Why you can't exercise your way to weight loss
Exercise is essential for your health—but it's a surprisingly poor tool for losing weight. Evolutionary anthropologist Dr. Herman Pontzer explains why your body quietly undermines the math.
Most of us have done some version of the calculation: cut some calories here, add some exercise there, and the pounds will follow. It's intuitive, it's tidy, and according to Dr. Herman Pontzer, it's largely wrong—at least the exercise half of it.
Pontzer is an evolutionary anthropologist at Duke University and author of Burn, a book about the science of human metabolism. His research with the Hadza, a hunter-gatherer community in Tanzania, helped upend decades of conventional thinking about how physical activity affects the calories we burn. The short version: your body is much smarter than the simple math suggests, and it will quietly adjust to keep your total energy output within a constrained range—no matter how hard you work out.
That doesn't mean exercise is futile. It means we've been assigning it the wrong job.
Here are five key insights from a recent Whole New Level episode with Pontzer on how your body actually manages energy—and what that means for weight management.
1. Your body runs on a budget, not a simple ledger
The intuitive model of exercise and weight loss—what Pontzer calls the "additive model"—goes like this: if you currently burn 2,500 calories a day and you add a 300-calorie workout to your routine, you should start burning 2,800 calories a day. Simple addition. The scale should follow.
What Pontzer's research found is that this isn't really how it works. When you take up a new exercise habit, the math does hold up—for a few weeks, while your body is adjusting. But check back a few months later, and you won't be burning 2,800 calories. You might be burning 2,600. You might still be at 2,500.
"Your body has adjusted to kind of make room for that new exercise you're doing," Pontzer explains, "and it doesn't show up anymore in the total calories a day that you're burning."
This is the constrained energy model: your body defends a ceiling on total daily energy expenditure, and when you push physical activity up, it finds ways to pull other expenditures down. The exercise itself burns calories—but the net effect on your total daily burn is substantially less than expected. In some people, it's nearly zero.
2. Most of your calorie burn is invisible to you
Part of why this surprises people is that we dramatically overestimate how much of our energy goes to exercise. When we think about "burning calories," we tend to think about the gym, the run, the workout class. But structured exercise is actually a small slice of the pie.
The typical American woman burns around 2,400 calories a day; the typical man, about 3,000. Over half of those calories—in both cases—go to basal metabolism: your organs doing their jobs quietly in the background. Your brain alone burns roughly 300 calories a day, regardless of how hard you're thinking. Your kidneys, your immune system, your heart—all running continuously, all drawing from the same budget.
Digestion accounts for another 10% of daily expenditure. Being awake and alert costs energy. Even low-grade stress and cognitive load contribute to the burn.
By the time you add up all the invisible work your body does around the clock, physical activity—and especially structured exercise—is a comparatively modest line item. "Unless you're an Olympic athlete," Pontzer notes, "structured exercise is a really tiny part of your daily energy expenditure."
Understanding this makes the constrained energy model less surprising. If most of your burn is coming from internal systems, then your body has a lot of levers to pull when it wants to compensate for extra activity—and you won't feel most of them.
3. Think of your body as a business, not a machine
The additive model treats your body like a simple machine: put in more activity, get out more calorie burn. But Pontzer offers a more accurate analogy: your body is more like a corporation.
It has dozens of departments—immune system, nervous system, reproductive system, kidneys, digestive tract—all drawing from a shared budget (the calories you eat). When resources are flush, every department gets funded. When the budget gets tight—whether because you're eating less or spending a lot more on exercise—the company has to make decisions about where to cut.
These decisions aren't random. They're the product of millions of years of evolution optimizing for survival and reproduction. The brain, for instance, almost never gets defunded—it's too important. But reproduction, immune response, and stress hormones are more flexible. Research shows that people who exercise heavily tend to have lower levels of inflammation (a marker of immune activity), reduced sex hormone levels, and a blunted cortisol response. These aren't failures of health; they're your body's way of balancing the books.
"When resources are limited," Pontzer explains, "your body has evolved to make really smart decisions." Spending more on physical activity means other departments adjust to that new normal.
4. Losing weight changes your metabolism—and not in ways you control
There's another layer of metabolic adaptation that operates independently of exercise: when you lose weight, your body responds by burning fewer calories.
This is well-documented in cases of aggressive dieting. The famous Minnesota Starvation Study and the follow-up research on Biggest Loser contestants both showed that significant weight loss causes basal metabolic rate (BMR) to fall—sometimes dramatically. The body interprets rapid weight loss as a crisis, reduces expenditure wherever it can, and (in some cases) overshoots when the weight comes back, adding extra fat mass as a buffer against future scarcity.
Pontzer is careful to note that this isn't inevitable. Slower, more moderate weight loss may not trigger the same alarm response. But the key insight is that BMR isn't a fixed number you control—it responds to what's happening to your body weight. "BMR and daily energy expenditure don't dictate weight change," as Pontzer puts it; "they respond to weight change."
This is why the path to sustainable weight management can't rely on out-running or out-exercising your body's compensation mechanisms. It has to work with them.
5. Diet is the tool for weight; exercise is the tool for everything else
None of this means you shouldn't exercise. Pontzer is emphatic on that point: the evidence for exercise's benefits is broad and robust—cardiovascular health, cognitive function, mood, longevity, reduced inflammation, better sleep. These benefits are real, and they're significant.
What the research suggests is simply that exercise and diet are different tools with different jobs. "Exercise does everything—or at least helps everything—except weight," Pontzer says. "Weight is much more the job of your diet."
On the diet side, the central question for weight management isn't which macronutrient ratio is optimal or which named diet is scientifically superior. It's simpler than that: how do you feel full on fewer calories? Higher-protein and higher-fiber diets tend to help, because both promote satiety. Cutting ultraprocessed foods—engineered specifically to override fullness signals—is another lever with good evidence behind it. Approaches that meaningfully limit the variety of foods available (low-carb, vegan, elimination diets) can also work, because the body hits its satiety ceiling faster when it has fewer flavor options to cycle through.
The best diet, Pontzer says, is whichever one you can actually stick to. "If you don't like it, you're not going to do it. The percentage of people in this world who will stick with something they find miserable is vanishingly small." That's not a cop-out; it's a recognition that individual variation is real, that we're "opportunistic omnivores" built to thrive on many different dietary patterns, and that long-term adherence is the variable that matters most.
The bottom line
The math of weight loss is real—energy balance isn't controversial, and calories do matter. What's more complicated is the accounting. Your body is not a passive ledger that records every workout and calorie; it's a dynamic, adaptive system with its own priorities, shaped by hundreds of millions of years of evolution in conditions of scarcity.
Exercise is genuinely good for you, for reasons that go well beyond the calories it burns. But if your goal is weight management, diet is where the leverage is. Find an eating approach that keeps you full on fewer calories, that reduces ultraprocessed foods, and that you can realistically sustain—and let exercise do what it's actually best at.
FULL TRANSCRIPT:
Why You Can't Exercise Your Way to Weight Loss | Dr. Herman Pontzer & Mike Haney
In a recent episode of A Whole New Level, Levels editorial director Mike Haney sits down with Dr. Herman Pontzer, professor of evolutionary anthropology at Duke University and one of the world's leading researchers on human metabolism and energy expenditure. Pontzer is best known for his decade-long fieldwork with the Hadza — one of the last remaining hunter-gatherer populations in Tanzania — which upended long-held assumptions about how the body burns calories. He is the author of Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy.
The conversation covers why the intuitive math of exercise and weight loss doesn't hold up, how the body compensates for increased physical activity by dialing down spending elsewhere, what the Hadza can teach us about the limits of human energy expenditure, how weight set points and GLP-1 drugs fit into this picture, and what the research actually says about which dietary strategies lead to sustainable weight management.
"Exercise does everything — or at least helps everything — except it seems weight. Weight is much more the job of your diet."
Energy balance: the one thing the internet gets wrong
Mike Haney: Dr. Herman Pontzer, thanks so much for joining us today.
Herman Pontzer: Glad to be here.
Mike Haney: I thought we'd start today, before we get into the constrained energy model — which is where we're going to spend a lot of time, and its relationship to weight in particular — by establishing a concept that underlies everything, which is energy balance. I want to establish that because I think the idea of energy balance and how it affects our weight is intuitive to most people. But if you spend any time going down the YouTube influencer hole and start listening to other kinds of folks, you may have an attitude that energy balance is nonsense and calories don't matter and all of those kinds of things. But if we don't buy the premise of energy balance, then none of the rest of this works. Can you just explain what energy balance refers to?
Herman Pontzer: Sure. Energy balance is just the balance of how many calories come in and how many calories get burned off for an individual. Very simply, it's how many calories you eat and how many calories you burn, and the balance of those. If you're eating more than you burn, you're going to gain weight. If you're burning more than you eat, you're going to lose weight.
Mike Haney: And that — despite what the internet might tell you — is not really in question. There's some debate maybe about the kinds of calories that you eat, but at the end of the day, weight loss is a function of calories in, calories out.
Herman Pontzer: That's right. Nobody in the scientific world who's serious really questions that. It's really fundamental. It's physics essentially — fundamental physics — and it applies to our bodies the same as it applies to any other system.
The additive model vs. constrained energy: why exercise math doesn't add up
Mike Haney: As a way into constrained energy, I'll just describe what I think you call the armchair view of metabolism, and then you can tell me where it breaks down. If I'm somebody who wants to cut weight and I decide I need a 500-calorie-a-day deficit, I go: I'll stop eating the muffin in the morning and I'll cut my ice cream after dinner — there's a couple hundred calories — and then I'm going to go run three miles a day, and running is about 100 calories per mile roughly. So there's my 500 calories. And as long as I do that consistently, the pounds should just melt away until I am happy with my weight. But your work suggests that seemingly intuitive story is not necessarily the case. Where does it break down?
Herman Pontzer: Where it breaks down is in trying to track how many calories you're burning — that's actually quite challenging. And for that matter, tracking how many calories you eat is challenging as well. So it can really feel like the math isn't adding up. You read the back of the package, you try to be careful about how many calories you're eating, you go online and figure out how many calories it ought to take. Maybe your smartwatch tells you how many calories you're burning when you exercise, and you try to do the math, and it doesn't add up. Well, what you're missing is a few things. One is that your energy expenditure is hard to track and can change. Your body can adjust when you're losing weight — it will burn less as a way to try to not lose weight, because your body has actually evolved to not lose weight. We call that metabolic adaptation. Sometimes it has different names, but basically it's the idea that if you go on a crash diet or something like that, your body's basal metabolic rate, your resting metabolic rate will kind of reduce. And then there's this other idea we've been developing the last ten or fifteen years based on what we see in our research, which is that your body also adjusts to physical activity. If you become more and more physically active, eventually your body will adjust what it's doing in other parts of the day to reduce energy expenditure in other tasks. And instead of getting that 300-calorie bang for your buck from the exercise you're doing, you actually net less than that because your body has made adjustments elsewhere to keep total expenditure reduced.
Mike Haney: And so that ceiling is essentially the constrained energy model. Maybe it's worth just saying directly what the difference is between constrained energy — which is now how we understand it works — and the additive model that represents how we used to think it worked.
Herman Pontzer: The additive model is probably still the way most people think about it — it's certainly the way you'd have learned it in school if you learned about exercise and energy expenditure at all. The standard story — we'll call it the additive model — is that if I burn 2,500 calories a day today and I'm fairly sedentary, and I decide to change my lifestyle and add 300 calories a day of exercise, the additive model says I should now be burning 2,800 calories a day. It just adds up. That's why we call it additive.
What we've learned is that that's not really what happens. It'll work like that for a few weeks maybe, as your body is adjusting. But after your body adjusts to that new lifestyle, if we check in a few months down the road, you're not burning 2,800 calories a day as expected. You're burning substantially less than that. Maybe 2,600 calories a day. Maybe you're still at the same 2,500 calories a day you were before — that's possible, we do see that. It's because your body has adjusted to make room for that new exercise you're doing, and it doesn't show up anymore in the total calories a day that you're burning.
Mike Haney: I'm glad you mentioned the time component of that. I think this is the other place where this probably challenges some people's lived experience. I run marathons occasionally every couple of years, and I have consistently found that when I ramp up to train — it's a four-to-six-month training period — I weigh myself at the beginning and the end and I will always lose eight to ten pounds, depending on kind of where I start. And I don't consciously change my diet — other than I like to eat Ho Hos after a long run. So if you came to me and said, "No, exercise doesn't cause weight loss," I'd go, "But this happened. I see it on my scale." But what you're saying is this is a gradual process. It's not that exercise never burns off extra calories.
Herman Pontzer: No, that's right, and I think people do get it wrong that way. First of all, I'm not saying you can't burn more calories — I'm saying it'll be less than you expect, but it might be a bit more. The exercise itself does burn calories; you're making room for that by adjusting in other parts of your energy budget. And the third thing is that adjustment period. If you have your baseline lifestyle and you say you want to run a marathon in six months so you're going to ramp it up — yeah, for those first few weeks your body hasn't adjusted yet. You'll see it. And I would bet, Mike, that the weight change happens at a faster rate and you see it more in the first few weeks of that change than you do towards the end, even though your mileage actually goes up towards the end.
Mike Haney: Yeah, I suspect that's probably true. I don't weigh myself very often and I've started doing this the last handful of marathons to see what it is. So I'll do kind of a beginning and end, but it would be interesting next time I do it to kind of weigh along the way and see. And the other side of this that we will get into more is the intake side and how the body — like I said, I'm not consciously changing my diet, but I probably am changing my diet because the body will sort of change the signals and things that we're working with.
How the body really spends its energy budget
Mike Haney: What do we know about how much of our energy is going to various purposes? I think it's a little unintuitive. People might think exercise is half of their energy burn or seventy percent, but it's actually really little. Can you give us the basic accounting?
Herman Pontzer: The typical American adult woman burns 2,400 calories a day. The typical American adult man burns 3,000 calories a day — that difference is just due to average differences in body size. Obviously, not all men are bigger than all women or anything like that, but on average, that's what you see. Now, where do those calories go? In both cases, in both men and women, over half of your calories are burned just at rest. Just your body, your organs doing their jobs unseen and unnoticed throughout the day. Your brain burns 300 calories a day — even if you're not thinking hard, it doesn't matter. Three hundred calories, the equivalent of running a 5K, just to keep your brain running. Our organs are busy all the time in ways we don't really appreciate or aren't attuned to.
Then there's digestion, which costs you about 10% of your total calorie budget every day. So if you're burning 2,400 calories a day, 240 of those are going to just digestion and metabolizing your nutrients, breaking them down and making them usable for your cells. And then there's things like stress. Being awake and alert costs energy — you and I right now are burning more calories than we were when we were lying in bed waking up this morning. So all of those sort of unseen, unnoticed tasks account for well over half the calories you burn every day. Physical activity is a much smaller part. And that includes walking around your kitchen while you're cooking dinner, walking the dog, a lot of our daily movement. Structured exercise — unless you're an Olympic athlete — is a really tiny part of daily energy expenditure.
Mike Haney: You have a really good metaphor in the book about the body being not a machine but more like a business, in terms of how it deals with calories coming in and going out. Would you mind explaining that?
Herman Pontzer: Sure. Your body, like all organisms, has evolved with two tasks in mind: bringing energy in and using that energy to survive and reproduce. That's it. So to complete that task, you've got 37 trillion cells all doing their jobs, organized into different components — your immune system, your nervous system, your kidneys keeping your blood clean. It's like a big corporation: like General Motors, where each department is working together to produce something. In the case of your body, you're trying to produce humans — that's the idea.
The corporation has an income, which is the food you're eating every day, and that gets divided up to all those different departments to do their jobs. When resources are limited — when the income's low — your body has evolved to make really smart decisions: I'll spend less here, a little less there, I'm going to protect this piece. We don't spend less on our brains because that's really important, but maybe we spend a little bit less on reproduction or something we can put off for now, for the greater good of surviving and reproducing in the long game. Your body's making these decisions all the time about what departments to spend calories on. When we start to limit how many calories are available — either by reducing how much we eat, or effectively by spending a lot more on exercise — the other departments have to adjust to that new normal and reallocate how much they're getting. So yeah, your body's a business, and every department has to run in a smart way integrated with everything else.
Mike Haney: The way you describe this in the book — the typical view is that the body is a simple machine, and it's not, it's a dynamic machine. And that idea of the dynamism, that it is constantly making these adjustments — and again, those adjustments would likely vary depending on genetics, life circumstances, etc. You see this across species. You cited a study in mice where when you calorie restrict mice, they protect the reproductive system because they just don't live very long. So for them, they don't care about the immune system, they care about the reproductive system. Whereas for us it's different because we have these long lives.
Herman Pontzer: Yep, exactly. Evolution is always playing the long game. And so yeah, that's exactly right. Your body's trying to make these decisions in a smart way based on how many calories are available.
"Your body isn't just a dumb machine that's going to burn calories however it's set to. It's going to be responding all the time: how many calories are available? And it has ways of sensing that."
What the Hadza teach us about human energy expenditure
Mike Haney: I want to talk about individuality in all of this. How much person-to-person variance do we see in this effect — in how much constraint there is, in where the energy gets burned off — and did you see that variability in your work with the Hadza?
Herman Pontzer: There's a fair amount of variability, and I don't think we know a real answer to that question yet. If I just look at metabolism in general — how many calories you're burning — and I compare two people of the same age, same height, same sex, same lifestyle, I wouldn't be surprised to see three or four hundred calories a day difference between how many calories they're burning. That's just individual variation in metabolism that we don't entirely understand. Probably some of it's genetic, some of it might be how you grew up and how your body kind of learned to burn calories. There is that component to it of your metabolism, we think. And so your metabolism in general — there's variability there that we don't have a great handle on yet. We do know that your body size, your fat-free mass, those are the biggest predictors of how many calories you're burning. So it isn't that we don't understand the system, but there's still this variability that we don't quite have a handle on all of it yet.
Now, how do people respond when we try to push that system around? Well, now we've added another layer. We don't have a great handle there yet either on why some people seem to adjust more and faster than others. We've just wrapped up a big meta-analysis that pulled together all the data on intervention studies — exercise interventions where somebody's sedentary, they get enrolled in an exercise program, we see if they're constrained or not in their energy expenditure. There's no obvious signal that's glaringly obvious about why some groups adjust and why other groups don't adjust. So I think we're still in the dark a little bit about why that happens and why it happens more for some people than others.
Mike Haney: I'm curious — the work that you did with the Hadza, which is a hunter-gatherer tribe in Africa, where you went and measured their energy expenditure — one of the last hunter-gatherer populations with traditional ways of living — how much individual variability did you see in that data, given that that population is in some ways more controlled than maybe a western population where you might have more variance in daily activity and the kinds of diets you're eating?
Herman Pontzer: It was actually really similar. If you think about the ways that we plot the data to visualize what's going on — if you plot everybody that you collect data for, their body weight on the horizontal axis and how many calories they're burning a day on the vertical axis — there's kind of a cloud of data there. People who are heavier burn more calories, people who are lighter burn fewer, but it's a fuzzy relationship. The Hadza look just as fuzzy as everybody else. And so I don't think they're any more homogeneous or any less variable than if I had had a group of Americans, for example.
Mike Haney: What is the food availability landscape like for the Hadza? In the book it sounded like it wasn't conditions of near starvation — tubers grow year-round, there's honey, they go after game.
Herman Pontzer: The risk of starvation is quite low. I can't remember ever seeing that in the few years I've been working in that community. Now, there are periods when there's more food available — easier to get the tubers, the berries, the game is more plentiful — and then seasonally that changes. So it isn't constant, and you do have to work for your food. They don't have refrigerators, so they don't have easy access to stored calories they can get anytime they want. I think their body's perception of how many calories are available is probably a bit less than ours, even though they're never at zero.
The honey is a good example — it makes up maybe fifteen percent of their calories, which sounds like a lot. And it's definitely seasonal — it has more to do with how good the rains have been recently, that affects how much honey is available and how the bees are doing. And it takes work. You've got to climb up into a baobab tree, three stories up. You're risking your life. You've got to chop into a hollow limb of this big massive tree with a hatchet, and you try to smoke the bees out, but you're absolutely going to get stung — and then maybe it's a smaller hive than you thought and you did all that work and you don't get that much. Sometimes it's a real bonanza, but it's just so different than our life where I'm in my home right now, I can see my refrigerator, and inside that refrigerator thousands and thousands of calories. And down the street in the supermarket, millions. They just don't live in that world. It's just different.
Where the body compensates: immune function, hormones, and stress response
Mike Haney: Do we have a clearer picture now of precisely what the body is dialing down to account for that increased exercise load? Is it the immune system? The basal metabolic rate? Something else?
Herman Pontzer: Here's what we know so far. If you exercise more, we do have some evidence that your basal metabolic rate — and maybe even your metabolic rate while sleeping — tends to adjust downward to make room for that high level of activity. Now, what is the energy being taken away from to reduce your basal metabolic rate? For that we have to look at evidence of hormone profiles, for example, or other markers of different systems being turned up or turned down.
In the immune system, for example, we know that when people are exercising more they have less inflammation — that's a marker of immune system activity coming down. We know that people who do endurance training for many years tend to have reduced sex hormones — lower testosterone levels in men, lower estrogen and progesterone levels in women. We know that when people exercise regularly, the amount they respond to stress is reduced: lower cortisol levels, lower adrenaline levels, epinephrine levels. We don't yet know how to attach a calorie value to each of those changes — we don't know the conversion rate for, say, a thousand white blood cells. We're working on those kinds of studies. But we see this reduction across different systems, and we think that's where the body is saving calories.
Mike Haney: I'm curious if there's anything we can do to raise that ceiling — some supplement or food or approach that adjusts this compensation effect.
Herman Pontzer: In the big meta-analysis we're just finishing up — it's not published yet, but I can talk a little bit about what we found. One thing we notice is that when people add a diet component to their exercise regime, they tend to constrain more. If you don't diet with your exercise — if you eat as much as you want — you might have less compensation. But then what happens is you're also eating more, so the net result on body weight will still be near zero. You might be burning a bit more, but you're also eating a bit more, so it won't affect that balance.
Weightlifting might be a little less subject to this compensation than aerobic exercise is — there seems to be less compensation in studies with a weightlifting intervention rather than an aerobic one — but I think it's still early days to know if that's going to hold up. It's possible that one of the reasons that people cheat with things like steroids is that it provides a signal that the body says, "I don't have to compensate. Everything's great and I can continue to have a high level of output, build muscle at a high level." So it's possible that those kinds of changes might affect this system. But I wouldn't recommend that, obviously, for a lot of reasons. And no, in terms of superfoods or anything like that, probably not. There's no shortcut.
Mike Haney: I'm glad you mentioned the weightlifting there because that was the other thing I was curious about — we know that body composition affects energy expenditure. How does that impact this equation? In the case of weightlifting where I'm putting on more muscle mass, is that going to ultimately change what my body's ceiling is?
Herman Pontzer: It does, and so all of the analyses that we do account for body size and body composition because we have to — we don't want to just compare 200-pound bigger people to 100-pound smaller people and say, "Oh my gosh, there's a difference," of course there's a difference because there's a difference in body size. So whenever we do our analyses we're always accounting for individual differences in body size and composition. And when we talk about energy constraint or compensation, these are all adjusted for differences or changes in body composition.
Now, when you exercise and if you start an exercise program, your body composition will change a little bit, maybe. It's actually a really small effect — especially like an aerobic training, like a running or biking intervention — it's not going to have a huge effect on how much muscle you're carrying. So even if you add a kilogram of muscle, for example, well, that's about 40 kilocalories a day change in total energy expenditure. It's not much. You're not really going to notice that. So that effect is there, but it's really small.
Now, if you ask about weightlifting — it's possible that you would have such a change in body mass and such a change in fat-free mass, your lean muscle mass, with weightlifting that you would see a really noticeable increase in calories burned per day just because you're a lot bigger. But that would be a pretty successful and pretty intense weightlifting regime. Those people who enroll in an exercise study, we don't see those kind of results.
"It just happens to be true that exercise doesn't change body weight very much. And you should do it for all kinds of reasons — there are all sorts of great reasons — but it is true that the effect on body composition is really small."
Weight set points, GLP-1 drugs, and the Biggest Loser effect
Mike Haney: I want to talk about the intake side of this and its relationship to weight. You had a quote that stuck with me — that BMR and total daily energy expenditure don't dictate weight change, they respond to weight change. Can you unpack that?
Herman Pontzer: When we go on a crash diet, our body responds by saying: things are bad, there's no food available, I've got to reduce expenditures in as many places as I can. Your basal metabolic rate will come down, your total energy expenditure will come down based on not eating enough. Similarly, a similar kind of response can happen when you exercise a lot more. And that's because your body is not just a dumb machine that's going to burn calories however it's set to — it's going to be responding all the time to how many calories are available. It's a totally unique and probably unseen situation in evolutionary history that we live in — where I can go to the supermarket and have millions of calories at my disposal right now if I want to. For all of our evolution, organisms had to be really sensitive about how many calories were available and how they were spending them. And so your body isn't just this dumb machine that's going to burn calories however it's set to. It's going to be responding all the time. How many calories are available? And it has ways of sensing that — whether you're losing weight, gaining weight, that kind of thing. It's constantly assessing its environment and making a smart decision.
Mike Haney: I'm curious about the thing I thought about as I started thinking about this evolutionary point — that all organisms have evolved essentially in a landscape of scarcity, and in the last 150 years or whatever, we're now in this landscape of abundance. It made me think: why aren't we all a lot bigger than we are? Obviously we have an obesity challenge, but why don't I just eat full packs of Oreos a day? Because I can, and they're good.
Herman Pontzer: Well, that's a good question. First of all, we are all a lot bigger. We did a study that came out over the summer — this past summer, 2025 — and we looked at energy expenditure and obesity levels in populations around the globe. We had, I think, 4,000-some adults in this study from, I think, 34 populations. Some were hunter-gatherers, some were very traditional farming populations, folks who live with their herds in some cases — cattle and goats, they make a very traditional living with that. And then we had people from low-income countries all the way up through highly developed, rich countries like the US and Western Europe.
What you can see is — it won't surprise anybody — that as you go from a hunter-gatherer population all the way across the spectrum of development into people who are really rich like we are as a population here in the US, yes, there's more obesity in richer countries because we can eat the Oreos. But it's not just that. We also have more lean mass. We're taller. Our bodies are using those calories for everything. You are just a bigger organism — you and I both, having grown up here in the US — than we would be if we had grown up in a hunter-gatherer world. So the answer to your question is first that actually we do eat a lot more already, and that's what our bodies do — we just grow and we have a bigger system. We're a bigger company than we would be back in the hunter-gatherer setting.
And then, well, why don't we just keep on eating? Well, too many of us do and we get pushed to overeat and we have obesity issues. But not everybody. And the answer to that is your body does have this mechanism to sense when you're full and can attend to other tasks. That hunger-satiety signaling is at work, and it works for most of us pretty well. That's why we don't eat five bags of Oreos — because we feel full. But we don't eat hunter-gatherer diets in terms of calories per day. If we did, we'd actually be smaller than we are.
Mike Haney: What do you think about the idea of a weight set point? And how do GLP-1 drugs fit into that picture?
Herman Pontzer: As a heuristic — a way to think about how the world works and plan a diet and exercise program — I think it's a fine approach. Your body does try to sort of find and sit at a particular weight. Now if we want to go deeper and ask whether there's actually a cellular signaling mechanism by which your body knows exactly how much it weighs and is trying to get to that number — or whether your body is a set of systems that are finding their own balance, and if you perturb it one way the whole system gets perturbed and you end up at a different weight and then homeostasis pulls you back — that's a harder scientific debate to settle. But as a general rule of thumb, yeah, the set point is real.
Here's why it doesn't hold super well scientifically: we know there are ways you can change it. The GLP-1 drugs, for example — if you want to think about it that way — seem to change the set point that the body is happy to sit at in terms of body weight. But not by changing anything about fat content or weight signals itself. They seem to be affecting hunger and satiety cues in the brain — how we respond to food. So it might be that other systems are getting perturbed and they settle at a particular weight, and we think of that as a weight set point, but actually it isn't weight that's the cue — it's these other things that end us up at a certain weight.
Mike Haney: Yeah, the GLP-1s are interesting. It seems like what they're doing is hacking one of those tools that our body uses to try to control our weight — and the fact that when people go off GLP-1s they tend to regain the weight would suggest the body is trying to work back to that point. You can't permanently reset it by hacking that system.
Herman Pontzer: I guess the question is how you assess the mechanism. The mechanism is saying it's hijacking a hormonal signal the intestine would normally send after you eat. And so that would say there's a set point that my body is listening to about how many calories a day I eat. When I hijack the system a little bit and I perturb it so that it thinks I ate today and I didn't actually eat, then I'll end up losing weight. And the signal that the body was listening to the whole time was not my weight per se — it was how many calories are coming in. That's a different signal, and that's a different set point. And when I take that hijacking cue away, now my body doesn't have that to work with anymore — it goes back up to where it was before. The signal is still energy in, rather than pounds on the bathroom scale. And so in both cases, your body is going to respond and act like it has a weight set point. It's a more difficult scientific question — and probably not necessarily important for day-to-day life — to wonder if the mechanism is really weight or is it something else.
Mike Haney: You mentioned the Biggest Loser study. The way I understand it: BMR went down as they lost all that weight, but when many of them regained the weight, BMR didn't come back up — which is a bit terrifying. And then in the Minnesota Starvation Study, those men did seem to recover their BMR. Am I interpreting those correctly?
Herman Pontzer: You got both of those studies pretty much right. People who lost weight had their basal metabolic rates go down in both cases, and both were cases of pretty extreme weight loss — which might have exacerbated the body's response. An open question is whether if you lose weight in a slower way, without alarming your body by losing it as rapidly, you'd have the same big effect. I don't know that you would.
One thing I would say about the Biggest Loser group is that those who regained the most weight had their BMRs come back closest to normal. So as a group, the average BMR still remained a little bit low at six years post-show, but so did their body weight on average. If you plot how much weight they regained versus how much their basal metabolic rates recovered, those seem to be related. In the Minnesota study, they intentionally let participants recover all the way back to their pre-starvation weight — and that's why I think you see the difference in effect. If you had let the Biggest Loser contestants come all the way back to their previous weight, their basal metabolic rates probably would have looked really similar too.
Mike Haney: And there was an interesting effect you mentioned in your book about the Minnesota Starvation Study — that those guys seemed to gain a little bit of extra weight, and there was an idea that maybe their bodies went, "All right, well, if this is a world we live in that's a little bit uncertain and we might face starvation again, let's pack on a couple extra." I think people see this rebound effect when they try to lose weight and they gain it back, and that might explain why you see that.
Herman Pontzer: Yeah, the overshoot that we see — especially in fat mass, you kind of don't overshoot your lean mass as much — but you certainly overshoot fat mass a bit. And I put on my evolutionary biologist perspective: whether that overshoot is an evolved adaptation, or there's just a little bit of slop in the system and people tend to overshoot — I think that's not entirely sorted out. But it certainly makes good sense evolutionarily that you'd overshoot a bit if you find yourself in a world that now you can't trust. Maybe you're going to starve again next week. So put on a couple more pounds when you can.
Diet, macronutrients, and what actually works for weight management
Mike Haney: The last thing I want to talk about on the intake side is macronutrients and how much — we've been talking about calories as calories, but calories depending on the source they come from do affect us differently. So how does this picture adjust when we think about taking in a protein-heavy diet versus a low-carb diet versus a high-fat diet?
Herman Pontzer: Those nutrients have different jobs in the body. Obviously, if we don't eat enough protein, you're going to have a hard time building and maintaining muscle — you can start right there. The other piece of the puzzle is that different nutrients seem to have different effects on how full we feel. We know that a higher-protein diet, a higher-fiber diet — and in some studies a higher-fat diet, although it's not always seen — tend to make us feel fuller on fewer calories. It's possible that changing your macronutrient profile a bit in that direction, especially towards higher protein — there's probably no real danger in going towards a higher protein diet, within reason — that seems to be a good way to get full on fewer calories.
Mike Haney: And I think that comes back to where we'll leave this, which is: okay, what do you do with this practically? You mentioned earlier all the reasons this is not saying don't exercise. Exercise is really good for you, and some of those mechanisms are because the energy compensation means it dials down your immune system so you have less inflammation — which is good for you ultimately. But on the intake side, what does this point to in terms of what a useful diet looks like, particularly for somebody trying to cut weight?
Herman Pontzer: Diet and exercise are two different tools for two different jobs. Exercise does everything — or at least helps everything — except it seems weight. Weight is much more the job of your diet. The general goal for diet, if you're trying to manage weight, comes down to one simple question: how do I feel full on fewer calories, or on a healthy number of calories? And the answer is going to be really individualistic — some people are going to respond differently to how different diets taste or how they work into their lifestyle — but that's the principle you want to get to.
There are some guidelines we know work. If you eat a higher-protein diet or a higher-fiber diet, those foods tend to make you feel full on fewer calories, and there's good evidence for that. We also know that if you cut half the menu — you say I'm not going to eat that, you really limit the foods you eat — that can have the same effect. Your sense of how hungry you are and how full you feel is affected by flavors and tastes. If you can only eat the same kinds of foods, you're going to hit that point of feeling full faster. That's why low-carb diets work: there's no magic to it, nothing evil about carbohydrate per se, but when I take all the high-carb foods off my list, all I can eat are the really high-fat and high-protein foods, and I'll feel full even though I feel like I ate as much steak as I could possibly eat. You're feeling full on fewer calories, and over the long run that's why those can be really effective. Similar thing if you eat a vegan diet — if you really rule some things out of your life and you stick to it, that can be a good way to do it. And Kevin Hall's work really points decisively to ultra-processed foods — foods that are engineered to be too delicious to put down — as pushing our brains to overeat. Getting those out of your diet is another good way to start.
So there are a lot of different ways people can do it. Some people love the low-carb approach, some people love different approaches, but the goal is always the same: how do I eat fewer calories and still feel full? People should feel free to experiment on a healthy diet that gets them to that goal.
"The best diet is the one you can stick to. If you don't like it, you're not going to do it. The percentage of people in this world who will stick with something they find miserable is vanishingly small."
Mike Haney: Well, I think that's where understanding this higher-level mechanism really helps. It's some underpinning to that old adage — the best diet is the one you can stick to. Because if your goal is to lose weight, it does come back to where we started: energy balance. You just need to take in fewer calories, and exercise is not going to get you out of that. You can't burn off all the Ho Hos in the world.
Herman Pontzer: That's right. I like to tell people: I'm not a dietician and I'm certainly not a medical doctor, but I do study people for a living. And what I know is, if you don't like it, you're not going to do it. The percentage of people in this world who will stick with something that they find miserable is vanishingly small. I know I'm not in that boat — if I hate something, the chances I'm going to stick with it long-term are pretty low. So you've got to find a way to get to the diet and exercise balance that you actually enjoy. And that's where the tribalism is so unhelpful — if the answer that you hear on social media is, "If you don't do it this way, you're doing it wrong," that's so unhelpful, because there are a million ways that you might work a healthy diet and exercise into your life that feel good and get you to the right places. People should feel free to experiment.
Mike Haney: And the last thing I'll throw out there: you use a phrase I really like — opportunistic omnivores. That's what we are as a species, which points back to that idea that everybody's going to be a little bit different. We're designed to eat all kinds of things. And so you just have to find what works for you. There's no particular macronutrient that's going to hack the system.
Herman Pontzer: We're designed to eat all kinds of things. That's right.
Mike Haney: All right. Well, I think that's a great place to leave off. Thanks so much for joining us today.
Herman Pontzer: It was fun. Thanks for having me.
This article is based on insights from Dr. Herman Pontzer, an evolutionary anthropologist and professor at Duke University. He is the author of Burn and Adaptable, and a leading researcher on human energy expenditure and metabolic health. His foundational Hadza hunter-gatherer energetics study was published in PLoS ONE in 2012.
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