in: Health, Health & Fitness, Podcast

Podcast #793: The New Science of Metabolism and Weight Loss

You hear a lot about metabolism. You probably know it has something to do with weight loss. And even if you don’t go in for those supposed hacks around speeding up your metabolism, you likely figure you can at least increase it by exercising more.

This isn’t actually the case, and my guest will sort through this and other misconceptions around metabolism on today’s show. His name is Dr. Herman Pontzer and he’s a professor of evolutionary anthropology and the author of Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy. We begin our conversation with an overview of how metabolism powers everything your body does from thinking to moving to simply existing, and how it uses the food you eat as the energy needed to fuel these processes. We then get into Herman’s field research which shows that increasing your physical activity doesn’t actually increase the number of calories you burn, but why it’s still hugely important to exercise anyway. He also unpacks whether certain kinds of foods are better for your metabolism, offers his recommendations on how to use diet to lose weight, and answers the common question as to whether it’s true that your metabolism goes down as you age.

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Read the Transcript!

Brett McKay: Brett McKay here, and welcome to another edition of The Art of Manliness podcast. You hear a lot about metabolism, you probably know it has something to do with weight loss, and even if you don’t go in for the supposed hacks around speeding up your metabolism, you likely figure you can at least increase it by exercising more. This isn’t actually the case though, and my guest will sort through this and other misconceptions around metabolism on today’s show. His name is Dr. Herman Pontzer, and he’s a professor of Evolutionary Anthropology and the author of Burn. New research blows the lid off how we really burn calories, lose weight and stay healthy. We begin our conversation with an overview of how metabolism powers everything your body does from thinking, to moving, to simply existing, and how it uses the food you eat as the energy needed to fuel these processes. We then get into Herman’s field research, which shows that increasing your physical activity doesn’t actually increase the number of calories you burn, but why it’s still hugely important to exercise anyway. He also impacts whether certain kinds of foods are better for your metabolism, offers his recommendations on how to use diet to lose weight, and answers the common question as to whether it’s true that your metabolism goes down as you age. After the show’s over, check out our show notes at

Alright, Herman Pontzer, welcome to the show.

Herman Pontzer: Thanks for having me.

Brett McKay: Alright, so your field research has uncovered some counter-intuitive things about our metabolism, and we’re gonna dig into that today. But before we do, I think it would be helpful to do a short metabolism 101 class for our listeners. Because I think people throw around that word metabolism a lot like, “Oh, gotta speed up my metabolism.” But they might not know exactly what that means. So what exactly is metabolism? And then we’ll go from there.

Herman Pontzer: Sure, sure. So yeah, I think you’re right, people don’t always… Aren’t always told the right thing. Your metabolism is all the work that your cells do all day. So you’ve got 37 trillion cells give or take, and each of them is a tiny microscopic factory that’s bringing in raw materials, that’s the nutrients in the foods that we eat, and turning them into various molecules, hormones, that kind of thing, burning them for energy. And all of that work that our cells do, each of those little factories do, that takes energy, and so metabolism is all of that, it’s all the work that’s happening. And since work requires energy, we can think about metabolism either as the work itself, so people do focus on things like how molecules get changed around by cells, it’s called metabolomics, the products that they make. Or you can focus on the energy it takes to do that work, and that’s what most people focus on in metabolism research like me, we measure all the work that our cells are doing by measuring the energy that our bodies burn.

Brett McKay: Gotcha, okay, so metabolism is the measurement of energy our body is using to do what it needs to do: Breathe, heart beating, reproduce, get off the couch…

Herman Pontzer: Yeah.

Brett McKay: That’s metabolism. Okay.

Herman Pontzer: Yeah, that’s right. And most of it, you’re only dimly aware of or not aware of at all. So for example, every nerve cell in your body needs to keep a very precisely amount of negative charge inside of its cell relative to the outside of its cell, or else your nerves don’t work. And so to do that, it’s constantly pumping these ions, these sodium and potassium ions in and out to maintain that balance, maintain that negative charge. Your liver is constantly at work, detoxifying all the stuff you ate, helping break down nutrients. Your spleen, your immune system, all of it, there’s so many things that are happening. Your brain, your brain runs a 5k every day, your brain burns 300 kilo calories of energy everyday, that’s the equivalent of going on a five kilometer run, and none of this you’re aware of, you’re only aware of the very small amount of energy that you spend… Relatively proportionately, that you spend on things like exercise.

Brett McKay: Yeah, so that’s an important point, when people typically think about speeding up their metabolism, and we’ll talk about why that actually isn’t a thing, they think, “Well, I just gotta exercise and move more, and that’s gonna burn more calories.” But you make the point, no, most of the calories you burn, it’s just functioning, just sitting there existing, listening to this podcast.

Herman Pontzer: Exactly, yeah, yeah. Even if all you did is binge listen to The Art of Man podcast, all day, you’d still burn about 70% of the energy that you would have burned in an active day.

Brett McKay: So, okay… So yeah, I think you break it down, there’s a chart, the percentage of our calories that we burn throughout a day that are geared towards just existing, and then there’s movement. And then there’s another one, another criteria of how we burn calories, I think it’s called NEAT? N-E-A-T.

Herman Pontzer: Oh, yeah.

Brett McKay: What is NEAT?

Herman Pontzer: Well, so NEAT is this concept that you’re moving when you’re not paying attention to it, so fidgeting, standing up and walking over to get a cup of coffee, that stuff. It stands for Non-exercise activity thermogenesis. And yeah, it’s a nice acronym for… NEAT is a nice acronym for that, and it’s this idea that not only are you burning energy to move when you’re paying attention to it and exercising, but you’re also burning energy in these other ways as well. But there’s even more than that, because NEAT’s not… Okay, so NEAT was a concept that people developed because they were having a hard time making the numbers add up. When they would try to understand how people are spending their energy, they would look at basal metabolic rate, that’s your energy at rest, like 6:00 in the morning when your body’s super calm and still and you’re in the nadir or you’re in the valley of your energy expenditure for the day. Your organs are as quiet as they’re gonna be, you take basal metabolic rate, you take how much people exercise, you take how much energy it takes to digest food, you add those up and there’s missing calories ’cause people are burning more calories than those three components would suggest.

You add those up, you don’t get the same numbers you get when you really measure it as a real empirical measurement, it being total calories burned over 24 hours. And so people thought, well, there’s this NEAT stuff too, there’s movement when we’re not paying attention, and that’s true, I guess we could add that in it as well. And I would say there’s other things as well that we don’t always pay attention to that we need to think about as well, which is the circadian fluctuations, the circadian rhythm of our energy expenditure, you’re burning more energy in the middle of the day, especially when you’re alert, than you are at night while you’re sleeping. So even without moving, just the act of being alert and awake and at the peak of your circadian metabolic cycle is gonna be burning more energy than at your lowest point. So we can get into the weeds, we can get into the nuanced weeds about how the body spends energy, but you’re right, we can break it down to those components as well.

Brett McKay: But I think the big take away, the majority… Like you said, the majority of our calories burned throughout the day is this BMR, this basal metabolic rate, just… When we’re at rest, thinking, breathing, heart beating, liver producing all the hormones that it does, that’s where most of our energy is geared towards. Okay.

Herman Pontzer: That’s right.

Brett McKay: So let’s talk about how our body takes the food we eat and converts that into energy. So basically, when we consume food, you can categorize the nutrients in that food into three broad categories, they’re called macronutrients. We got protein, carbs and fats. And our body metabolizes these different macronutrients differently. Can you walk us through big picture, and we don’t have to get into the Krebs cycle.

Herman Pontzer: Sure.

Brett McKay: But big picture, what are the difference between how our body takes these different macronutrients and turn them into energy so we can power our bodies?

Herman Pontzer: Yeah, sure. So we can start with carbs. So carbs include starches, they include sugars, and no matter whether it’s a complex carbohydrate, like you get from a potato, or if it’s a simple sugar like you get from the sugar in your coffee, your body and your digestive tract breaks those down into very simple sugars, things like glucose and fructose. Glucose is by far the major simple sugar, so that’s why we talk about blood glucose levels, ’cause that glucose, it’s absorbed into your blood, and then really it only has a couple places to go. It can go and get stored as glycogen, which is kind of a short-term savings account for glucose, ’cause glucose is really just all about energy. It can get turned into fat if your glycogen stores are already full, because glycogen… There’s a limit to how much glycogen your muscles and liver can hold. Or, it can get burned as energy. And so, that’s what it’s gonna eventually end up happening, is it’s gonna get burned as energy. But if you’re not using it right now for energy, the glucose, you can store it as glycogen or fat.

The fat that you eat will also get broken down into fatty acids and those get stored as fat or burned. And then the proteins you eat get turned into tissues, like muscle tissue. You’re constantly cycling through muscle tissue ’cause you break it down during the day and you build it back up at night. And your other tissues need protein as well. We’re kind of protein robots walking around. We need a lot of protein to build our tissues. And then when proteins get degraded, when tissues break down, your body will break those down into amino acids and burn those as well. But the main energy supply for your body is the glucose and the fat, and protein is mostly a building block. And we can get into the weeds there, like you say, we can… For example, there are sugars that help build your DNA, there are fats that help build your cell membrane. So, things get used for different jobs, but those are the three big jobs.

Brett McKay: Gotcha. Okay, and so I think the big takeaway here is you literally are what you eat. When you eat carbs and fats, that stuff’s in proteins, it’s broken down and it’s powering every part of your existence. And the idea is, okay, if you eat this stuff, you… Say you eat a pizza, use it as an example, if you do pizza pizza, your body’s going to process that, break it down. You might use it right away for energy. If it doesn’t need that energy right away, if it’s glucose or carbs, it’s gonna store it as glycogen. If the glycogen stores are too full, well then the body is, “Okay, well, we’re gonna save that energy for later. We’re gonna turn that into fat.” And the same with fat, you eat fat, you either use it right away to power your body. If your body doesn’t need it then, then it will store it as fat around your belly.

Herman Pontzer: That’s right. That’s right.

Brett McKay: That’s basically… Okay. Okay, so now that we have this basic understanding of how metabolism works, let’s get into your research. Because like I said, it’s counterintuitive what you found, ’cause I think a common idea out there that people have is that if you move your body around a lot, you’re gonna burn more calories, than someone who moves less. And that’s exactly why people, when they say, “I’m gonna start losing weight,” what do they do? They sign up for the gym, they start exercising.

Herman Pontzer: Yeah.

Brett McKay: But what you’ve done with your field research as an anthropologist, you went to a group of hunter-gatherers in Africa, called the Hadza, and you measured their daily caloric expenditure. And the Hadza, they’re hunter-gathers, they’re moving around all the time. They have to move to eat, whether they’re gathering tubers or hunting animals out in the wild, they’ve gotta work a lot to get their food. And you figured, well, they probably burn a ton of calories because they’re moving all the time.

Herman Pontzer: Yeah.

Brett McKay: What did your research find?

Herman Pontzer: Yeah, that’s right. So we did this project because humans evolved as hunter-gatherers, so our species is Homo sapiens, so we’re in this genus Homo. The genus Homo is older than us, its 2.5 million years old. And for the last 2.5 million years, the entirety of the genus Homo’s evolution, we’ve been hunting and gathering. And then our species, Homo sapiens, shows up about 300,000 years ago, and we’re just one more hunter-gather group in a hunting and gathering genus. And so if you wanna understand anything about how our bodies evolved or what our bodies are built for, a hunting and gathering community is… That’s the best context you can have. Now, they’re not living in the past, they’re not trapped in amber or anything like that, they’re as modern humans as you and I are. But because they’ve held on culturally to this hunting and gathering lifestyle, it allows you to ask, “How do our bodies work in a hunting and gathering lifestyle?” So it’s one of the best windows you’ll get into how our bodies were shaped for hunting and gathering.

And like you say, they’re incredibly physically active, they worked with us, the group called the Hadza in northern Tanzania. They get more physical activity in a day than most Americans get in a week. And so going into it, we thought, “Well, gosh, we have to understand how many calories they’re burning,” because obviously, it’s gonna be a lot different than you and me. And so we went there. We stayed… The first time I went there, I went for about two months, living with them, measuring energy expenditures over the course of a week, with this isotope tracking technique, which is really good, empirical, objective measurement of calories burned per day, and you get it over about a week-long period. So, it’s a really good look at daily energy expenditure. And yeah, we got back to the States with our samples, ’cause you use urine samples to track this stuff. We had to get them analyzed in a lab down at Baylor. And we got the numbers back and we were shocked, because Hadza men and women were burning the same amount of energy everyday as people in the US and Europe and other industrialized countries. There was no difference. In fact, Hadza men and women are burning less energy every day, fewer calories every day, than men and women in the West. Once you account for body size, they tend to be a bit shorter. So once you account for body size, it’s indistinguishable. You cannot distinguish daily energy expenditures between us and them. It’s really, really remarkable.

Brett McKay: Oh, yeah, just to be… I wanna emphasize this point. They, on average, walk like five miles a day, I think, was like one of the…

Herman Pontzer: Oh, at least, yeah, that’s the women. The men walk further. Yeah, absolutely.

Brett McKay: And a western like me, I don’t… I’m lucky if I get my 10,000 steps in a day.

Herman Pontzer: Yeah, so that’s a fun way to do it. The women get about 13,000 steps a day on average, often with a kid on their back, and men get about 19,000 steps a day on average.

Brett McKay: Alright, so what’s going on there? How is it that they’re able to burn the same amount of calories as us not-so-active Westerners. What’s going on?

Herman Pontzer: Yeah. Yeah, well, that was the big puzzle, and so we’ve been trying to figure that out for the last 10 years. Here’s what we know. We know that there’s nothing magic about the way that they’re moving, right? So we’ve measured the energy cost of their walking. We’ve taken a system out there that allows us to measure the energy cost to walk, and it’s the same as you and me. So there’s nothing special about their muscles, they’re not more efficient that way. Instead, what seems to be happening is, the energy that they spend on activity is being rather than adding on top of everything else and creating a higher total energy expenditure per day, the energy they’re spending on all that activity is taken away from other expenditures. So basically, they’re reducing other expenditure and other aspects of their bodies to make room for this really large amount of energy spent on daily physical activity.

Brett McKay: Wait, and where do you… Have you been able to see where the body’s taking away… What’s going on? Where’s the body reducing caloric expenditure, so they can take into account that extra activity?

Herman Pontzer: Yeah, so this has been the focus of research over the last few years. Here’s what we know, and part of this is based on what we know from groups like the Hadza, and part of this is what we know from other people, like for example, athletes in the US and elsewhere who are also really physically active, and then sometimes are easier to study, because we can get them into labs here. Here’s what we know. When you’re really physically active, you have lower levels of baseline inflammation, so things like C-reactive protein and the other stuff that is your immune system kind of over-reacting all the time, there’s high levels of inflammation that Westerners tend to have, it’s lower in people who are really physically active. So, that’s your immune system basically dialing it back, spending less energy, if you’re really physically active.

Reproductive hormones, testosterone levels, estrogen levels in men and women respectively, are lower in groups like the Hadza and in athletes as well, endurance athletes as well. If you are a Hadza man, or a Hadza woman, your reproductive hormone levels are gonna be… 20% lower, 30% lower than an adult your age. There’s an age effect, of course, as well with your reproductive hormones, so we’re accounting for age with that. That’s your reproductive system spending a little bit less energy on keeping itself up, and that’s gonna save energy. Now, that doesn’t mean… I wanna be really clear, that doesn’t mean there’s fertility issues, or anything like that, or that they’re any less manly, the men, because they have slightly lower testosterone levels, nothing like that, but just the reproductive system is just taking a little bit less energy per day in really physically active folks.

And then the other big thing, and we don’t have measurements of this with the Hadza, but we do with other physically active groups and with athletes, stress levels and stress reaction, stress reactivity, right? So if I stress you out, I accost you on the street and give your heart a bump, and your epinephrine levels go up, your adrenaline levels go up, your cortisol levels go up, or if I do that in the lab and I make you do mathematics in public, that’s a really fun way to get people to get stressed out, your heart rate will go up, your cortisol levels go up. But if you’re an athlete, or if… We think if you’re someone like the Hadza who’s physically active all the time, that reaction will be not as sharp, not as big, and will… You’ll go back to baseline faster, you’ll spend less energy on that stress reaction than if you are a sedentary person who doesn’t exercise a lot. So these are all the different various ways, we think, that the body’s able to take energy away from other tasks in ways that actually are really healthy for us, we can talk about that too, and make room for more physical activity.

Brett McKay: I guess to help people understand this, why it’s going on, basically our body’s regulation system for metabolism, it’s all geared towards surviving and reproduction, right? And so yeah, it makes sense, like you talk about the reproductive hormones going down. Well, if you’re facing extreme physical activity, extreme caloric expenditures just to survive, to get food, your body’s like, “Well, we’re gonna prioritize survival over reproduction a bit more, so we’re gonna adjust things.” So I guess people understand that, your body’s metabolizing energy either to survive and reproduce, it’s going to modify things to further those goals. And I guess survival’s the first goal, and then reproduction is number two.

Herman Pontzer: Well, yeah, I mean, it depends. In some species that are short-lived, it’s all about reproduction. They’ll throw away the survival piece. Humans, because we’re long-lived, we’re evolved to be here for the long term and to get through the tough times. Yeah, that’s right, well, in a bad time, we’ll focus more on the survival piece, our bodies will. But yet, we see this kind of a reproductive issue, reproductive effects in the Hadza, so a woman in a Hadza community, they like big families, they don’t use contraception typically, but a woman will still have a kid every… Between two and three years. So that’s without any contraception. In the West, women who have a kid this year, even if that woman decides to breastfeed and is… Yeah, so she’s nursing, if she doesn’t use contraception, is likely to be pregnant again within a year. So it’s much… The reproductive system is actually kind of, it’s dialed back a little bit in these really physically active groups. And by the way, that’s probably more healthy that most guidelines for things like pregnancy say, “You should put more time between pregnancies.” So that’s one… It’s a good thing. But you can see the impact of how the energy’s being spent.

Brett McKay: And so what you guys have found, what you researchers found, is that our bodies, all human bodies, have this sort of constrained daily expenditures. It’s like the… There’s a range, upper limit range of how many calorie you can burn through a day.

Herman Pontzer: Yeah, that’s right. So it’s not just the Hadza. I want to be clear about that. We’ve done… If you’re a scientist and you find this really interesting result, the first thing you assume is that you’re wrong, so you go to all the… You’ve done all the work to try to make sure that that’s a really strong… A good result for the Hadza and it is. You can use different techniques, different approaches, you get the same answer. So Hadza data are solid, and then you wanna replicate it. You wanna make sure it’s not just one society where you’re seeing this or even one species, and so we’ve seen this in other human groups, now. We’ve looked at other farming and hunter-gatherer groups and mixed groups, you see the same thing. Same daily energy expenditures as Westerners, industrialized communities, even though they’re much more physically active. We see this across species.

So we’ve done this study where we looked at different species of primates, monkeys and apes, and lemurs and lorises. In the monkeys in a zoo, from the same number of calories every day as monkeys in the wild. You can do this in a laboratory setting. You can get mice, you can take out their running wheel away from them for a while and then give it back, and they’re less active and then they’re more active, and you don’t see any effect on their daily energy expenditure. So this is a really robust thing. Our bodies… And probably all mammal species, maybe even birds species too, seem to be built to really try to regulate how many calories we’re burning everyday.

Brett McKay: So in humans, what’s the constrained daily expenditure? What’s the range?

Herman Pontzer: Well, it’s gonna be a function of your body size. Bigger people expend more energy than small people, but women burn about 2400 kilocalories a day. I’m saying kilocalories, cause we always say calories, it’s actually not correct, but you can just replace that with capital C, big calories if you want to, but women burn about 2400 kilocalories a day, men burn about 3000 kilocalories in a day. That can vary a little bit, again, with your body size, that’s the biggest factor, but lifestyle has a really small effect on it.

Brett McKay: Alright, so this is a cross. About 3000 calories, whether you’re a Hadza or some guy in New York, your body’s probably burning about three… This is total, so this includes… This is like BMR, so that resting, basal metabolic rate, on like your activity.

Herman Pontzer: Yep, it includes that, it includes the energy to digest your food, it includes whatever exercise you did, it includes taking that walk to go get a coffee, it includes the stress reaction from your boss throwing extra work at you at 5 o’clock, all that stuff.

Brett McKay: Okay, so the implication of this finding is that relying solely on exercise to lose weight is probably not an effective strategy because your body… ‘Cause you exercise to burn more calories than you’re consuming, but you’re… We’ve discovered our body’s gonna figure out a way to compensate for the increased physical activity so that you stay inside your constrained daily expenditure.

Herman Pontzer: Yeah, there’s two reasons that exercise end up being a poor tool for weight loss. One, is what we’ve been talking about, your body will adjust and you’re adding… You think you’re adding 300 kilocalories a day to your daily routine of exercise, but you’re not really because that 300 kilocalories of exercise is at least partially being eaten up by adjustments other places. The other thing is that even if you are able to manage to pump your energy expenditure up a bit with exercise, especially in the short term, ’cause it takes a while for the body to adjust, you’re gonna eat those gains, ’cause your body is also… Part of the system as your body is very well evolved to match energy intake with energy expenditure, and that also happens below our conscious thoughts. So if you are able to increase your metabolic rate by a bit, you’re just gonna eat those gains and you’re gonna end up right back where you are, where your energy intake matches your energy expenditure and you’re not changing your weight at all.

Brett McKay: Alright, so I’m sure people are listening to this and is like, “Well this is depressing.” But we’re gonna talk about why actually this is so important. We’re gonna take a a quick break for a word from our sponsors.

And now back to the show. Okay, so people might hear this and go, “Okay, if I wanna lose weight, then exercise doesn’t do anything for me, what I need to do is reduce the number of calories I take in by a lot to lose weight.” But that doesn’t work either, and can even backfire sometimes, so what happens when we significantly reduce our caloric intake?

Herman Pontzer: Yeah, if you go on a crash diet, really cut the calories in half kind of thing, then this is another evolved survival response, your body says, “Oh my gosh, we’re starving, there’s no food in the world, and we gotta get through this lean period.” And so what it’ll do is, without your being aware of it, it will reduce your metabolic rate. So all those systems that you’re not aware of, your body can take the foot off the gas and spend less energy on those, and all of a sudden you aren’t burning as many calories as you were before. And not only do you feel miserable because you’re starving yourself, but you’re actually… Your body is actually trying to frustrate those weight loss attempts… Weight loss effort because it is reducing the energy expenditure that you had before, so it’s actually that difference between the energy you’re taking in and the energy you’re burning gets smaller because your body is saying, “Oh my gosh, we’re starving, turn the energy down.”

Brett McKay: And then so we’ve seen this with Biggest Losers contestants. They go… They’re losing hundreds… Like 150 to… Like a human, they lose a human off of their body, a full-grown human. And then you do the follow… How do they do afterwards? And I think most of them gain the weight back.

Herman Pontzer: They almost all do, and that’s really… It’s sad because of how much effort that you know they put into it and how much it meant to them, but it’s also kind of predictable because your body doesn’t wanna change weight. There have been vertebrates, part of the group of animals called vertebrates, we’ve been around for half a billion years, and for almost all that time, probably all of it, losing weight’s been a really bad thing. You’re losing weight, you’re on your way to dying, and so there are all these involved mechanisms not to lose weight, which is why it’s actually the most important that you can do for your health is to try to not get overweight in the first place. And that gets us into discussions about how we think about how we take care of our kids and how we take care of ourselves, especially in our early years, but yeah, it’s really hard to change once you do… Once you’re overweight. The best thing you can do is, if you’re looking at behavioral strategies, is to try to change your diet, but like you say, if you go too fast, too hard and too fast, too soon, then that can backfire because your body responds to that by, again, reducing energy expenditure and frustrating that weight loss.

Brett McKay: Alright, so yeah, the metabolism, you can’t outsmart the metabolism, there’s no… It’s gonna figure things out.

Herman Pontzer: Yeah, one of the biggest frustrations I have when I look at online self-help, “Here’s how you’re gonna take charge of your metabolism and boost your metabolism or whatever.” All of this stuff, it all makes people think that they’re in charge of their metabolism. Right? Which is completely not the case. Your metabolism is working behind the scenes. It’s smarter than you. And it adjusts to you. You can’t really push it around. In a way it’ll manipulate things behind the scenes in ways that are gonna frustrate what you’re trying to do. Now, and I hope we’re gonna talk about this, you should still exercise, absolutely, and if you do wanna try to lose weight with diet there’s some strategies you can take, but I think this idea that we’re in the driver’s seat, revving our engines, our metabolic engines in a sort of really simplistic way. And that’s how we burn calories. I wish we could move away from that. ‘Cause it’s just not the science.

Brett McKay: Right. So you can’t speed up your metabolism, like that’s…

Herman Pontzer: No. It’s really hard to do, and basically, yeah, you can’t do it.

Brett McKay: Okay. So let’s talk about this. So while exercise can’t be the sole driver of weight loss, you make it very clear. You devote a whole chapter of this. Like that doesn’t mean you shouldn’t exercise and you actually make the case that because of humans unique metabolism, maybe we can talk about how it differs from the apes, because of our unique metabolism we actually it’s really, really important for us to move a lot. Why is that?

Herman Pontzer: Yeah. Well, so like I said, we’ve been evolving as hunter gatherers for two and a half million years and hunting and gathering takes a lot of work. And so our bodies are actually evolved to expect and require a lot of physical activity every day. It’s what our organ… As evolved organism, it’s what we’re evolved to do. And if we don’t do it, we get sick. And so, yeah. Getting all those steps every day is really important. And apes are lazy, right? I mean, I’ve done field work with apes. I’ve worked with apes in zoos. They’re impressively lazy, getting 5,000 steps a day maybe, is kind of a typical day for an ape. Even if you count up the climbing and all that stuff. And they’re just fine like that. They don’t get sick from being like that. In fact, a chimpanzee in a zoo probably has less than 10% body fat. That’s a typical, that’d be typical for a chimpanzee in a zoo, even though they’re just sitting around. And so we can’t do that. If we act on our ape-like impulses just to be lazy all day, yeah, we get real sick.

Brett McKay: Yeah. That was really interesting to me is that apes in captivity don’t really get fat, like when they eat more food instead of turning that into body fat, apes just turn that into lean tissue.

Herman Pontzer: Yeah. Isn’t that crazy. Humans are… It’s another evolved piece of our physiology. We are evolved to put on fat really easily. And it probably goes hand in hand with having a faster metabolism. So we’ve actually evolved a faster metabolism than apes have that allows us to have things like these big brains that we are so energetically expensive, and we have big fat babies more, and we have them more often than apes do that, takes a lot of energy. We are physically more active than apes. So all of this is like we’re a high energy ape. And as a kind of a backup plan, we’ve also evolved this propensity to put on fat because if you’re always burning a high level of energy, given a high metabolic rate that you can’t kind of turn down, you can’t adjust much at all as we’ve been talking about, you need to have a backup in case you have periods where there’s not much food and that’s where our body pack comes in.

Brett McKay: Right. So, yeah, I get… Okay, just to make sure I’m getting this right. So apes, they don’t have to move around a lot to get their food. So they have a slow metabolism and there’d be you no reason for them to put on body fat really, because they would never… They would probably wouldn’t be long periods of time where they wouldn’t go without food. Like, well, I’ll just grab this leaf here. Humans, we had to hunter and gather to gather foods that requires a lot of energy. And so we have to… If there’s instances where we don’t have a lot of food available, our bodies are like, Well, we need to have… We need to store body fat in case that ever happens so that we have the energy to walk and find tubers and gazelle again.

Herman Pontzer: Yeah. And reproduce and do all those things that were built to do. Absolutely.

Brett McKay: Okay. So we have to move a lot. So our body uses a lot of energy. You also highlight research that exercise while isn’t useful to lose weight, it’s really important in maintaining weight loss. What’s going on there?

Herman Pontzer: Yeah. That’s a really interesting piece of this. So if you go on an exercise program tomorrow, yeah, you might lose a couple pounds over the course of the year, but that’s not the big benefit of it. Big benefit is how it kind of makes a lot of our systems more healthy. And if you’re able to lose the weight with usually with diet as the big intervention, that exercise helps you keep it off. And we don’t entirely know why. What we think is happening is that the exercise, the… When you exercise your muscles send all these signals to your body, all these hormones and all these things. So your body knows you’re exercising, it affects every part of your body. And one of the things we think it helps do is regulate how hungry and how full we feel. So how much we eat. And so kind of exercise has this effect of keeping our hunger and fullness better regulated. So we don’t overeat once we’ve lost the weight. If you exercise, it helps you keep at that weight and not overeat and gain all that weight back.

Brett McKay: Okay. So, yeah, I think when people… Okay, I wanna… There’s some interesting things going on here, because our metabolism again is weird, when we exercise more, we’re gonna eat more because we need more energy, right? But if, I think what you’re saying here is that when you exercise, there’s a better connection between the calories you need and your hunger levels, right? So it’s like…

Herman Pontzer: Yeah, that’s right, yeah, that’s right, And once you’ve lost the weight, the energy that you need is actually less, right? Because you’ve lost all that weight. And so if your body was just trying to match how much you need and how much you’re taking in, you’ll match that at that lower level and maintain the weight better. That’s what we think is going on. It’s actually not entirely well understood why exercise is such a good tool for keeping weight off. But it absolutely is that’s what all the data show.

Brett McKay: Okay. So overall, exercise is gonna help you lose a little weight, but it’s really useful in helping you keep the weight off and maintaining your weight loss. And it’s probably because it helps match your appetite to your actual caloric needs and it’s helping control those hunger signals, and something that’s interesting with this research is that they found that sedentary people, people who don’t move hardly at all they actually eat more than those who are active, and it’s probably because their bodies have somehow become out of touch with how much food they actually need. And then something else we talk about Biggest Loser contestants, something else that’s interesting with the research there is that with all the contestants, their metabolism dropped after the show, and then it stayed low long-term, but among those who exercised, even though their metabolisms were low as well, they actually did the best in keeping the weight off. And again, it’s probably because of the way exercise regulates appetite. So, yeah, exercise plays a big role in weight maintenance.

Herman Pontzer: The other thing that it’s doing, all of the other adjustments it’s doing, keeping your inflammation levels down, reproductive hormones in a healthier place, your stress reactivity down, that is gonna add years to your life. Those are all ways to avoid heart disease, avoid diabetes, the things that we’re most likely to die from, is by exercising. So, thinking about exercise as a weight loss tool, still kinda misses the point. It’s actually really good for all this other stuff that’s gonna keep you healthy and active and add not just years to your life, but like healthy good vital years to your life.

Brett McKay: Well, let’s talk about diet, because I think that’s the way we can lose weight, just reducing calorie intake. But then there’s people who have created diets based on how our body metabolizes different macronutrients, and I think the most popular one is like a low carb high fat diet.

Herman Pontzer: Yep.

Brett McKay: And I think the big idea is Gary Taubes’s idea is like, well, the reason why you get fat is insulin, and when you eat carbs, insulin level spike and it drives the storage of carbs or fat as body fat. And so you cut the carbs, you reduce the insulin, you’re gonna lose weight. What does your research reveal about diet and weight loss based on a macro nutrient?

Herman Pontzer: Yeah, the carb idea, it’s a beautiful idea. It just doesn’t fit the evidence, unfortunately. So first of all, we can say, a group like the Hadza, and there are lots of them still that are farming and hunting and gathering and doing that kind of stuff. They eat a lot of carbs, in fact, they eat more carbs as part of their diet than people in the US do. So if it were all about carbs, then folks like the Hadza should be incredibly obese, but of course they’re not. They’re but healthy weight throughout their whole lives, and they don’t ever gain weight in their middle and older age, they’re just fine. And so if it’s really just about carbs then groups that eat a lot of carbs ought to be overweight, they’re not. Secondly, when you do the control laboratory studies and you put people on low carb diets versus on low fat diets, you don’t see any difference in weight loss outcomes. And in fact, depending on the size sometimes you see people do a little bit better on low fat, but that’s… The main outcome is that you just don’t see any difference at all.

If you cut calories by cutting carbs, or you cut the calories by cutting fat, you get the same outcomes. And the third is, if you do a study where you take people and you randomly assign them to a high carb diet or sorry to a low fat diet or a low-carb diet, this has been done a few times now. There’s no difference in outcomes. People, again, lose weight just as easily, just as well on low fat as they do on low-carb diets, and so there’s just really no… The carbohydrate insulin model of obesity, which is the Gary Taubes’s idea, it’s been tested in a lot of different ways, and it’s a beautiful idea, it’s very elegant, it just doesn’t work. It doesn’t fit the data. Now, low-carb diets work for a lot of people, that’s a different question. The question is, why are they working? And how do they work? And the answer is, they basically, you’re cutting calories but that doesn’t mean that the mechanism that’s been proposed as insulin-based mechanism is really what it’s all about, ’cause that just doesn’t bear out.

Brett McKay: Alright, so again, you can’t trick your body, your metabolism?

Herman Pontzer: Well, I mean, no, I think this is a different thing about tricking. So, okay, the counter argument from the folks like Gary Taubes would be like, “Oh well, you’re saying all calories are the same, you’re saying, it doesn’t matter what you eat. Is that what you’re saying?” You know, and the answer is “Well, no, no, we’re not saying the 100 kilo calories of broccoli is gonna affect us differently and feel different than 100 kilo calories of potato chips.” So, in both those cases, those are very carb-heavy foods. And so the kinds of food you eat matter, but all the evidence says that the way that you feel full on fewer calories, which is really the goal to lose weight with diet, is that we have to think about the way that those calories affect our brains.

So we talked about how your brain is really well adapted to match the calories in and the calories out, to match our fullness and hunger to our weight. The way that you kind of push that system to lose weight without feeling miserable is to find foods that make you feel full on fewer calories, so things like higher fiber foods can help, higher protein foods can help. That’s where low carb diets come in, by the way, you take a whole macro-nutrient group out and you give yourself foods that really have a lot of protein in them, and you feel better. You feel full on fewer calories, that’s why low calories work for some people. Yeah, so I mean, that’s what we’re talking about here. So we’re not saying that there’s no… That foods don’t have different effects, that kind of stuff, of course they do. But do all diets work through the insulin pathway or do they work through manipulating the way our bodies feel, our brains feel that seems to be the more likely mechanism.

Brett McKay: Yeah, we had Steven Guinea on the podcast a while back ago. And he talked about this, right, how our brain… How it feels about our food that we’re eating, and one of the interesting takeaways I got from him was, one thing you can do is just eat less palatable food, ’cause palatable food you just wanna eat a lot of it. We’re talking about Doritos and cheese burgers it’s like oh I just wanna keep… But it’s like if you look at the diet of the Hadza it’s the most boring thing. There’s no spices, it’s just like, well, you’re gonna a tuber it’s kind of burnt, and like some zebra.

Herman Pontzer: Yeah.

Brett McKay: That’s just gross, and so it’s usually like well, “I’ll eat enough to get the energy I need to do what I have to do, but I’m not gonna… ” So one take away, it’s just like eat… Instead of eating a potato chip, eat a baked potato.

Herman Pontzer: Yeah, that’s right, there’s actually a great set of, most of it is anecdotal ’cause nobody… No real nutritionists would ever recommend this diet and I’m not to be clear, but there’s a great anecdotal evidence of people who just eat potatoes and lose lots of weight that weigh hundreds of pounds sometimes, because if all you eat is potatoes, guess what, you are sick of potatoes [laughter] well before you have over-eaten your calories that day, and so that’s one way to do it for sure. And I think that’s what low carb is doing as well, you take a whole class of foods off the menu and how much steak can you eat? How much spinach can you eat? You’re just gonna feel full before you over-consume and that’s the great way to go, for some people that works really well. But it’s not the only way to go and it’s not because of this kind of carbohydrate-insulin magic, I think it’s much more about our brains than that.

Brett McKay: So I think another common idea people have about metabolism… It’s okay, that’s great… We kind of debunked a lot of things, exercise isn’t gonna do much for you to lose weight, basing a diet on a macronutrient probably is not gonna do anything for you.

Herman Pontzer: Right.

Brett McKay: I think another popular idea people have about metabolism is that as you get older, it slows down, that’s why…

Herman Pontzer: Oh, yeah.

Brett McKay: People in their 50 or 60 got the belly… Is that true? Does their metabolism slow down?

Herman Pontzer: You know man, I’m in my 40s and I was really sure that one was true. And then we just recently did this big study, we took measurements from 6400 and some people, and those are people from… People who have just been born, 8 days old, up to folks who are in their 90s. And what we did is we were able to use that big, big data set to measure how many calories people burn over the course of a day and ask how that changes over a lifespan. What we found was that your metabolism is really steady and stable between about 20 years old and about 60, and so there’s no slow down in your 30s and 40s that we were able to detect at all, yeah, that turned out to be another one of these myths. So that’s not to say that it feels the same to be 44 as it does to be 24, I can attest to that. But it’s not metabolism, it’s not the energy burning that’s changing, it’s something else, it’s about stress levels or hormone levels, that kind of thing.

Brett McKay: But it does start slowing down after 60?

Herman Pontzer: At 60, yeah, and that’s really interesting because 60 is also that inflection player, people start to… People get in their 60s, 70s, 80s, that’s when you see your risk of different diseases pick up, heart disease, Alzheimer’s disease, other… Diseases that we associate with aging, those are when those really start to kick in, is after 60, and we’re seeing your metabolic rate decline too. What does that mean? That your cells are slowing down, that’s where your metabolic rate… Which we started off by talking about what metabolism is, it’s all your cells at work, when we see that metabolism is starting to slow down, well that’s telling us our cells are doing less work. And man, we would love to know exactly what’s happening there, what’s changing that it is either promoting or just signaling and telling us about these changes and how our cells work that seem to be related to the disease risk that we see picking up there. Because maybe, maybe we could find a way to keep ourselves burning more energy keep them at a younger state, maybe that would be protective against disease, I don’t know. But it’s… Something we need to look into next, is figuring out exactly why that decline happens and is that telling us about healthy aging, I suspect it is, but we’re gonna have to have more work to figure that out.

Brett McKay: Well, one idea that crossed my mind when you told me that at 60, it starts going down, that would make sense if we understand that metabolism is about survival and reproduction. If you’re over 60, especially for women, reproduction’s off the table, your body doesn’t need calories for reproduction.

Herman Pontzer: Yeah, so that’s interesting, right? Because menopause typically happens when women are in their 40s, late 40s, so actually from an evolutionary perspective, that last 15 years, if you go to 60, let’s say… That’s kind of hard to explain. And what that seems to be about is that the elders in our communities… And this is true in the Hadza, and this is also true here in the States, and it’s true historically and across cultures. Folks who are in their later middle age are doing a lot of work and helping out their own kids and helping out the next generation, and that seems to be really important, so we have this evolved strategy to share and to help, it’s one thing you cannot escape when you go in to work with the Hadza, they’re always sharing, they’re always helping each other out. And it’s not just being nice, it is baked in to being a human, and I love that about the doors that this kind of metabolism work opened up, I’d be like, “Oh my gosh, hunting and gathering.” Right? It’s not just one or the other, you have to do it together.

And that comes out every celebration you ever had, I bet, involves hanging out with other people and sharing stuff, sharing food, sharing birthday cake. Alright, that’s what’s been so hard about all the social distancing with COVID is we’re built to be social and together and sharing. Anyway, so getting up to 60 actually gets you past your reproductive years, for most of us, and that makes sense because again, it’s really… We need to work together. Maybe at 60 is around the time that most folks in the hunting and gathering communities, mortality rates kick in at a higher rate there, and maybe that’s what we’re evolved to get to at least 60, and then the rest of that time you’re in the bonus if you’re in a hunting and gathering group, that would fit the mortality data alright, so that’s an interesting idea. But I do think it’s clearly, is an evolved piece of our physiology, it’s not something we decide to do is just slow down at 60, it’s our cells are built to start doing that.

Brett McKay: Alright, so what’s a person supposed to do with this information? Alright, someone’s listening to this, thinking, “Well, I need to lose some weight.” How should this research guide their approach to losing weight?

Herman Pontzer: Yeah, well, I think that… A couple of things, you gotta start thinking about diet and exercise, as two different tools, two different jobs. Diet is your best tool for weight loss, exercise is your best tool for staying healthy, especially as you age, and there’s some crossover there, but those are the main strengths of those two approaches. For diet, if you wanna lose weight, focus on foods that make you feel full with fewer calories. And so we know what that looks like. I’m not… I don’t study diet per se, but lots of people do. And if you look at that literature, people like Kevin Hall have shown, stay away from processed foods, the ultra-processed foods, the Doritos, right? The sugary beverages, not because of a carb or a fat or whatever, but just think, the whole package is built, literally built, engineered to make you overeat, right? They want you to over-consume. So, whole foods, if you can do it and foods that are high in fiber or high in protein tend to make you feel full, on less.

And the other thing I hear a lot about from people who are dieticians and work with people with obesity, is try to find the parts of your day that you’re eating and you’re not even hungry, right? I mean, I know that, for example, when I get home from work, I get the kids in bed and I finally have a little bit of time to breathe, I’ll tell you what I do, I sit down on the couch, catch up on work emails or watch TV or something like that, read a book and I have a beer. Now, I don’t need that beer and if I was trying to lose weight, that’d be one of the first places I’d go, is I would cut that beer out, ’cause I’m not hungry, I’m not even thirsty, if I was thirsty I could have some water, right, you know what I mean? But that’s just calories that I’m just doing out of habit, that don’t have any nutritional impact on me at all, other than the calories. So that’s the focus you gotta take if you wanna lose weight.

Brett McKay: And no extreme calorie cutting ’cause that’ll just…

Herman Pontzer: No, I think that’s a mistake, I think cutting your calorie intake by a half, for example, or even by a third, yeah, you’ll see some effects faster, I suppose maybe, but you’ll also really mess up your… Your metabolism will slow down, your body will freak out, go into starvation mode, reduce your expenditure and it’s no way to go. It’s also unsustainable, you will feel hungry, you’ll feel miserable and those feelings will win out and you’ll go back to your old ways, you’ll think, “Oh gosh, it didn’t work.” Well, it didn’t work in part because it wasn’t sustainable to begin with.

Brett McKay: Well, Herman this has been a great conversation. Is there someplace people can go to learn more about the book and your work?

Herman Pontzer: Well, yeah, I hope they’ll check out the book, you can get that anywhere you buy books, your local bookstore or places like Amazon. You can check us out here at Duke university, we’ve got a website here for the lab, you can find out what research we’re into right now. And I’m on Twitter, I’m on social media generally, but Twitter’s where I’m most active, @HermanPontzer.

Brett McKay: Fantastic. Well Herman Pontzer, thanks for your time, it’s been a pleasure.

Herman Pontzer: Thank you. It was really fun.

Brett McKay: My guest here was Dr. Herman Pontzer, he’s the author of the book, Burn, it’s available on and bookstores everywhere. You can find more information about his work at our show notes at, where you can find links to resources, where we delve deeper into this topic.

Well, that wraps up another edition of the AOM podcast. Make sure to check out our website at, where you can find our podcast archives, as well as thousands of articles written over the years, about pretty much anything you think of. And if you’d like to enjoy ad-free episodes of the AOM podcast you can do so on Stitcher Premium, head over to, sign up, use code “manliness” at checkout for a free month trial. Once you’re signed up, download the Stitcher app on Android iOS and you can start enjoying ad-free episodes of the AOM podcast. And if you haven’t done so already, I’d appreciate it if you take one minute to give us a review an Apple podcast or Stitcher, it helps out a lot. And if you’ve done that already, thank you. Please consider sharing the show with a friend or family member who you think will get something out of it. As always, thanks for the continued support. Until next time, this is Brett McKay, reminding all listening to AOM podcast, put what you’ve heard into action.

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