has has has caused us sleep last turns out to be a fiction um or exaggerated um uh which is not to say that to trivialize sleep um if you don’t get enough sleep um all kinds of problems happen but but what’s the optimal amount of sleep? It’s kind of complicated probably around, you know, most big studies find about seven hours is about for most people about optimal, but it’s a very complicated phenomenon because it’s variable from person to person. So, what’s best for you might not be best for me and certainly, you know, teenagers sleep more and old people sleep less. And furthermore, remember, we didn’t evolve to live to be hundred. We evolved to have as many offspring as possible, right? So, so what’s optimal for lifespan and health span might not necessarily be what natural selection cares about which is how many offspring you have. Yeah. And you know maybe sleeping less might be bene you know who knows it’s complicated. So so we we tend to kind of exaggerate sleep. The other thing we do about sleep is that we make people really nervous about it. Right. The reason I entitled my book exercise that we make people exercise make them you know nervous and upset and feel judged and and upset about exercise. Well, we do the same thing with sleep, right? What I call the sleep industrial complex. Like we we tell people if you’re not getting eight hours, there’s something wrong. And so people, they buy pills to make them sleep. They, you know, they they get special mattresses. They, you know, cover their windows so there’s no light, etc. You know, if that makes you help helps you sleep better, but what a lot of this does is it makes people stressed about sleep. And guess what stress does? Stress elevates levels of cortisol. Cortisol is your arousal hormone. It’s cortisol which prevents you from sleeping. So when things are really bad, right, like when you know during war or famine or, you know, political unrest or whatever, people’s cortisol levels go up and they sleep less, right? So making people stressed about sleep is exactly the worst thing to do to help them sleep more. And but it’s very profitable because you can make them buy all kinds of stuff. Look, I often say to my students like, “How many of you sleep on airplanes?” Like, and most of them will like, you know, raise their hands like if you can sleep on an airplane, you can sleep anywhere, right? You can you can sleep and and you know, we evolved to sleep in camps, right, where there’s fires and there’s hyenas in the distance and people running around and, you know, all kinds of crazy stuff happening. It’s so much a matter of your of what you decide bothers you rather than what actually bothers you. But which is not to say that things don’t bother us but but I think we need to be a little less judgmental about sleep and be more helpful rather than make people stressed about sleep. Yeah. in your book exercise. I think one of the main things I took is more compassion towards myself in many regards including sleep and exercise itself. But uh would you say and I’m sorry if I’m again simplifying things. Um would you say that 10 hours plus is damaging and 6 hours minus is not? I don’t know. I mean nobody knows. I mean it depends on who you are. I mean look there’s if you if you graph if you take a graph you get large population right and you get data and good quality data because if I ask you how much sleep you got last night you probably don’t know actually you may guess but you’re you’re you’re going to be inaccurate right so but if you get data where you actually measure how much people sleep on the x axis and then you measure health outcome on the y- axis like heart attacks or just how long they live or you know something like that it’s a U-shaped curve right and for most populations The bottom of that curve is about 7 hours, right? So people who sleep 7 hours tend to do better than people who sleep 8 hours or 6 hours, right? But it’s it’s that’s a single line and there’s a lot of variation around that curve. So where you fall on that curve and where I fall on that curve might not be exactly the same. Yeah. Um and um and it depends on your age, your sex, your, you know, all kinds of factors, right? Uh so we need to be a little bit careful about it. Um uh and not again oversimplify. But I think most people know when they’ve got enough sleep. You feel you feel crappy if you’ve not gotten enough sleep and you feel good if you’ve gotten enough. And we all know the feeling of oversleeping. You don’t feel so good, right? So most of us, I think, actually have a pretty reasonable sense. And trying to be more precise than that is probably silly because you can’t run the experiment on yourself and then find out later, you know, what your optimal is for your lifespan because by then you’ll be dead. So, um, you know, just try to get enough sleep and don’t, you know, don’t go too crazy about it. The other thing, of course, is some of these these these curves can be contaminated by by illness. So, for example, if I’m really sick or depressed, guess what? I’m going to sleep more. That’s not because it’s optimal for me. It’s because I’m sick. So, so it’s, you know, it’s very it’s complicated. Yeah. H you mentioned the cortisol. wanted to dive into more of those hormones and the way they shape us in regards of this mismatch. How about dopamine and all these other things that go through our brain and body? Well, dopamine is a neurotransmitter, not a hormone. Sorry to be professor here, but um look, I mean, our bodies are filled with various kinds of signaling molecules, hormones, neurotransmitters, etc. that regulate all kinds of things. Let’s talk about cortisol before we get to dopamine because cortisol is pretty important, right? So cortisol uh is is a stress hormone. Now, and people often get this wrong. Cortisol isn’t higher levels of cortisol don’t cause you to be more stressed. More stress causes your cortisol levels to go up. So if uh you know suddenly a you know somebody screamed fire or you know there was a you know a bomb went off or you know around here, my cortisol levels would suddenly go up. And that cortisol is an arousal hormone that’ll help me um uh deal with the with the crisis. The problem with cortisol is that it’s it’s adaptive for short term, right? Cortisol. So if I go for a run, right, my cortisol levels will go up, tell me get energy, right? So I can deal with my run. But then the problem is that you know, so that’s good. But but we don’t what what’s problematic is when cortisol levels are chronically high because then it can have pernicious effects. So one of the things that cortisol does is that cortisol because it’s it’s an hormone that’s out there to give you more energy to run away from the lion or whatever it is, it’s going to there’s only so much energy your body has. So cortisol turns off other things. So, one of the things it does is it turns off your your your immune system or it turns down your So, when your cortisol levels are high, when you’re stressed, you’re more likely to get a cold because or get in sick because you’re going to turn down your immune system. Uh cortisol also makes you hungry. So, people who are stressed, guess what? They eat more. They have, you know, in the middle of the night, they go to the refrigerator and and and eat whatever, right? Cortisol also causes you to store fat in temporary deposits in your belly. Belly fat, abdominal fat. That fat is the fat that we care about the most because it’s the most in damaging. That’s the fat that causes inflammation. So chronically high levels of cord cortisol caused by stress are are are are terrible, right? and they they cause so people who are suffering from racism, from discrimination, from famine, from whatever have chronically elevated cortisol levels and it and it has serious long-term negative consequences on their health. Okay. Can I um before we go to dopamine and the other things, I myself come from a a war torn place right now. Yes, I was thinking of that. Yeah. And um it let’s say cortisol levels are are high all across the board in our place in my place. Um what is your suggestion for people who it’s like uh you know the world is just making you be more stressed and have higher levels of cortisone? Is it something controllable still in these environments? I mean yes and no. I mean to some extent we can we can try to tune up learn strategies to to not let you know politicians who get us upset and the circumstances around us elevate our cortisol levels. But sometimes we can’t control them. If you’re if you’re in a in a in a if you’re in in the in the you know if you’re subject to famine as a lot of people are in your part of the world and constant stress you can’t just you know meditate your way out of it. Uh so uh so these are real physiological consequences of of of of uh of uh so I mean there’s no simple solution and this you know it’s a lot of these are environmental solutions that are outside people’s control um uh u but some of this some but to some extent people can cope some people cope better than others yeah this is why I’m asking it’s very um uh you can see it very clearly. Some people take it better than others. The the stress of our lives. Yes. But sometimes there’s nothing you can do about it either. If I’m in a if I don’t have enough food to feed myself and my family, do you think I can just meditate my way out of that? Of course. No, no, no. But but there is in the same family. I see it all the time. Some people are reacting differently than others. Yes. Yes. Yeah. So yeah, this is a complicated situation and cortisol just one of those hormones. if you can go over to to dopamine and serotonin. All right. Well, so dopamine is very complicated molecule um is a is a [clears throat] I mean plays many it’s a neurotransmitter in the brain and it plays many many functions but one of them is it’s a kind of a reward molecule. It tells us to do something again or tells us that you ought to do it right and uh so like for example you know in the morning when I go for a run I very rarely want to run. I mean I mean it’s like it’s no fun, right? Um however um after my run um I feel really good about it, right? I feel I usually, you know, it takes me, you know, a kilometer or two and I’m feeling better about my run and I enjoy it and I have a good time and I come back and I’m really glad I did it even though I rarely wanted to leave the door in the first place. and and then and then my um but what that one of the things that that run does like any other um thing that you know behavior that we’re selected for is that that run increases dopamine levels. It also increases receptors for dopamine so that now my body wants another run wants me to stay active. So people who are very active um become sort of addicted slightly to physical activity because they um their bodies um um I need that and if I you don’t want to be around me if I haven’t exercised for a few days. I’m I’m I’m grumpy and grouchy and irritable and and unpleasant. It’s because my dopamine receptors are screaming for more. So So it’s a reward mechanism. Dopamine also goes up for sex or it goes up for eating good food or gambling can cause you know dopamine uh whatever. So it’s complicated but here’s the thing. So it’s one of the reasons why once people you know people are physically active it’s a reward mechanism that keeps us being more physically active. It can also work against us. It can also keep us get us eating more sugar because you can get addicted to sugar and you we need that dopamine craving from your sugar. But here’s the thing. When when you’re overweight or obese, actually really you’re more obese, especially again visceral belly fat, you can actually cause uh insensitivity uh to the receptors of dopamine. So if I go for a run and I I get I get a dopamine hit from my run, but somebody who’s unfit and and struggling with their weight goes for the same run may not get the same reward. And yet we tell people, oh, you’re going to feel great after your run. It’s going to be all good for you, etc. It takes actually if you have dopamine insensitivity, it can take you weeks to get to the level where you’re actually going to get a reward. So, we need to be honest to people about how the system works, right? Oh, we often say that running, you know, exercise is a magic bullet. It’s going to instantly make you feel better. It will eventually make you feel better, but the first few weeks um if you if you’re inactive and you’re trying to get active, it’s going to take you time to get there because your your dopamine system is not going to be the same as the person who’s fit and healthy, their dopamine system. Yeah. So, is it correct that it’s I don’t know if completely, but is it malleable the the things that you can get the dopamine from? You can uh Yeah, sure. It’s it’s very it’s very envir Yeah. I mean, it changes. we have we have some control over it. Um uh not complete control over it but we have some control over it and it’s again it’s environmental and you can change your environment and that’s important again it’s all a gene environment interaction that’s matter but if I hear professor Liberman saying that I need to go for runs or go for walks I can alter my brain to get dopamine from it. Yes, but not not instantly. It’s not going to happen overnight. It can it’s going to be hard work and if you’re unfit it’s going to be harder work than you might think. Yeah. But we need to give people that information so that they don’t get discouraged, right? They think, “Oh, I went for my I climbed I went to the gym as I you know I was told to by my doctor and I don’t feel any better like what’s what’s all this nonsense about it being a a magic bullet, right? I mean it takes time. It takes but eventually you’ll get there but it takes absolute time and you know sometimes I hear the term you know people are exercise addicted and you know people wonder like you know it’s not really I think that’s a really unfair term um um because we’re assuming that if you don’t exercise that’s the normal condition. Yeah. I think being not not now not having no reward system for exercise is to me abnormal. Yeah. Can you elaborate more on this uh fairness because yeah in your book again you said something about uh the in the beginning of going to exercise going to lose fat it’s the it’s going to be harder because you are you don’t feel good about it even yeah but it’s also it’s harder for all kinds of reasons. Yeah. I mean you’re you’re not going to be well adapted. It’s going to you know you’re look I’ll give you an example. My mother when she was uh in her 30s when I was a kid um she uh decided to become more physically active. She was very unfit and um she decided to go running. She decided to run because it’s complicated story but uh the she was a professor at the University of Connecticut and they built this fancy gym um and they wouldn’t let women use the gym and she didn’t like that. So, she decided to become a runner to liberate the gym, but she could run only a quarter of a mile at first. Um, and it was hard and she actually hurt herself. I remember her coming home. She like tore her hamstring or something. It took her a long time to get up to where she could like run a mile. But over time she became and she didn’t like it but she was doing it not because she liked it because she was doing it because she was she was trying to make the gym available to women as well as to men. But eventually she became addicted um and she became a lifelong runner and she unfortunately she died recently but she ran five miles a day for I don’t know 40 50 years um kept her very healthy um um but that took time didn’t happen overnight. Right. Yeah. So, and that’s true for just about everybody, right? That’s her experience is not unusual. Uh, so it takes time. You have to be patient and we need to be patient with other people and not give them false expectations. Yeah, this is an amazing message. And if you can elaborate even more about fat exactly specifically because burning fat and exercise seem to be uh some mis perceptions about the combination of the things. Oh, there’s a lot of controversy. Oh my god. I mean, let’s first of all, if you have a lot of fat, just going for a walk or a run is just harder than if you don’t because it’s like it’s like putting weights on your body, right? It’s extra work. So, somebody who who’s obese who walks a kilometer is spending I don’t know 20 30 40% more energy than somebody who’s not. Um so, and that’s extra hard, right? Um it’s also more loading on your joints, etc. So, that can be tough. But, um but there are other effects of obesity. um and that that obesity causes um uh insensitivity to various hormones. So because obesity causes inflammation, right? Inflammation is when your immune system is kind of on kind of constantly active all the time, right? And it attacks things all over your body. It’s called chronic systemic inflammation. And so obesity has all kinds of negative effects and one of them we just mentioned. It affects your dopamine sensitivity. It affects your insulin sensitivity. So you’re more likely to get diabetes. It can affect sensitivity to another hormone called leptin, which is which affects your your body um um how your body regulates um your your metabolism and body fat levels. It has all kinds of effects, all kinds of effects. Um and um so uh so obesity is a kind of a vicious circle because once you’re obese then it it kind of it uh has negative effects on many many many regulatory systems in your body that that that are affected. But that’s the bad news. The good news is that you can and there’s a big debate about obesity and exercise. So, so one statement you hear all the time now is that exercise isn’t very good for helping you lose weight. Um, and so it’s this is complicated. One of the reasons for that that people say that is that most of the time when people are obese and overweight, exercise is hard. And so when they do experiments where they ask them to do people just do just 150 minutes a week, right? That’s 21 minutes of brisk walking a day. Many people on those experiments failed to do it. So adherence to the prescription is very very low. So if you look at study after study after study the you know that looks at the effects of exercise on weight etc. A large percentage of people in those studies don’t even manage to do the very minimum amount of exercise. And it’s not because there’s anything you know they’re bad people. It’s because it’s hard. Yeah. Right. So so so just to clarify you’re still talking about obese people. is like the Yes, I’m talking about obesity, right? So, um so people have say well you know obesity it’s not exercise is not very good for and so you need to make a distinction between what we call effectiveness and efficacy in English efficacy is how well something works in the ideal circumstance. Effectiveness is how well it works in the real world. And so physical activity has efficacy for weight loss but it has a low effectiveness. But the other issue is dose. How much you have to do. Now, if you just walk 20 minutes a day, that’s yeah, maybe a mile a day, you know, one and a half kilometers, right? Um, that’s about what 50 to 80 calories a day, which is not a lot of calories, right? So, you’re not going to lose a lot of weight. I mean, you just eat a a few peanuts and you’ve got that energy back, right? So, to lose weight, you need to actually exercise a fair amount. And so exercise, it’s true, is not all that effective for losing a lot of weight fast, but there are plenty of studies which show that 300 minutes a week, so 40 minutes a day of walking, people slowly and steadily and gradually can lose weight and and more can be better. But you um but you can lose more weight by dieting. So people sometimes say, “Oh, forget the exercise, just do the dieting.” But that’s a really bad way of thinking about it because for two reasons. First of all, there’s not an eitheror. You can do both. Secondly, the reason most diets fail is not because people can’t lose weight dieting. It’s because they gain the weight back after the diet. The vast majority, if you don’t eat a lot, you will lose weight. But, but most people gain their weight back afterwards. And study after study after study shows that people who exercise during a diet will lose a little bit more weight than people who just just diet. But more importantly, people who continue to exercise after the diet is over are much much much less likely to gain the weight back. So, and we know why. And because not only is it the energy that you spend, but also it changes your insulin sensitivity. It changes your sensitive another hormone called glucagon. I mean it has all kinds of effects on on your on your physiology. So and the dose required to to not gain weight is not the same as the dose required to lose weight. Yeah. So so sometimes people ask you know which is more important diet or exercise and I always answer the same way which is a stupid question. It’s a it’s [laughter] a dreadful stupid question. I mean since when is this a trade-off? You should any diet should include diet plus exercise and you and if you’re going to do it you if you’re going to diet to lose weight you need to think about what’s going to happen after the diet right you need to because you don’t want to have done all that weight loss for no reason right you want to keep that weight off and that’s going to you’re going to be much more effective um if you can include a component of exercise yeah and if I can make the the dist distinguish if I can distinguish between obese people and just regular people like their BMI is not perfectly accurate as the doctor said. What why do you think those people are having trouble losing weight? Is it the same as you just said? I mean all of us have trouble losing weight. I mean weight loss is hard. I mean I mean we are adapted not to be hungry, right? I mean the reason people struggle to lose weight is that is is mostly because of hunger, right? I mean there are all kinds of diets out there. There are lowfat diets and low carb diets and low calorie diets. All of them can work if you stick to them. The problem is that people have a hard time sticking to them or they do lose weight and then it comes back. And the reason people have a hard time sticking to it is because they get hungry. Right? If I didn’t eat enough um if I’m in negative energy balance what a diet is, right? If I’m taking in less energy than I’m using, I’m going to be hungry. Right? That’s what all creatures get hungry if that happens, right? And hunger is extremely hard to overcome. And and it takes serious willpower to overcome hunger. And um and so u there’s no magic bullet. There’s no simple formula. Yeah. Um and people have to figure out how to cope with their hunger uh in order to diet. And and that’s and and and one of the reasons that physical activity helps is that physical activity actually helps you with your hunger. Yeah. Changes your metabolism. And now these days we have OAMIC and other drugs like that which just cancels your hunger. Exactly. And that’s why they’re so effective. And and you know they’re the closest thing we have to a true magic bullet. But remember ompic there are some problems with GLP1s these drugs which do I mean they have all kinds of wonderful benefits. I’m not anti-GLP1, but first of all, they don’t prevent you from getting overweight or obese in the first place. So, people take them after they get, isn’t it? It’s better not to have to take them in the first place. Secondly, if you’re taking them, you it seems so far you have to keep taking them for the rest of your life because once you stop taking them, your hunger goes straight back and you and people tend to regain the the weight. Third, when people do that, they tend to often lose not just uh fat, but they also lose muscle mass. And that can be have really serious repercussions because as you get older, especially, you need to maintain that muscle in order to stay to stay to prevent what’s called sarcopenia or age- related muscle loss, which is a major cause of disability in older individuals. And fourth, of course, it’s expensive. And fifth, they can often have some side effects, right? All drugs have side effects and GLOP1s are no exception. Um and so so GLP1 be GLP-1 drugs have been really helping a lot of people but but um but you know they’re not they’re not the complete total perfect solution that some people like to think. Uh I heard a doctor online said that um uh will you can save your willpower for some things that better improve humanity instead of your hunger. So if it the just helps you with this willpower um it makes everything easy. So u I I you said that the willpower is one of the main components in overcoming anger. Yeah. I mean, I don’t [laughter] I I don’t think I don’t think you can just say willpower. I mean, people also say really bullshitty things about willpower. I mean, as if having enough willpower is just something you can summon up, right? When I’m really hungry, I I’m I’m I’m hopeless, right? If I get really hungry, you don’t want to be around me. I get hangry, right? Um it’s not because I don’t have willpower. I have a lot of willpower. I’m able to do all kinds of crazy things, but I’m not very good at dealing with my hunger. Is that is that is that a defect of mine? So having I know which doctor you’re talking about, but but telling somebody telling us that all you really need to do is conquer weight is willpower is I think insulting. It’s like telling a drug addict. All they need to do is just say no to the drug. We are adapted to get hungry and to eat food when we’re hungry. And having and expecting people just to overcome it with willpower is I think um is not going to work for most people. Yeah. And this is why only a doctor who’s divorced from from reality could say something like that. Oh yeah. I just say that ompic perhaps gives you the well ompic doesn’t give you willpower. It just it turns off your hunger. Ompic doesn’t affect your willpower. Ompic turns off your hunger. So it’s not affecting your willpower. You don’t need your willpower. No. Exactly. So that’s why it works. Yeah. This this is what I’m saying. Yeah. Okay. So this is just amazing. Thank you so much for all the information. It’s incredible. uh in the in this case I just the the thing that uh most people are failing with their diet in losing fat is it fair to say that in what you’re saying I’m hearing that habits make most of it is because well it’s habits it’s it’s lifestyle it’s environment it’s what you have available to you I mean if you’re like you know in many parts of of America right there it’s hard to find inexpensive healthy food right that the the really bad for you fattening food is cheaper. And if you’re on a budget and you’re stressed and you so your cortisol levels already high, right? And you and you have kids and you have you’re commuting long distances and and all kinds of bad things are happening in the world and whatever, you know, you’re going to be more likely to eat the food that’s out there that’s going to um going to then contribute to the fact that you’re more likely to become obese. Yeah. Um people can’t just modify their environment at their own will, right? That’s not easy, right? uh being thin and physically active is now a privilege of of the wealthy and the and others. I mean I I’m very lucky. I have a nice job. I have lots of time. I get to go running in the morning. Um because I don’t have to drive to work long distances. I I amum, you know, I can get I can uh you know, you go to marathons, right? Like big city marathons around the world. Guess who’s running them? They’re wealthy people, right? Um um um you know, ironmen, the triathlons. These are millionaires who are able to do that. You You think flying to Hawaii with your $30,000 bike is like for your average person? Of course it isn’t. Right. So So physical activity and being thin is actually now a privilege of of of of those who are better off in our society. Wow. This is fascinating and I [snorts] never thought about it this way. Um I wanted to go into your uh specific uh uh story or approach to this um field. What made you go into from evolutionary science to uh starting to uh think about exercise and physical activity? Well, it’s a long story. Um I’m not sure it’s that interesting, but you know, I started off as a um you know, I’ve always been interested in human evolution. And when I was a student, I got really excited by studying how and why humans evolved. And I was really I was a skull guy. So I worked a lot on on the evolution of the human head. Um and um uh but I also uh I’ve always liked being physically active and partly because of my mother. Um [clears throat] and I was never a serious athlete, but I just like to hike and run and things like that. And um and in the 19 uh you know you know at some point I started getting interested in in in how we use our heads to stay how we keep our heads still when we’re running. So if you watch somebody with a ponytail running right you watch them running that ponytail goes up and down and side to side. It’s like an accelerometer on the head. So the head is staying pretty stable but there’s all kinds of forces acting on the head that that ponytail is essentially measuring. And so I got kind of curious because I was working on on the on the head. I wrote a big long book called The Evolution of the Human Head that nobody’s ever read. Um big academic book, but I had a chapter about the head and locomotion. And so I started wondering about head stabilization. And I worked and I got interested with a colleague of mine, a guy named Dennis Brambble, a good friend of mine who’s at the University of Utah. And because he was interested in some of the same topics and we we came up with this, you know, Bramble had been very interested in in in in running because a student of his named David Carrier had been working had been interested in sweating and running and long story, but anyway, long story short, I got infected with this idea and we we started studying a a feature on the on the back of the skull called the the nucle it’s it’s it’s a it’s a ligament. It’s really it’s it’s actually a tendon, but it’s called a ligament called the nucal ligament, which is turns out to play a really important role in head stabilization. And chimpanzees don’t have it, but we do. And other animals that run have it. And we discovered that this traces of this ligament first appear in the genus Homo starting around 2 million years ago. You could see it on fossil skulls and that was like a Eureka moment. And so we started working on this hypothesis that there was selection in the genus homo for us to run long distances in order to hunt. And we ended up publishing a paper that was in the journal nature was on the cover um entitled Born to Run in 2004. And so we started studying and we and for that paper we spent years Bramble and I writing that paper. We probably spent about three years writing that paper, putting together all the evidence that humans evolved to run long distances, all the anatomical features, etc., and and making the argument that it was in the genus homo. Um, and when the paper got published, it it kind of went viral. I mean, it it went all over the world. There were like every major newspaper covered it. It was pretty pretty interesting experience. and and um I of course and of course people in my field the paleo anthropologists didn’t like it because they far as they were concerned human evolution is all about walking and this running is kind of stupid what these people arguing this but everybody else the exercise physiology world the exercise science world you know runners I mean I got letters from people all over the world about this paper uh because they were excited by it because we basically made the argument that you know running long distances isn’t this weird thing that just athletes do. It’s something that we’re evolved to do. It’s part of who we are. And it helped didn’t it’s not the deterministic thing, but it helped make us who we are. And um and of course I I immediately started getting interested in in of course running is a form of physical activity. It’s for it’s the most natural form of vigorous physical activity. So walking is moderate physical activity, but running is vigorous. And if we evolved to run, then I started thinking about why is running so healthy. And um I started getting more and more interested in this field called evolutionary medicine. And you know when I’m teaching my classes you know I teach a big human evolution class at Harvard when I teach the students about you know different species you know Australas this and Australus that or these different species of early homo I mean you know they learn it because they’re good students but they’re not all that interested because what what is it to them right but when I start talking about the evolution of running or and how it’s relevant to health or walking it’s relevant to health they start paying attention right because they care about it right matters to them. And I realized and I you know I was having a midlife crisis and so I started writing a book called The Story of the Human Body. And um um I’m not making this up, but the the the file on my computer, the original title of the book, which I was never planning to use for the title of the book, was why should anybody give a about human evolution? Because after all, you know, why should most people care? And the answer is mismatch, right? And you know, what are we adapted for? And one of the things we’re adapted for, it’s not the only thing, is to be physically active. And so I got more and more interested in how evolution is relevant to health and how how it can help people use their lives, make them better, um, than just what happened on its own in human evolution. And and that’s very empowering. Even though it’s led to all kinds of debates and, you know, whatever, ultimately, you know, if you can make the world a little bit of a better place, um, uh, you should, right? And it it’s and you know if we can if I can help people understand physical activity and use evolutionary principles and and diet to help them to to be healthier. I mean uh uh that’s rewarding. Uh so it’s kind of given gotten me excited about doing all kinds of things that I never would have otherwise done and um and so that’s keeps me going. Yeah. Is it fair to say that it was like a dialogue uh between you and the people reading your research and Well, of course. I mean, you know, academics, I mean, there one of the problems with some academics is that they’re they’re doing research that only like 12 other people in the world really care about, right? And you know, sometimes that’s actually can turn out to be very important, but often it’s not. And um you know, I mean, I didn’t I mean, I was writing papers about chins and brow ridges and you know, things like that. And you know, okay, humans have chins and Neanderthalss don’t have chins, but ultimately who cares, right? But but writing about how we evolved to run and why that can help you avoid heart disease, I think most people care, right? sounds like and the evolutionary part is some of your passion towards the field and I imagine that going to Kenya and all these other places looking at the um researching the Paleolithic world in quote unquote was exciting for you personally am I correct? Oh yeah, absolutely. I mean, I I I I’ve been very I’ve been extremely fortunate to travel a lot in my career and and and you know, I still love fossils, you know, but I also care about people, right? And I don’t see a distinction between the two. We are who we are because of what those ancestors of ours were like. And it’s all connected. And so I see I see the relationship between the fossil record and and the people who are alive today as as part of a continuum. Yeah. And do you uh the the specific uh thing about running that you mentioned the the that we adapted to run long miles. What does it say to you about uh about our nature? H what is the consequences of this discovery do you think? Oh gosh. Well, I mean that’s that’s complicated. Look, when you walk out the door, if I leave if I leave this room, right, most of the people I will see will be walking. They won’t be running. So, let’s be first be clear. It’s not all about running. It’s about moving, right? And and so we walk and we run. And walking is the most fundamental form of moderate physical activity, but running is the most fundamental form of vigorous physical activity. And and and vigorous physical activity is just part of the mix, right? If you want to be really healthy, it’s good to walk. I mean, that’s the most important thing. Everybody should just walk a lot. But if you can also occasionally get your heart rate up, that’s also beneficial. And before swimming pools and exercise machines, you know, the ellipticals in a gym or whatever, running is how people got their heart rate up, right? It’s And so, um, and it’s also how we got dinner. Um, and so we have adaptations from our heads to our toes to not just walk but also to run. And they’re not the same thing. Walking and running are are actually biomechanically very different. So running is running is just not fast walking. But also uh running does things for your body that that walking alone cannot do. So um uh it’s incredibly beneficial for your cardiovascular system, for your heart, for your you know for for your for your brain, for Alzheimer’s, etc. Uh it’s it’s part of who we are and you don’t need to you know run marathons in order to get the benefits of running. Um and not everybody needs to run. There are other ways to get vigorous physical activity. You can go to the gym and use various machines if you’re have joint problems or you can swim. I mean people until recently nobody swam laps in pools because pools didn’t exist. And if you were in Africa for most of human evolution and you want to go swimming you have to worry about crocodiles which is not a good thing. So, so um so you know um um so you know running is just part of who we are and and and we can learn a lot about about the benefits of physical activity uh by studying running. What about just uh learning more about who we are in this in the consequence of this discovery? What what does it say about the human nature? I I think I don’t I mean you know I mean look it’s complicated people all kids love to run right you you want to torture a kid prevent a child from running right running is part of play and as we get older a lot of us stop playing right um and why do we play when we’re young well playing when you’re young is an adaptation to help us learn develop capacities develop skills you Um it helps us learn to be better people so we don’t if you the other team scores a goal you don’t punch them right um play has all kinds of benefits but one of them is to is to help us become physically fit athlete adults who can then do things and of course for millions of years that play as a kids help adults be able to run so they could hunt because hunting what we call persistence hunting was very important for evolutionary history. Now we live in a world where we don’t have to run anymore. Children still need to play, but adults no longer need to run. And so now we invent reasons for us to run. Like, you know, I I sign up for various, you know, races like, you know, I just did a half marathon not too long ago, right? And um um but I didn’t have to do that. I did it because I wanted to do it, right? Um but I got a lot of benefit from doing it, right? It was great for my cardiovascular system. It was great for my immune system. is great for all kinds of things in my body, right? Um and and you know, I can tell you um uh standing at the finish line watching people finish after they, you know, a lot of them were people who hadn’t run a half marathon before in their life. Um uh it was called the Great North Run. It’s the largest half marathon in the world. And I can tell you it was a beautiful experience watching all these people who who had never run a distance like that cross the finish line and see just how happy they were. Um they were elated. They were they were high, right? And they were a lot of them ran not just um for themselves, but they ran for charity, right? They were raising money for really good causes. And I think that’s also important because we ran in the past in order to help each other to get dinner to feed our families and to feed other people in our in our group. And so people today are using that same instinct to help each other. They’re raising money for cancer and Alzheimer’s and all kinds of other wonderful causes. Um I think it’s part of the same phenomenon. So we ran not only to help ourselves but to help each other. And I think that’s still the case. And it’s and you know you don’t have to run to do this but there’s no question that um it is uh it has real benefit and real power and um you know really does make the world a better place. Yeah. You mentioned the fact about the rich got the time to do it. Uh I think a lot about the fact that if I’m not mistaken Obama during his administration was getting up every morning to run for an hour at least. uh which makes me humble when I don’t want to go to run. It’s like he ran the world when he ran. So yeah, I mean and and the number one reason people give for not exercising, whether it’s running or walking or whatever it is, it is the people say they don’t have the time. Yeah. It’s the number one reason people give and um and I just don’t believe it. Uh as you say, if Obama had time to do it or to be honest, let’s be let’s be equal. George Bush also ran. I mean, a lot of presidents, Jimmy Carter ran and lots of presidents ran. Trump doesn’t run. I don’t think Trump runs. [laughter] No. But anyway, um um um there’s no question that um uh you know, we all have trade-offs in time, but one thing that running or other kinds of physical activity does is it actually helps your mood, it helps your energy levels, it helps you sleep better, it helps you do all kinds of things. and and you get the time back in in increased concentration and in and in all kinds of and you know in in better mood and better sleep and so it’s rarely actually uh um uh you know look you don’t I mean you don’t have to run an hour a day in order to get the benefits of running but you know even like 20 minutes of something you know can have huge effects on your day and people I always ask you know when students tell me they don’t have time I ask them how much time they spend on social media And they then they usually don’t answer the question because they know full well that they spend hours a day, you know, on their Instagram or whatever the hell they’re, you know, on and they could have spent some of that time um exercising. Well, this time is just one of the uh components of the damages uh from social media. Can you just give us a little bit more because we we touched it. My my instinct is it’s, you know, it has some benefits, but the costs are huge and and we we’re still figuring them out and and and and they’re they’re seriously concerning. Yeah. Okay. So, I I wanted to ask um what you talk a lot about doing good in the world and making it uh a better place even. Um what do you think or what can you say that it’s your mission uh when you in spreading this uh knowledge because you do touch millions of people with with these books and lectures and everything. Yeah. I’m just trying to you know help people. Look here’s how I would think about it right. We I think it’s useful to have a philosophy right. I think everybody needs to have some kind of philosophy. You don’t want to die thinking, gosh, I misspent my life, right? I didn’t use my life. You mean we have one chance, right? You have one chance in this incredible gift that we’ve been given to to live a good life and to and to and to and to make the most out of it. And you don’t want to be on your deathbed thinking, you know, I what did I do? What what did I waste my life on? Right? And you and at the same token, you also got you have one body. I mean, I don’t I don’t have another body. I have the one I was born with and I didn’t get to choose it. It was given to me or determined to me by by accidents of birth and and whatever. And I think we need to have a philosophy of how we use our bodies, you know, to use them as best as possible. And uh and part of that involves uh knowing how to use our bodies and part of that involves knowing an evolutionary perspective because as the expression goes nothing in biology makes sense except in the light of evolution. We didn’t we didn’t we didn’t that my my body wasn’t engineered or designed. It it I I inherited it from my ancestors who inherited it from their ancestors and gone back and back and back and back and back in time. And so understanding that evolutionary history helps us, I think, use our bodies better. And so my job is to try to help marshall the evol evidence from evolution uh to um and integrate it with other kinds of science, you know, medical science and and whatever to try to help people u make better uses of their bodies so that they can get the most out of that’s my that’s what that’s that’s my that’s what motivates me. And you would wish that more people would be interested in the evol evolutionary components of the owners. Well, I think it’ll help them. I mean, I think especially if they’re in medical science, right? [clears throat] You know, there’s so many doctors who don’t know. Look, doctors are can do wonderful things, but they’re also some of the most ignorant people I know because they they they think that they know everything and they don’t and they don’t know why things work. and they also are taught one set of uh skills but they sometimes at the expense of some other skills. know look [laughter] not criticize some I obviously work with a lot of doctors so many of my best friends on the planet are doctors and they most of them will actually agree with me it’s a it’s a medicine is has has a capacity to do great good and also do great harm but it’s also not just medical medicine we overmedicalize a lot of things like medicalizing exercise has failed right a doctor telling you to exercise doesn’t get you to exercise doctors are you know the medical world is is mostly geared towards helping people once they get sick, not preventing people from getting sick in the first place. And the best disease is the disease that never happened. So for example, according to the the Center for Disease Control in the United States CDC, 70% of the medical conditions that Americans suffer from are preventable, right? And that’s probably an underestimate. So why don’t we do more to prevent [laughter] those diseases, right? Many cancers are preventable. I’d much rather not have the can cancer than than have to deal with it in the first place. And if I do get cancer, I will go see a doctor and I will we will do whatever we can. But the best thing to do is not get that cancer in the first place. And how do you explain that it’s not the way it’s happening? Why? Because it’s not why don’t we spend enough energy on prevention. Yeah. Because a bird in the hand is is is actually always worth two in the bush, right? So we we we we engage in hyperbolic discounting. Yeah. We we we we we we have that candy bar today and tomorrow I I’ll I’ll not have the candy bar. We take the elevator today and tomorrow I’ll take the stairs. We we we we we delay all kinds of things that we know are good for us. People who smoke, they know full well it’s bad for them. I’ll quit eventually, you know, or I I’ll just one cigarette now or I could go on, right? And because it’s the urgency. Prevention doesn’t have the same urgency as treatment. So when you get sick, you have an urgent need to treat it. But when you’re trying to prevent something, it’s not urgent. Yeah. My question is not about the the general public, but for the the medical industry. But they’re not paid to do it, right? Doctors aren’t paid to prevent. I mean, how many, you know, like a heart doctor is not paid to treat your hypertension before you get sick. That’s somebody else’s job, right? And we don’t, but the problem is that nobody, it’s really nobody’s job. We have schools of public health. Public health is underfunded. um we you know it’s it’s nobody takes care of this right so so the end result is that lots of people get sick from diseases that they don’t need to get um and then and then we spend vast amounts of money and people die and suffer huge amounts because um from preventable diseases now look I’m not claiming that exercise and diet are magic bullets you cannot guarantee that you will live to be 100 and never get sick but you can reduce your chances you can reduce your vulnerability ility to a wide range of diseases by by paying attention to how to live your life better. And one of the important tools is to use evolutionary theory. Although not in a simplistic way, right? So it’s not like just emulate a hunter gather and just, you know, you know, follow the nonsense of the paleo diet or whatever. That’s not I mean it’s not all nonsense. It’s just partly nonsense. I mean Paleo diet says you should never have legumes. Yeah. No lentils, no chickpeas, no you know I mean what I mean tell me really do you really think people who eat lentils and chickpeas are going to die young? I mean that’s just obvious silliness, right? But but there’s some other good messages from the paleo diet. I mean it’s another story but um um um uh so that evolutionary information if used properly done sensibly paying attention to the complexity and test hypothesis don’t just make simplistic assumptions that can help us like like you said before when you published the first uh uh born to run paper uh you’ve got uh some push back from the status quo people who want to keep it that way perhaps and perhaps this This is the the way it always been with science. It’s not just science. It’s just human nature. Human nature. Yeah. People always um um look, it’s my job as a scientist to be skeptical. When I pick up a paper, it’s my job to say, “How is this wrong?” Right? So that’s their job and they and they need to that’s okay. Um but sometimes it gets a little silly. Um uh I would have to I have to say by by now I would say you know it’s more than uh 20 years since we published that paper actually. um and um um and uh and now I would say actually it’s now become it’s it’s now become part of the status quo but it took you know we published dozens and dozens of papers you know trying to test various components of the hypothesis and slowly slowly um it’s it’s become accepted but it took time but that’s okay that’s that’s the way science works yeah this is the right approach I think okay before I ask the the last question. Uh just one more thing that I I I hate to leave behind. You’ve mentioned a couple of times about longevity but uh the paralytic world you said seven centuries is the seven decades. Seven decades. Yeah, of course. Um how about modern places like you know the studies about Japan and stuff like that. Blue zones. Blue zones. [laughter] Oh, I’m going to get in real serious trouble for this one. Look, I mean, [laughter] Blue Zones is mostly marketing, right? Think about it, right? You got five little V places in the world. One in Costa Rica, some village in Sardinia, Lom Linda in California where the Seventh Day Adventists I live, um Okinawa and some island in Greece, I think it is. Those just those five places those five that’s it are where there’s a a high percentage of centinarians. So the idea is that if you live like them you too are going to live to be 100 years old. Yeah. Romantic idea. So here’s the here’s several problems. The first is even in place those places that out of a 100,000 people maybe you know uh 40 live to be centinarians. So we’re talking 0.04% 04% of the population. Oh, really? Yeah. And I’m sorry, but those are that’s called a statistical outlier. You should not make your decision about how to live your life based on a statistical outlier. That’s like deciding, well, you know, those people don’t get hit by lightning, so that’s how I’m going to live my life, right? That’s not how it works, right? You what you should care about is what the average person in those populations do. Guess So, and Japan has the highest average longevity in the world. Guess guess what country is number two? I have no idea. It’s Switzerland. I can tell you in Switzerland they don’t eat anything like a blue zones diet. They eat tons of cheese and whatever, you know. I mean, you know, they eat lots of meat and they probably, you know, I I don’t know exact Swiss diet, but but look, so so you’re just as well off living like a Swiss person as you are like a Japanese person, right? So it’s a very it’s bad statistics to to to make your decisions based on outliers. you should go based on the mean. Secondly, think about blue zones. If you somebody who’s in a blue zone in in a in a some like this v village, I have never seen a study which compares what they eat and how they live their life with like three villages over where they probably have ex do they have different diets? Do they live their lives differently? I doubt it. Right. Um I’ve never seen the study because we know what the answer of that study would be. So there’s so so you you know it’s just I don’t know. Look, but that said, most of the stuff that the Blue Zones diet suggests is pretty sensible. You know, eat a lot of plants, don’t, you know, get exercise, don’t drink too much, don’t smoke. Um, do you need centinarians to tell you that? I mean, so there’s a lot of marketing because people are out there, everybody wants to live a long life. There’s money to be made and there are lots of people out there trying to figure out how to make money off of this and this is just another way. So, are is the basic evidence [laughter] basic recommendations of the blue zones wrong? No, they’re not. But are they is it because these people in these villages live to be centinarians? No, that’s just that’s And furthermore, there was a paper that was just published that showed that a large percentage of the people in the in the blue zones don’t even have birth certificates and that and that the evidence that’s being used to claim that these people are centinarians is kind of suspect. Oh yeah. But but the thing I found I’ve heard about Okinawa and specifically from the book I think some of the listeners might know it. It’s a eky guy which it says a lot about the way they live other than their diet. The the thing is that they have they have the this but the blue zones diet includes stuff other than than diet. Yeah. Not only the diet they they eat. But again do you who doesn’t already know that? I I think many people from where I come from the the big fantasy is retirement for example and Okinawa is like the the place that where they work till they die the till the last day where well it’s not the fact that they work till they die so they stay physically active until they die. Yeah. Right. I mean you I mean sure retirement can decrease people’s life expectancy but it depends on how you retire. Oh yeah. Yeah. Okay. So uh last question about your future uh what uh does your re research involves in the upcoming future? Um well we’re you know we have a lot to explore in terms of physical activity and diet and its effects on health. So we’re looking at all kinds of um um um factors in my lab. We’re looking at everything from, you know, from heads to toes, literally. Um but uh a lot of the work that we’re doing is is uh focused on on on um on countries that are going through this physical activity transition and also this dietary transition because you know um we have a current we don’t see this but it’s we have a current crisis that’s building around the world because you know in America for example only 25% of Americans have normal weight. Yeah. 75% of Americans are either overweight or obese. The numbers are growing around the world and um and that all those pro that’s causing a wide range of health problems, cancers and diabetes and heart disease and and so on uh arthritis uh we can barely cope with that. what’s going to happen in places like your Rwanda or Kenya or I could you know all kinds of countries what as they go through this transition because they’re getting these diseases increasingly but they have a high infectious disease burden on top of that and they have health care systems that are you know I mean we have a terrible health care system but we still have a pretty large health care system that how are they going to handle this right so we have a a current rapid explosion of chronic diseases causing by lifestyle happening around the world and and and and we can’t wait just to simply treat those diseases uh because we’re not going to be able to. We need to prevent those diseases. And so uh what my lab is really interested in is is from a global health perspective how to confront uh changes in lifestyle, diet and physical activity to to kind of see if what we can do to alert people about this and help them understand it so that we can make better decisions. You you mean per se making the these countries make changes in their lives? Help them make changes so they understand what’s going on, right? Because they need the data, they need the information. I mean, you know, again, a lot of the information we have about weight and health, for example, comes from Americans. So, you know, standard studies are you have overweight Americans, obese Americans, and they exercise. Well, that’s not what’s happening in I’m just picking on Rwanda because we’re working there at the moment. But yeah, that’s not what’s happening in Rwanda. And what’s happening in Rwanda is that people are going the other direction. They’re highly physically active and then they stop being physically active. And it’s not like like a street with two directions and just going back and forth is you know becoming less active and you you know the the most of the research that we have is going is is about what happens in the wrong direction trying to help people who are already physically inactive already obese whatever become more active and what’s really happening in those countries is the opposite. People are going from being very physically active and very thin and eating healthy diets to to the other direction. So we need to understand that transition better. Great. Okay. Thank you so much again for your time. H just one le thing last thing I usually ask the the people that come to to the show. What’s the one thing you think people should take from uh this conversation if you had to choose? You don’t need me to tell you how to live your life better. you know, it’s, you know, there’s a wisdom in in some of the older ways. Um, you know, just a few just a few simple shifts to our lifestyle can have massive massive effects. Um, they’re not magic bullets, but they can have massive effects. So, you know, and and I don’t you don’t even need me to tell you what they are. Thank you so much, professor. It was a pleasure. Pleasure. Thank you so much.