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Chasing Life

Many of us are setting new personal goals in the new year – like exercising, eating healthier or even trying to lose weight. What does our weight really tell us about our health? Is it possible to feel healthy without obsessing over the numbers on the scale? Are our ideas about weight and health based on outdated beliefs? On this season of Chasing Life, CNN’s Chief Medical Correspondent, Dr. Sanjay Gupta is talking to doctors, researchers, and listeners to take a closer look at what our weight means for our health. Plus, what you need to know about the latest weight loss drugs and how to talk about weight and better health with others, especially kids.

Dr. Sanjay Gupta

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Why Our Bodies Fight Us on Losing Weight
Chasing Life
Jan 23, 2024

Everybody knows losing weight is tough. But why? While diet, exercise, and willpower might have something to do with it. The root may lie in how we humans have evolved as a species. Could our bodies be hardwired to resist shedding pounds? In this episode, Sanjay speaks to Daniel Lieberman, a paleoanthropologist and professor of human evolutionary biology at Harvard University. He’ll explain how our bodies evolved to hold onto fat as a strategy for survival. Plus, we'll get tips for exercising and eating right, with our evolutionary needs in mind.

Episode Transcript
Alicia
00:00:01
I have never been able to maintain my weight and my body composition in a way that I have been satisfied with.
Sharma
00:00:10
'Around the ages of 15-16, my metabolism changed and I had a hard time keeping the weight off.
Beverly
00:00:16
I've been on a diet all my life.
Karen
00:00:17
I've had some successes, but nothing permanent.
Alicia
00:00:20
I have tried calorie restricting diets. I have tried keto.
Karen
00:00:24
'I was eight-years-old when I was put on my first diet.
Beverly
00:00:27
I've tried it all. I've done every diet out there known to man.
Dr. Sanjay Gupta
00:00:34
When it comes to losing weight, almost everyone seems to agree on one thing. It's hard. And if you've ever tried to do it, no matter how many pounds you are aiming to shed, maybe it felt unnatural, impossible, even, like you were just bound to fail. Almost like your body and your brain were actively working against your goals like they were fighting to keep on the weight. Now, if that sounds familiar, I'm here to tell you that you're probably not imagining it. In fact, much of what I just described happening inside your body and your brain is actually outside your control. In fact, according to one 2021 study, it is common for people who lose 10% of their body weight to regain most of it within a year. And that same study show that they're likely to regain all of it within five years. And after that kind of loss and gain, it's often harder to ever lose it again. I know that's not what you want to hear, but the fact is that the weight loss struggle is real. At first, you'll start asking questions am I just not eating the right things? Am I just not putting enough hours at the gym? Am I just not trying hard enough? Then you're going to ask, is there something that's wrong with me? But what if it's not? What if hundreds of thousands of years of evolution are actually conspiring against you?
Prof. Daniel Lieberman
00:01:59
We evolved not to lose weight intentionally.
Dr. Sanjay Gupta
00:02:02
That's professor Daniel Lieberman. He's a paleoanthropologist who teaches human evolutionary biology at Harvard. What that means is that he's really interested in why the body looks and functions the way it does.
Prof. Daniel Lieberman
00:02:15
All animals need some fat. But humans have evolved to have exceptionally high levels of fat, even thin humans. And so we are under exceptional sort of biological pressure always to to put it on and keep it. As long as we have it for when we need it.
Dr. Sanjay Gupta
00:02:33
Now, of course, our individual metabolism, our genetics, our habits do play a role in our weight and how we manage it. Even Professor Lieberman, he's a marathon runner who has run the Boston Marathon not once, not twice, but 13 times.
Prof. Daniel Lieberman
00:02:49
It'll be my 14th year this year. Yeah.
Dr. Sanjay Gupta
00:02:51
Wow. That's incredible.
Prof. Daniel Lieberman
00:02:52
Yeah, it's kind of stupid, actually.
Dr. Sanjay Gupta
00:02:54
Okay. Is it stupid?
Prof. Daniel Lieberman
00:02:56
Well, it's not stupid, but, I mean, you know, we never evolved to stand on one line and run 26.2 miles to another one as fast as possible.
Dr. Sanjay Gupta
00:03:03
Even he would concede, though, that all that running may not really change what we humans evolved to do and what we didn't evolve to do. We are, he says, hard wired to maintain a certain weight. And that's in part why the struggle is so real.
Prof. Daniel Lieberman
00:03:22
What we're adapted for, fundamentally, is not to be healthy, not to be happy, not to be nice, not to be, you know, famous, not to be anything other than reproductively successful.
Dr. Sanjay Gupta
00:03:33
Bet you weren't expecting that. On today's episode, I'm going to explore why it's so hard for us as humans to lose weight and most importantly, what you can do about it. I'm Dr. Sanjay Gupta, CNN's Chief Medical Correspondent and this is Chasing Life.
Dr. Sanjay Gupta
00:03:55
You know, the basic question that Professor Daniel Lieberman asks is why the human body looks and functions the way it does. How and why did we evolve this way? And that's really important to understand, because by understanding our evolutionary past, we may better understand our future. And maybe, just maybe, we can figure out how we can work with our bodies instead of against them. So first I wanted to start with a little paleolithic perspective. What was life really like when we were all hunters and gatherers?
Prof. Daniel Lieberman
00:04:29
All the food they got, they had to go out and either hunt and gather, and that meant every day walking around somewhere between 5 to 10 miles a day on average. They sometimes had to run. They had to dig a lot. They had to occasionally climb trees. They had to do, you know, everything was done by hand. They had to carry their food. They had to carry their babies. There was no shopping carts. There were no, you know, no machines of any sort. But in general, hunter gatherers tend to be reasonably fit, but not super fit. They're not like, you know, Tour de France athletes. They're reasonably strong, but they're not super strong because muscle is expensive. You know, you don't want to have any more muscle than you need because it costs a lot of energy.
Dr. Sanjay Gupta
00:05:08
They ate what they killed or what they grew. But the point I think he's making is that nothing came easy. And as a result, no surprise our early ancestors were pretty fit. I should mention that even though our ancestors started hunting and gathering at least 2 million years ago, there are still a small number of tribes in our modern world who live like this.
Prof. Daniel Lieberman
00:05:32
And it was actually a pretty great way to live if a hunter gatherer survived childhood. They tend to live about 68 to 78 years of age. So they're they do pretty well, and they tend not to have the kinds of chronic diseases that are common in places like America. Heart diseases is very rare to almost nonexistent.
Dr. Sanjay Gupta
00:05:49
Should we aspire to be the way that we once were? I mean, is that a good goal?
Prof. Daniel Lieberman
00:05:55
No, I don't think so. Because first of all, farming is here to stay. Farmed foods are here to stay. We can learn something from hunter gatherers. And I think one of the most important things we can learn about them is this concept of mismatch. So imagine you're a zebra living out in the savannah, right, eating grass. And all of a sudden somebody swoops in, puts you in a plane and drops you in, like, northern Canada in a tundra, like, what are you going to eat, right? You're totally mismatched to that environment. Well, we've kind of done that to ourselves.
Dr. Sanjay Gupta
00:06:23
Try and remember that. This idea of the mismatch. We're not running from wild animals anymore. We are spending our days sitting and scrolling through our smartphones. We're not walking miles and miles just to find water like we used to. Instead, we drive sometimes for even short distances. Sugary food and fatty foods, which used to be scarce sources of valuable energy, are now not only plentiful, but within easy reach almost all the time. The world has changed and our environment has changed. But here's the point. Our bodies are still stuck in the past, biologically. It's a mismatch.
Prof. Daniel Lieberman
00:07:04
We've changed our world through agriculture to some extent, but really through industrialization. So we no longer eat the same kinds of foods. We no longer have the same kinds of physical activities. We have all kinds of stress from, you know, all the things that can add up to stress. And the result is we get certain kinds of diseases. And looking at hunter gatherers and and also subsistence farmers can help us figure out what those adaptations are that we are, you know, are adapted for what we're not adapted for, and to figure out how to meld those two worlds. And there's an important additional point, which is that just because hunter gatherers do it doesn't mean it's necessarily best for us.
Dr. Sanjay Gupta
00:07:44
Professor Lieberman says there are lots of mismatches. There's almost too many to count. There are small mismatches, like having flat feet, which can occur simply from less use, or nearsightedness. That can sometimes happen from spending too much time inside when you're very young and your eyes don't develop properly as a result. And there are big mismatches as well, which Professor Lieberman and other evolutionary biologists call mismatch diseases.
Prof. Daniel Lieberman
00:08:12
So mismatch diseases are defined as conditions or diseases that are more common or more severe when we live in environments for which we're poorly or inadequately adapted.
Dr. Sanjay Gupta
00:08:22
Now, these happen because our body's still stuck in the past, are poorly adapted for the current environment. Our ancestors didn't have large amounts of sugar available to them at any time, but we do now. And as a result, we're much more prone to diabetes. Same goes for heart disease. Early humans had to be physically active to find food, which protected us from many kinds of heart disease. But that's definitely not the case now. So you understand the picture that he's painting, and some of it's going to sound pretty discouraging. But he also reminds us there is some good news about mismatches as well.
Prof. Daniel Lieberman
00:08:58
When you can identify a mismatch, that means you're identifying a way to prevent the disease. And the best way to deal with the disease is to prevent it from happening in the first place. And so we can modify our diets, right? We can modify our physical activity levels. We don't have to go back to the Stone Age, but we can adapt some lessons from the Stone Age to the modern world we live in. You don't need to swim the English Channel or run a marathon to be healthy. It turns out just moderate levels of physical activity have enormous effects. You don't have to be a hunter gatherer to get the benefits of being physically active.
Dr. Sanjay Gupta
00:09:32
People who have tried to lose weight will almost universally tell you it is hard to do. It's hard to lose weight. It's easy to put it on. From an evolutionary science standpoint, why is that?
Prof. Daniel Lieberman
00:09:47
'Well, let me back up by giving it some important facts. So humans are an unusually fat species. Even thin human beings, like thin hunter gatherers, like then hunter gatherer males would be about 10 to 15% body fat. Then hunter gatherer females would be like, you know, 15 to 25% body fat, right? That's a very healthy, thin human body that is way fatter than most mammals. Typical mammals have about 4% or 5% body fat. Other primates don't have much fat. We pack it on right compared to most species. And the reason for that is that fat plays a key role in our reproduction. And we have a very unusual reproductive system whereby we compared to, say, chimpanzees, our closest relatives, we have babies about twice the rate. We have multiple babies at the time. We have these big brains which cast a huge amount of energy. Right now, you and I, just sitting here, one of every five of our breaths, is paying for our brain, right. It's 20% of our metabolism. And a baby when it's born, half of its energy is paying for its brain. It needs a lot of fat. So babies, human babies are born very fat because they have to have that energy to make sure that they can keep their brain going. Because the brain doesn't store energy. You always have to supply the brain with fat. Furthermore, if you're a hunter gatherer mother and you every day, you need to go out and get food for your children, or if your infant and maybe your five-year-old and maybe your eight-year-old, none of them can really feed themselves, right? You need a lot of energy. You can't just wait for Uber Eats to deliver your food to you. You have to go out and exercise. Yeah, you have to be physically active to get the food necessary to overcome that. And so we draw down on our fat reserves when we're physically active to produce milk, to feed our brains, to do physical activity.
Dr. Sanjay Gupta
00:11:31
Fat has always been important to humans, and an almost basic level. After all, it's a storable energy. It helps keep our brains working. It powers our bodies. It's a key to reproduction, to being healthy enough to have children and to keep those children alive. So it's not surprising, then, that fat is valuable and that our bodies want to hold on to it whenever possible, for as long as possible for future use.
Prof. Daniel Lieberman
00:11:56
It's like money in the bank account, and so individuals who have appropriate levels of fat did better in our evolutionary history than those who didn't. And we played a really important role in human evolution. And so we were selected to make sure that we always could put it on, because there were always times when we had to lose it. And at the same time, we never evolved to lose it willfully. To go into negative energy balance is a crisis mode, right?
Dr. Sanjay Gupta
00:12:23
'Professor Lieberman gave me this analogy that I really liked when it comes to understanding negative energy balance. Start off this way - think of energy in the form of fat. Like he said, money in the bank. So when you spend more energy than you're taking in, let's say you've just spent all day hunting without any luck. You're in negative energy balance. That's when you lose weight. And when you're spending less energy than you have coming in, maybe you've been feasting and resting without having to hunt. You're in positive energy balance. You gain weight. And just like your bank account, you certainly don't want to spend more than you have, and you want to save any extra you do have for a rainy day. Early humans did not want to lose weight. And despite our best intentions, neither do our bodies now. It's just another example of how our bodies aren't built for the way we live now. In other words, it's a big mismatch. There's even mechanisms that we've developed to resist it.
Prof. Daniel Lieberman
00:13:26
So what happens when you diet? Your cortisol levels go up. Cortisol is a stress hormone doesn't cause you to be stressed. It goes up when you are stressed. And one of the effects of cortisol is it makes you hungry. So when you diet you are battling. At least a dozen, if not more, adaptations that evolved over millions and millions of generations to prevent you from losing weight.
Dr. Sanjay Gupta
00:13:49
That's so interesting.
Prof. Daniel Lieberman
00:13:50
And so, of course, it's hard. It's because we evolved not to lose weight intentionally. And losing weight requires, dieting requires tricking your body and overcoming those adaptations which your body's going to fight you in every, every inch of the way. And of course, it's hard. It's really, really, really hard. And we need to be extremely compassionate towards people. It's not about willpower. That's an unfair characterization, I think.
Dr. Sanjay Gupta
00:14:18
Not sure about you, but I do find it reassuring to think that this is not just a purely personal struggle, a lack of willpower, or an individual failure. Our bodies evolved not to lose weight. Remember that. And we aren't just imagining that our bodies are fighting us. They're actually programed by evolution to do just that. When we come back, Professor Lieberman will answer if we should eat like hunter gatherers and how to reframe weight loss with evolutionary biology in mind.
Dr. Sanjay Gupta
00:14:59
'Welcome back to Chasing Life. We're speaking with Professor Daniel Lieberman, a paleo anthropologist, about why evolution has the deck stacked against us when it comes to weight loss. One popular diet you might have heard of is the so-called paleo diet, where we try to eat like our ancestors did. But how helpful is that really for weight loss? And is it even good for us? Do you think that the way that we used to eat as hunter gatherers and people refer to this as caveman or paleo sort of diet? I think I know the answer. I am almost certainly know what you're going to say. But is there a practicality at all to trying to recreate some of the way we used to live in our modern day?
Prof. Daniel Lieberman
00:15:43
Well, yes and no, in the sense that there are ways in which our modern diet has gone really seriously awry. But, you know, a lot of the problems that we have with obesity and heart disease and whatever, you don't have to go back to the Stone Age to see them not occurring. You can just go back a few hundred years to to farmers. I mean, if you look at a like a Mediterranean, a traditional Mediterranean diet, right, which is high in fiber, doesn't have a lot of added sugar. It has lots of fruits and vegetables that the same would be true of a traditional Mexican diet or a traditional Asian diet or traditional African diet. These are super healthy diets. You don't need to eat a paleo diet. And furthermore, there is no one paleo diet. We just published an analysis of the paleo diet. We found there are 12 different tribes, hunter gatherer tribes from different parts of the world where we have really good dietary data and none of them match the paleo diet. Not a single one. And, you know, there's incredible variation.
Dr. Sanjay Gupta
00:16:46
Pretty good marketing around the paleo diet.
Prof. Daniel Lieberman
00:16:48
Oh, it's serious marketing. But the thing is, you know, we evolved to eat anything. I mean, your liver, right, if you eat, if you eat carbohydrate, your liver can turn into fat. If you eat fat, your liver can turn into carbohydrate and protein. We you know, we evolved to eat anything. People lived in the Arctic eating all meat. And there are vegans and there are vegetarians and there are, you know, it's amazing the variation in human diet and how people can kind of do okay. And a wide variety of diets. But, you know, look, if you want to look at healthy diets and every culture in the world figured out how to eat reasonably healthy diets, all of them involve a lot of plant food, not much added sugar, none of this process stuff that we eat today. Diversity of foods, combinations of foods. You don't need to go back to the Paleolithic, again that's the short answer.
Dr. Sanjay Gupta
00:17:38
From an evolutionary perspective, why do diet and exercise matter so much? Given the fact that we didn't really diet to lose weight. We didn't really exercise for exercise sake in our evolutionary past. Why is it so important now?
Prof. Daniel Lieberman
00:17:54
Because both inactivity, habitual long term inactivity and obesity. However you want to define it. Having too much fat. Both of them are mismatches and for different reasons. So obesity is a mismatch because it first and foremost causes inflammation. Your fat cells which technical term is adipocytes are like little bags. And you have billions of these little bags all over your body. And as you store fat, those that cells swell like a balloon. And when those balloons get too big, if I overfill a balloon, it's going to rupture, right. And the fat cells are no different. The fat cells can only hold so much fat, and you only have so many. And you're getting you can't develop more of them after you're born. As those fat cells swell, if they start to burst. It's like cutting your skin as they causes an inflammatory reaction. And this low level of chronic inflammation is pernicious. It causes damage throughout the body. And it's strongly associated with heart disease with, you know, hypertension, with Alzheimer's, with diabetes, with cancer. So the inflammation from obesity is probably the number one reason to be concerned. And belly fat is especially concerning. So that's one of the mismatches right. That's the obesity mismatch. Right. And so we never evolved to have that much fat. And so we never you know evolved to deal with it. Right. Because our ancestors maybe they would have loved to be that fat. But they never had the chance to be that fat.
Dr. Sanjay Gupta
00:19:23
Now, Professor Lieberman reminded us of something that you've probably heard before. Not all fat is the same. That fat that's under your arms, for example, or on your thighs. That's subcutaneous fat. And ironically, even though it's visible and causes some of us mental anguish, it's pretty harmless. But it's the fat you can't see, the fat around your organs called visceral fat, and the fat in your organs or your muscles called ectopic fat. That's the dangerous kind. When those cells become overfilled, they become inflamed. And we know that chronic inflammation is strongly linked to conditions like heart disease, hypertension, even cancer and Alzheimer's. So that's why diet matters. But then what about exercise?
Prof. Daniel Lieberman
00:20:08
Flip to the other side. Physical inactivity is a mismatch. Habitual physical inactivity as much because remember, you know, your body can take a calorie and they can use it for just certain things. And if you're not using the calorie at that moment, what's it going to do? It's going to stored as fat. And if you end up, physical inactivity can predispose you towards obesity. One of the ways to prevent being fat is to exercise. Exercise is not great for losing weight. But it sure is good for helping you prevent any weight gain. That's very clear from the science.
Dr. Sanjay Gupta
00:20:38
But exercise can also be good for another reason, not just preventing weight gain. Professor Lieberman says exercising can actually create stress in your body. The good kind. Yes, there is a good kind of stress. Stick with me here for a second.
Prof. Daniel Lieberman
00:20:53
'Think about it. When you exercise, go for a run or swim or workout on an elliptical or whatever it is you like to do, right. You're stressing your body. You're stressing almost every system of your body. You cause damage to proteins. You cause damage to your DNA. You cause damage to your muscles. You tear them apart. You cause cracks in your bone. I mean, I could go on. There's like a you heat up everything you can think of that is about exercise is stressful. But since we evolved to be physically active, our bodies evolved mechanisms to respond to every single one of those stresses. And in fact, they evolved to kind of compensate, like to overshoot. So what do you what does your body do when you exercise? Your body produces antioxidants. I think by the gazillion, right. So you you exercise turns on your body's production of powerful antioxidants. When we produce antioxidants, we produce more than enough. When we produce enzymes to repair our DNA, we produce more than enough. So we end up being better off after the exercise than before. But here's the rub. We never evolved not to be physically active. It wasn't possible in the past, so we never evolved to turn these anti-aging mechanisms on in the absence of physical activity. So if you want to slow aging, exercise is key. Exercise just turns on those mechanisms. And in the absence, we age faster.
Dr. Sanjay Gupta
00:22:16
Our bodies want us to do things that maybe aren't conducive to being healthy in the modern age. We take the elevator instead of the stairs. We crave sugar and fat. How do you square that? What are the takeaways? And are there things that we can learn from our ancestors?
Prof. Daniel Lieberman
00:22:34
'I think the first thing is that we have to learn to be compassionate and stop blaming people for doing what's normal and natural. If you stand next to the escalator in a stairway next to each other, most people will take the escalator, right? It's an instinct. You know, if you put them in the Kalahari Desert, people would take them there too. So instead of blaming people and making them feel bad, we have to help people feel good about taking the stairs and making it natural. And then the same is true of food, right? If you put a piece of chocolate and cake in front of me and a carrot, of course I want to go for the chocolate cake. I mean, I'm not crazy, and it's an instinct, right? It tastes better and has more energy. And it's, you know, like its chocolate cake. And so I think that we have to figure out how to engineer our worlds, to help us make the choices that we would like to make. We evolved to be physically active for two reasons and two reasons only - when it's necessary or when it's rewarding. So we have to figure out ways to help us and help each other make physical activity necessary and rewarding. And the same is true of food. We evolved to eat foods in order to have as many offspring as possible, and so we go for energy rich foods that are high in calories and high in fat. But we didn't have access to that stuff very often. And so we have to find ways to help each other, make those foods delicious, and make the foods that should be special treats. Make them just special treats. We need to act collectively. It's a political problem, partly, but also it's a social problem. We need to figure out ways to help each other, and it's going to require looking in the mirror and being compassionate and clear minded. And also, I think, you know, an evolutionary perspective can help us.
Dr. Sanjay Gupta
00:24:14
And I think this may be the most important point. Having some grace for ourselves, for others, when we think and talk about weight, and not just because you're being kind, it's because there are actually a lot of factors that influence someone's weight. When Professor Lieberman explained why humans evolved to conserve fat, that got me thinking. That's when our bodies are holding on to weight. They're doing what they're supposed to do. They're functioning to keep us alive, to store up energy, to help us reproduce, but not necessarily to help us look good. However, you might define that. I understand this can be frustrating, even annoying for some people who are trying to shed pounds or keep them off. But I hope it also offers some measure of comfort, or at least some insight as to why losing weight often isn't easy. I hope it also demonstrates how carefully calibrated our bodies are, how important weight and fat actually were to us as humans. Without those things, the generations that came before us might not have survived. So yes, we might not be able to escape the pull of evolution. But if you think about it, we can use it to our advantage and even build it into our modern day environment. Next week on Chasing Life, we're going to talk to an obesity expert about what everyone seems to be buzzing about, the new medications that help us lose weight.
Dr. Jorge Moreno
00:25:42
I remember, I remember exactly, I was in my office reading the article about semaglutide, Ozempic and you know, my first response was, it works. It really works.
Dr. Sanjay Gupta
00:25:53
We're going to have an honest conversation about the benefits, the risks, the rewards, and what we still need to learn.
Dr. Sanjay Gupta
00:26:01
Chasing life is a production of CNN audio. Our podcast is produced by Eryn Mathewson, Jennifer Lai, and Grace Walker. Our senior producer and showrunner is Felicia Patinkin. Andrea Kane is our medical writer and Tommy Bazarian is our engineer. Dan Dzula is our technical director. And the executive producer of CNN Audio is Steve Lickteig, with support from Jamus Andrest, Jon Dianora, Haley Thomas, Alex Manasseri, Robert Mathers, Leni Steinhardt, Nichole Pesaru, and Lisa Namerow. Special thanks to Ben Tinker, Amanda Sealy, and Nadia Kounang of CNN Health and Katie Hinman.