On Humans - Beyond Paleo: A Culinary History of Humanity ~ Daniel Lieberman

This is the On Human's podcast, a show which makes new research about humanity more accessible to everyone and more meaningful to the big questions about who we are. I'm your host, Ilari Makgele, and today's episode is about a topic at the center of our lives, food. Now all animals need food, but we humans are the chefs of the animal kingdom. We cook our food. We chop it.

We grind it. We ferment it. We roast it. Why? Now this is 1 of the many questions we explore in the sweeping episode, which tells the story of humanity through what was on the dinner plate.

Our guide on this journey is Daniel Lieberman, professor at Harvard University and the founding chair of Harvard's department of human evolutionary biology. We start the conversation with a topic that feels unavoidable when talking about food with an expert in human evolution, is the paleo diet. Daniel Leverone is someone who has actually studied the diets of hunter gatherers, and the answer that he found was surprisingly different from what the paleo cookbooks would tell you. There is no 1 paleo diet, he says, and not everything that people of the paleolithic ate was necessarily healthy. But this is not just an episode debunking a particular diet.

We cover something like 2000000 years of human culinary history in this episode. We begin with the contested role that meat played in human evolution, and then we explore how processing and preparing food helped shape our bodies in all sorts of unexpected ways. We learned about the origins of our enormous brains and our muscular butts. We also hear why Lieberman thinks that humans have always been a very fat ape. We then turn to agriculture and how relying on farmed foods transform the human condition in so many ways, and finally, we arrive at the extraordinary modern food system, a system that has given so many of us an abundance of choice and an abundance of food security, but also has created an environment in which calories are cheap.

Ultra processed foods are everywhere, and staying healthy can feel like a constant battle of willpower. And we do finish with some practical advice on how to stay healthy, advice that I think is refreshing and compassionate, especially for anyone who struggles with their weight, something that Lieberman stresses. It's not a moral failing or a sign of laziness, but is in many ways a very natural response to the environment most of us now live in. But there are also good news there. So stay tuned until the very end.

Now this is really 1 of my favorite conversations I've recorded this year because it brings together so many other things this show is about, about deep human history, serious science, and something completely ordinary that all of us do every single day. And I hope that maybe after this, you don't only know something more about human history and human biology, but also can look at your own dinner plate in a refreshingly new light. So I really hope that you enjoy this. If you do and want to dig deeper into the sources, can check. The show notes has a lot of useful things.

And if you're new to the show and want more of this kind of deep diving conversations about the human story, then do subscribe to OnHumans for more. And if you're a returning listener and want to show a little bit of support, the easiest thing you can do is to give the show a good review on whatever app you are using and, of course, sharing it on social media or sharing it to a friend who you think might enjoy it. But anyway, now let's begin this episode. As always, I wanna thank all the wonderful people who support this work at patreon.com/onhumans. Thank you so much for all of your support.

It really means a lot, and this episode, as always, is dedicated to you. Now, let's go. Professor Daniel Lieberman, welcome to On Humans.

Thank you.

So as someone who is interested in human evolution myself, 1 of the things that people often ask me is, oh, so are you really into like paleo diet? And I've never really know what to say. I'd be like, not really, but I don't really know why I'm not. You on the other hand are actually a scientist and you've actually studied this issue. What happened when you studied what exactly would the real paleo diet look like if there ever was 1?

Well, I've always been interested but skeptical about the paleo diet. A few years ago, actually, it was during the pandemic, actually, because the lab was closed. I had a student who was gonna do an experimental project. And so I thought it'd be fun to have her, as a as a project she could do for her her senior thesis, collect all the really high quality data on hunter gatherer diets from the tropics.

And tropical hunter gatherer, so we're not thinking about the Inuit, for example, which have a very unique diet but wouldn't be so representative of the big picture of human evolution.

That's right. Humans evolved in the in in Africa, in the tropics. But, anyway, so we we carefully analyzed all these data, I mean, really carefully analyzed them in terms of calories, in terms of nutrients, in terms of whether the food came from animals or plants, and it was pretty staggering to see that not a single 1 of these diets actually resembled the paleo diet in terms of percentage of fat and carbohydrates, etcetera. But even more interesting was that the diets were so variable. Some of the hunter gatherer populations were pretty much all plant with very little animal food, and some were a lot of animal food, especially marine animal foods and almost no plants, and everything in between.

To me, of course, that's what I expected because humans evolved to eat anything. We're the world's, animal kingdom's ultimate omnivores. We didn't evolve to eat a paleo diet. We evolved to eat a diverse set of paleo diets. Then finally, the paleo diet bans all kinds of foods.

Now, some the bans are quite sensible. You shouldn't add sugar to your food. Junk food is bad, and the paleo diet bans those. So, I'm on board with that. But the paleo diet also bans all legumes.

No beans. No lentils. No chickpeas. All these foods that most people think are health food. No no tofu.

No no peanuts. You know? So peanut butter, which is my favorite food, you know? Totally banned. And then and then it also bans all cereals, all all grains.

So you can't have wheat. Even if it's whole wheat, you can't have brown rice. You can't have quinoa. You can't have any of these things. And and they claim that our ancestors didn't eat these these foods, and that's just not true.

We have archaeological evidence that our ancestors ate ate all of these things, and we even have ethnographic evidence that that hunter gatherers eat these foods. After all, we evolved to eat anything. Anything. You can put it in your mouth. You can digest it.

It's it's what we evolved to do.

1 of the really fascinating points that I remember from that study was there is, of course, this very strong idea that, you know, candy shops did not exist back in the Pleistocene, so, you know, where it's something completely new. Now, of course, that's true. Candy shops did not, but the amount of honey that some of these hunter gatherers consume was just staggering.

I think the Hadza, about 10% of their diet is honey.

That's that's a lot of honey.

Oh, yeah. Well, I've actually gone out with Hadza foragers and seen them. There was 1 morning we went out hunting. Didn't go hunting. I followed them while they went hunting, and they didn't kill anything, But they went from 1 hive to another.

I think they went through 5 hives, smoked out the bees, and ate an ungodly amount of honey. I would have gotten sick from eating that much honey.

Yeah. And, of course, I mean, they are modern day hunter gatherers. They are not our ancestors, but it's it's it would strike me as surprising if that has suddenly changed so much from from the from the good old times. So probably quite a lot of honey in the ancestral diet.

Sure they did. But, you know, I mean, the point is that they they're not eating honey or not eating honey or whatever you may think about honey for the sake of their health. They're doing it because they want food. They want energy, and honey is a very energy rich food. They're And not thinking about whether they're going to get cavities or diabetes.

They're thinking about how to bring home as much food to their families and feed themselves as much as possible.

Well, if we think about what our ancestors did eat, 1 of the things that you mentioned earlier was that there were there's there's a lot of hunter gatherers who don't eat that much meat. It's this, like, extremely meat heavy caveman diet is probably a bit of a myth, but it's not fully a myth, right, in the sense that humans our ancestral diets almost certainly did include some meat. And, your career I mean, the reason I knew your name originally has to do very much with how this came to be, how did hunting become not the only, but a very important part of the way that humans got their food back in the days. So why don't we go briefly into that story?

We started eating meat, we eating our ancestors, at least 2500000 years ago, probably a bit older. You know, exactly when the 1st hunting, 1st scavenging occurred is controversial, but by 2,500,000 ago to 2000000 years ago, it became a regular thing. Certainly, by 2,000,000 ago, early hominins at that time, Homo erectus, probably was hunting large, big animals, the kind of ancestors of kudus and wildebeests and things like that. Of course, that was long before any projectile technology. The bow and arrow wasn't invented for another 2000000 years, and the atlatl and the spear thrower, even spear points were maybe as old as 500,000 years ago.

It's a little bit controversial. None of the technology, the projectile technology that we think about for hunting was invented back then. We think that the major way or a major way they hunted was through persistence hunting in which humans run long distances. You know, you kind of run and then you walk and you track and you chase, and you can basically drive an animal to heat stroke.

And why do we drive the animal to heat stroke, but we don't get the heat stroke?

Because we we are filled with adaptations not only to run long distances very effectively. We have adaptations from our heads to our toes that make us superlative runners. That's why people run marathons and and all that's why I ran 5 miles this morning. But we also have the ability to dump heat unlike any other animal. Sweat.

We have no fur. We have millions of sweat glands unlike the animals that we're chasing. So we can dump heat when it's hot and those animals can't. And an animal especially can't dump heat when it's galloping because it can't pant, which is its major way of dumping heat. So if you can make an animal gallop for a while, it's going to get hot.

Then it'll try to hide and cool down. But if you can track it and chase it again before it's cooled down, a combination of tracking and chasing, running and walking, you can drive an animal to a heat stroke. Recently, a paper was published by some other scientists, not by me, I had nothing to do with it, because we had documented in the ethnographic record a bunch of cases of this. But they found, in just the recent ethnographic record, 400 different cases all over the planet of people doing this.

These are people who also have bows and arrows.

Correct. Yes. So it just shows just how effective a way it is for hunting. Hunting is dangerous. If you get up close to a wildebeest and try to thrust a spear into it, it's going to do everything it can to kill you so you don't kill it.

It's going to gouge you with its horns. It's going to charge you. It's going to kick you.

Unless if it's really tired, I guess.

Unless it's dying, right? This is a way of safely killing an animal effectively and getting meat. It's also important for scavenging because if you want to I've spent a lot of time in Africa. I've driven all over to Serengeti and places like that. Let me tell you, you don't find just dead animals lying around.

When you find a dead animal, it's always surrounded by scavengers. Either the lions are still there or the hyenas are there, the vultures and whatever. If you want to scavenge, you also have to be quick, and that means running.

So you see where the vultures are going and you start running to get there.

Right. We call that power scavenger. So if you can do that in the middle of the day when the hyenas and other scavengers can't get there as quickly as you can, that would have been a huge advantage. I think we 1st evolved to run to scavenge and there was continued selection. Eventually, we started running in order to hunt and we became incredible long distance runners.

How did that shape our bodies? You mentioned that we have a lot of adaptations. Let's not go through the whole list, but

Yeah, you don't want the whole list.

No, I don't, but let's take top 3.

Well, I mean, 1 is the spring in our feet, so the arch in our foot. The longitudinal arch in our foot is a spring for running. You don't need it for walking.

So chimpanzees, they don't

No. No. They have totally flat, flexible feet. Even Lucy didn't have that kind of arch. You know, Australopiths didn't have that arch.

Okay. So the ancient pre Homo ancestors of humans did not really have an arch. We developed the arch around that time when you think that meat eating becomes

important. Arch is from a from a fossil called o h 8. It's about 1,800,000 years old from the bottom of you know? So, yeah, so this evolves around then. The gluteus maximus, so the enlarged gluteus maximus.

So the big butt.

Butts. Exactly. We can see in the fossil record that those enlarged in the genus Homo, and they're used they're used for running, not for walking. A long Achilles tendon in a chimpanzee, it's just a centimeter long and in humans it's 0.5 the length of your tibia. That's a spring for running.

We have head stabilization mechanisms. We have genes like CMAH, which which if you put it in a mouse, it doubles its endurance. We have metabolic adaptations.

And the sweating is is a is a huge thing that you mentioned. But there are some animals like horses who who who are really good also at long distances. Some dogs seem to be pretty good, especially, I guess, in cold. But what's the what's give us a little take on all of that thematic, the other animals that are good at long distances.

So some perisodactyls can can run can sweat a little bit.

Who are they?

Perisodactyls. So animals like horses.

Like horses. Okay. Okay.

Okay. And they they have what's called apocrine sweat. So it's like the sweat that we have in our armpits. Right? It's it's very oily, protein rich sweat, so it's it doesn't it's not as effective for cooling.

And secondly, a horse can only gallop about 20 kilometers before you kill it. So so a horse can run about 0.5 marathon at a at a galloping speed. Oh. It can go farther at a at a trot.

Oh, interesting.

But they but even then, they can overheat. So I actually participated in 1 of these man versus horse races once.

Oh, really? Okay. Okay.

I'm a middle aged Harvard professor. It was over a mountain in Arizona in heat in October. I can't remember the number, but there were like 53 horses and 41 humans. And, I think I beat all but 9 of the horses. Okay.

You know what? Also, the horses had a medical checkup because a horse can die because they can't tell the rider that it's overheating or in cardiovascular distress. They actually have a mandatory veterinary checkup for the horses, which they subtract from the horses' time. We don't the runners, the human runners don't get this. So, actually, I think I probably would have beaten even more horses if they didn't have that

Fascinating. Fascinating. I did not see that coming.

I never won you know, I'm not a great runner. Right? I'm I'm a I'm an okay, you know, middle of the pack marathoner, but I'm so the fact that I could beat most of the horses in that race tells you that, you know, average everyday humans can outrun.

Well, you're not average when it comes to industrial modernity because a lot of us don't run marathons.

Yeah. But it's not just your average horse they just take from a pen. These are horses that have been trained to do these just like the humans. The horses

are trained

with their rut.

That makes sense. That makes a lot of sense. Well, let's let's move on. I mean, we talked about the paleo diet. We talked about honey and now meat and how getting meat, this this fashion of running for the meat probably shaped our bodies in many ways.

But then and there's another thing that probably shaped the early human story a lot that has to do with food which is food processing and cooking. Now cooking with fire, let's talk about that in a moment, but even before we have fire we have other ways to process food, grinding, slicing, etcetera. You, as part of writing this book Fed Up, you did something which really surprised me in a delightful way, which is that you tried all sorts of curious diets for 2 weeks and see what they did to you. What did going on a raw diet teach you about human evolution?

Well, I have to commit that was a bit of a stunt because I sort of know already about raw food diets quite a bit. Raw foodists are people who believe that if you heat your food, you destroy its nutrition. You cause the proteins, like enzymes, etcetera, to be denatured, to break down.

Which on the record, there's not really much evidence for that, right?

Oh, it's nonsense for the most part. I mean, it's true. For some foods, if you cook them, you get less nutrients. But for most foods, cooking actually makes the foods more nutritious because you break down cell walls, you liberate the nutrients in those foods, and also, you spend a lot less energy digesting your food because you've sort of predigested it a little bit, so you get more energy from the food and you spend less energy digesting it. The other thing that was really challenging about the raw food diet is remember, I'm not eating a raw food hunter gatherer diet.

I'm eating a raw food, modern human diet from a very fancy supermarket here in Cambridge, Massachusetts with foods that have been domesticated that are low in fiber. They're extremely rich in nutrients. Even then, we had to spend a ridiculous amount of time processing the food, slicing it, pureeing it, and using a food processor. There are no food processors for any hunter gatherers, I can promise you that. Even then, my wife and I were just constantly hungry.

We were just struggling to get enough energy from these foods because it's hard. It's hard to get enough energy from foods that aren't cooked. There's a reason every society in the world cooks its food. The only people who can get away with a raw food diet are people in places like Cambridge, Massachusetts or Berkeley or wherever, some modern western city where they have access to supermarkets and a lot of food and food processors and all that kind of stuff. And even then, they struggle to get enough energy.

A lot of women who are on raw food diets don't have enough energy to have normal ovarian functions. They don't have normal menstrual cycles. All these folks lose a lot of weight. It's a good weight loss diet. So yeah, it's just tough to Look, we have very small mouths and teeth.

We have small intestines. You know, we just don't even have the anatomy anymore to live without cooking our food.

So in the same way as hunt as as this endurance running shaped our bodies in many ways, in the same way the fact that we started processing our food, probably 1st on a raw food processed diet, no blenders, but stone tools.

Right.

And then later by cooking with fire. I guess that all shaped us in a way in these ways that you mentioned we get we we are able to process food without massive teeth, without massive bellies.

Correct. We did a study that we published in Nature, I think it was 10 years ago now, where we showed that it's just using simple Oldowan tools, the oldest kind of stone tools basically. You just take meat and you cut it up with a stone tool. You end up spending a lot less energy chewing your food. Any fewer chews are required to swallow it, you break the food down into much, much smaller particles, you get more energy from that food.

So we showed that just simple stone tools forget cooking, just simple stone tools are enough to explain how and why in the genus Homo, teeth get smaller, right? So if you look in the mouth of a Homo erectus, its teeth are basically the same as yours and mine. Then maybe just a wee bit bigger, but a dentist wouldn't even notice. Then at some point, humans also started cooking. Of course, with cooking, things really took off.

There's a bit of a debate about exactly what the old is cooking and whether hominins were able to take advantage of brush fires 2000000 years ago. Who cares? The important thing is that by 1000000 years ago, you begin to see a little bit of evidence of fire in the archaeological record. And at 400,000 years ago or so, roughly, give or take some time, it really takes off, right? Everywhere you go, you see evidence for harz and cooking and whatever.

And that was just transformative because not only did it give us a lot more energy from our food, but also it enabled us to eat all kinds of foods that we weren't able to eat before. It expanded the diversity of foods that we could eat, made the foods more nutritious, enabled us to eat foods that we couldn't probably eat before. Just think about meat, right? Like Hadza, maybe 30% of their diet is meat. And they sometimes eat raw food, but by cooking their meat, they make it safer, right?

You're much less likely to get sick from that meat, right? And that saves you from energy. There are all kinds of good things from cooking. And of course, fire has other benefits like, you know, warding off other animals and keep helping you.

Yeah. And and and how much do you think that this is, if not the reason, then the biggest reason for why we have had the capacity to grow such a big brain.

Fire and cooking are clearly part of it. Hunting is also part of it. Look, if you look in the fossil record, brains barely get any bigger from about the very 1st hominins 7000000000 years ago up until the origins of the genus Homo. And then 2000000 years ago about, it's when the curve goes shooting up. Clearly, meat is part of that.

Endurance hunting is part of that. The hunting and gathering system is part of that. Tools are part of that. And then around 304 hundred thousand years ago when cooking becomes really common, that graph just accelerates even higher. It's multiple factors.

There's not ever going be 1 explanation. But to get a big brain, you need a lot of energy because brains are very costly. So, now, our brains are consuming about 20% of our resting metabolic rate. That's a lot of energy. And until we had a lot of energy available to us, we couldn't afford to have selection for bigger brains.

So having more food, better quality food, more energy from our food, and there's lots of reasons for that. Cooperation is 1 of them. Tools are 1 of them. Cooking is 1 of them. Meat is 1 of them.

All of these factors together combined are important.

And so in a way, we we we became this creature that unlike let's say, I I I'm not a chimpanzee expert by any means. My impression is that chimpanzees, they spend quite a lot of time just eating. Yes. And a lot of other apes spent quite a lot of time just eating a pretty monotonous forest diet.

A chimpanzee spends 0.5 its day chewing.

0.5 its day chewing. Wow. And so we become a food processor and a chef. You know, we we we process the food, we cook the food, we become an omnibore that's able to eat all sorts of food, we have all these interesting ways of getting different to eat, catch, prey, which we've now discussed, and that that makes us the kind of creature that eats, I don't know, 3 times a day, something cooked and processed rather than 0.5 of the day, something monotonous from the tree.

We We can eat almost anything. It's amazing. We were able to eat almost anything and almost everywhere by able to disperse out of Africa. Africa itself is incredibly diverse in terms of its habitats. But outside of Africa, even more diversity in its habitats, and hunter gatherers spread all over the planet.

And we're able to eat those incredibly diverse paleo diets that range from all meat to all plants to all everything. You know, by cooking, processing, etcetera, it's extraordinary what humans can and do eat. And that's a result of really this sort of hunting and gathering system and the flexibility it gives us, and that includes food processing.

And food processing is let's we can put a pin there because as the story goes onwards, we will get to industrialization and ultra processed foods, which we'll get to, but let's put a pin there. In some sense, it's interesting to remember that processing itself is not something particularly modern. It's actually very much part of this big story that that that launches us.

Correct. But we've really taken processing to ridiculous heights.

Yeah. Yes. And we will get to that. But before we do, and we before we even talk about the big transformation when farming began way before industrialization, 1 point that I was really surprised to read in your book that at least you linked also to this this brain growth and the fact that this brain is such an energy hungry organ is that humans, you say, are a very fat ape. What does that mean?

So your average mammal has about 5% body fat. Like, you take a chimp and render its fat, it would be, you know, 5% of its body weight would be fat. And that's kind of typical.

Which is funny because they they look at they look chubbier because they have that massive belly that processes all that unprocessed food.

Yeah. That's that's not fat. That's not fat. There are a few animals that have a fair amount of body fat, very rare, like marine mammals, things like that, for insulation. But your typical lean hunter gatherer, a lean male might be 10% to 15% body fat and lean female might be 15% to 20% body fat.

These are skinny people, right? So lean human beings have 3 to 4 times more body fat than our primate relatives. That's because fat plays a really important role in our biology. Fat, 1st of all, helps us pay for our big brains, even if we're in negative energy balance because brains constantly need a lot of energy all the time, ceaselessly. Brains don't store energy, so you need to have a lot of fat, in babies especially.

So when babies are born, 0.5 the body's energy is going just to its brain. It needs a lot of body fat, That's actually why children grow actually, in the 1st year of life, they become even fatter. The average human baby is born at 15% body fat. By a year of age, it's 25% body fat, a healthy, normal baby. That's to make sure it has energy for its brain.

Fat is also necessary like money in the bank for things like nursing. Nursing, producing breast milk, very expensive. Imagine you're a hunter gatherer mother. You're producing breast milk. You're spending hours a day walking around, getting food.

And what if you don't get any food for a few days? You're a negative energy balance, right? You're losing weight. You still need to continue to produce breast milk. Where is that energy going to come from?

It comes from body fat.

And the reason we need that more than chimpanzees who also breastfeed is partially because the brain is such a thirsty organ. Is that right?

Yeah. Exactly. And also, a chimpanzee has 1 offspring at a time, but hunter gatherer mothers tend to have multiple offspring.

Oh, yes. This is a weird thing about humans. Yeah.

So we've our reproductive rate massively. So in order to be physically active, to nurse, to do all these things, you need a lot of body fat because we have such an energetically intensive way of life, energetically intensive body, our metabolisms spend more energy per kilo than chimpanzees. We need more. It's like having more money in the bank. We need to have more energy onboard for when we're not getting enough from our food in order to continue our way of life.

And so humans evolved to have high amounts of body fat.

So interesting. Okay. Well, let's move on in the story. I mean, how much can we say in a on a general level about how much our eating habits, the eating habits of our ancestors change when most of humanity slowly becomes an agricultural creature. We become farmers.

Our ancestors become farmers. Now, because paleo diets, like you said, they they differ. There's not 1 paleo diet, so we cannot tell the story as simply as going from 1 diet to another diet. But is there still something something that we can say in general about how the eating habits of humans change with the advent of farming?

I think people I think there's been exaggeration of how far farming changed people's diets, frankly, because the 1st hunter gatherers just started growing what they hunted and gathered. I mean, it's not that complicated. They couldn't domesticate all the animals that they were hunting, but they certainly started domesticating and growing a lot of the plants that they were gathering. Yes, there was a shift in diet. There's a decrease in diversity.

But when we talk a lot about the problems with modern diets, we blame farming. But I think actually we should blame industrialization more than farming because, for example, early farmers, when they were growing, say, various grains like rye or oats or wheat, example like that, they're not refining them. They're having whole grain cereals, right? They're getting a lot of nutrition from those things. Pretty much every farming culture around the planet figured out how to come up with reasonably nutritious diets.

There's a kind of a formula, right? You have a grain or a cereal, like wheat or it could be rice or it could be corn, and you combine that with a legume. In The Middle East, it would be lentils or chickpeas or some other kind of bean. In Mesoamerica, it's corn and beans. In Asia, it's soy plus rice, for example.

Everywhere you go, you combine a grain and a legume, and guess what you have? You have complementary proteins, You have all the amino acids that you need and a lot of nutrients, calories. Lot Then you also combine that with some vegetables. In different parts of the world, farmers would grow cabbage or we could go on, all the different vegetables that people grow around the planet. You supplement them with nuts and seeds and fruits.

You have some animal products, so you have dairy and, to some extent, some meat products. It could be fish or meat, some combination. Those are the traditional kind of farming diets. Now, the problem with those diets, there are still problems that people can run into. The biggest 1 are famines.

When you're a hunter gatherer, you don't need that much food because have small family sizes, but you also can't get that much food either. Farmers can now, in the same amount of time, get a much, much higher return on what they get, and their families start to get bigger. But guess what? If you have a drought or a fire or a war or something like that, you now have a famine, right? And all of sudden, you start dying like flies, whereas hunter gatherers, when they encounter food shortages, they just move, and they also have fewer mouths to feed, so they're much more mobile.

But if you're a farmer, you're stuck. You're in a village. You can't move to the next place because those people are going to kill you if you move over and try to take over their fields, right? So farmers were able to get a lot more food and have a lot more babies. With farming, you get population growth, but you also get famines.

The other thing that happens with farming is that because you're not moving regularly, you're now in the same place all the time, so you have less hygiene. Right? You're you're now basically, you know, shitting, you know, where you live. Right? Yes.

And and so there's there's sanitation issues.

I've seen this actually interestingly that there's even data on modern day hunter gatherers when they start settling more and more as they pretty much all recently have, that you do start having, like, more parasites. I think Of course. There was some study on the Akita in The Philippines, for example, that these kind of hygiene issues, they really do become a problem immediately when you start becoming a bit more sedentary.

Yeah. The average hunter gatherer moves 7 times a year. Farmers never move, right? But also, you're living with your animals, so now you get all these zoonotic diseases, the diseases that jump from animals to humans. Population densities go up, so you have more disease transmission and higher rates of transmission.

The big problem with farming were famines and infectious disease. And so, you have a lot more babies, but life expectancy decreases, lifespan decreases, healthspan decreases. But I don't think the diets themselves There's evidence that the diets themselves are all that terrible. They're not as diverse as hunter gatherer diets. Think about what's the healthiest diet that experts today tell us to eat.

It's things like the Mediterranean diet. Those are just traditional farming diets. Right? They're not crap food modern diets.

It's I think it's 1 thing to say that we have some relatively healthy traditional farming diets. It's another thing to say that the actual diets eaten by most peasants in history were healthy. And if we mean, for example, I I've covered quite a lot of economic history on the show. Economic historians often construct these kind of consumption baskets of like, what would the average person in Bengal, you know, use their money for? And they look very monotonous.

They look very monotonous.

Sure. The average yeah. So you have to distinguish between what, there are different The Mediterranean diet, there are 2 Mediterranean diets. There's the with a capital M and a capital D, right, which is what various experts have defined as the Mediterranean diet.

Yes.

And then you look around the Mediterranean and you find incredible diversity. Just like there's no 1 paleo diet, there's no 1 Mediterranean diet, right? Of course, within the Mediterranean, there's incredible variation in terms of what people are able to eat based, to a large extent, on socioeconomic status. It's true that peasant diets can be very monotonous. They eat porridge all the time, but you have to remember that the medieval poverty peasant diet is not a stand in for all farming diets.

These are these are impoverished people being manipulated by the feudal system. Their foods are being taken away. They're being forced to grow various things. That's yes, of course, there are peasant diets that are awful, but you have to separate the historical perspective of poverty and socioeconomic stress caused by feudalism and other problems like that with what farmers can and should produce. Look, I work in, for example, that part of Kenya where I work, the Nandi Hills.

People there work hard. They don't have running water. They don't have electricity. But they produce actually a pretty healthy diet. Their problems are not nutritional.

Their problems come from infectious, from malaria and things like that and from the other kind of scourges that occur from poverty, But, you know, they have they have pretty nutritious diets actually.

Well, the good I think we can then move towards what you already mentioned very many times as a problem in your opinion. Let's start with just the problems in industrial diets. We can get back to whether there are some bright sides, but let's just start with the problems and ultra processed foods get a lot of bad press nowadays for I think for many reasons that you also mentioned in your book. Instead of just listing them all, is there 1, 2, max, 3 kind of underlying issues that really drive all these scattered problem findings?

Every time you try to oversimplify a problem, you run into trouble. I think some of the skepticism about ultra processed foods is again a result of oversimplification because the triscuits I ate, there's a kind of cracker that I've had in my house. They're just made from wheat and yeast and water, but they're made in a factory. I couldn't make them at home. Is that an ultra processed food or the frozen pizza that has 800 ingredients and all kinds of crazy stuff in it.

There's no 1 agreement on how to define ultra processed foods, but in general, there are 3 issues that we tend to think about for these foods. The 1st is that they tend to be junk food. Food. They tend to have a lot of calories from added saturated fats and added sugar with all the nutrients removed, so the fiber has been removed. They're using refined grains and refined cereals so that the the protein is gone, the nutrients are gone, the vitamins are gone, the fiber is gone.

So either you are eating the right amount of calories and getting too little of the other stuff, or you're getting right amount of the other stuff and getting way too many calories.

Yeah. So that's 1 issue. Another is that they're designed to be hyperpalatable. So these foods are designed to addict us. There are all kinds of studies on this.

Many of them look, if I take a food and I put too much fat in it, it's kind of disgusting. It's greasy. It's kind of overpowering. Nobody likes overly fatty things, right? Or if I take another food and I put too much sugar in it, it's cloying.

It's just ridiculous, right? Nobody wants to eat that much of it or too salty, But the food companies have figured out that if you have a huge amount of fat and a lot of sugar and a lot of salt, they balance each other out and you get this thing called the bliss point. They actually call it the bliss point, And it lights up our brains and we get addicted to it. And in fact, I point out in the book, you know, there's only 1 natural food in the world that is high in both sugar and fat. Do you remember what that is?

Yes. Milk.

Correct. Yeah, milk. Your mother's milk when you were an infant. High in sugar and fat. And now, we create foods that are like our mother's milk and we go crazy for them.

They're full of energy and we crave them. The food companies know this, so they create all these wonderful foods I'm being a little sarcastic that are cleverly designed to get us to eat as much as possible. That's the 2nd issue. We eat too much. There are studies that are called cafeteria diets where you put people in a room with home cooked foods versus ultra processed foods, people eat a lot more of the ultra processed foods.

We know what happens when you put people in a room with this stuff.

Even if you would have the exact same nutritional profiles, you just end up eating more.

Correct. Yeah, that's been tested. We have experimental data to prove that. And then finally, the final issue is that these things have all kinds of additives and chemicals. There are stabilizers and emulsifiers and preservatives and colorants and flavorings and all kinds of stuff in there.

There are all these chemicals in the food, and we have no clue what a lot of them do. Some of them, we do have a clue and we know that they're problematic. 1 that bothers me or concerns me a lot is maltodextrin, which is a kind of stabilizer and emulsifier that they put in a lot of processed foods. It's a form of sugar. It quickly becomes glucose and raises your blood sugar levels, but you can't taste it.

You have actually no taste sensation from this stuff, but it's ruinous for your metabolism. It causes spikes in your blood sugar level, which aren't really good. When I see maltodextrin in a food, I just put it back. For me, that's like the canary in the coal mine, and it means that this is a crap food that I have no interest in buying because I have no idea what it's going do to my digestive system. So, you combine all the added sugars and fats in the salt, you combine the addictive nature of these foods, and you combine the additives, you've got a triple whammy of bad things.

And the result is that, look, I was born in 1964. When I was born, about 10 percent of Americans were classified as obese. In my lifetime, that has quadrupled, right? And what's changed? It's the processed foods because now, if I walk into this There's a supermarket just a few blocks away from me.

When I walk into that supermarket, there are about 40,000 foods in that supermarket, 40,000 different products, which is very impressive. Somewhere between 5070% of those products are ultra processed. That's the food system that we confront. In study after study after study, there are clear associations between the consumption of these foods and and people's health outcomes. And and, you know, we need to do something about this if we want to help each other live happier, healthier lives.

And I guess 1 of the things you say we should do is not figure out a very fancy new do exactly this kind of a diet, but rather back to basics, eat a lot of plants, not necessarily only plants, but, you know, fresh plants are a good thing.

It's not too complicated. Look, in England, I don't know if that what you have in Finland, but in England, there are just like green, yellow, and red labels on food. It just helps people figure out, you know, if it's a red label, maybe you should not be eating this. A green label is probably very healthy. A yellow label, be careful.

We don't have anything like that in United States, it's 1 of the reasons why. Of course, England is struggling too, but we need to give people information to help them just because the world is going to still have processed food. We have 8,000,000,000 people on the planet. We can't feed them all without processing food, but we can certainly have healthier processed foods. That's a social political issue.

So then a little bit of a pushback. I don't know how much I don't know what would be the right way to formulate this, but let's put it this way. If we think of the current food system we have let's forget everything about ecology for now just because this that's a whole other episode. But let's if we just think about health, how healthy the food is that we eat. Now, there is an obvious way, you've just explained, way in which the current kind of industrialized food system will have certain kind of problems.

A lot of those problems are very accentuated in The U. S, but you do find them a little bit everywhere nowadays. And the problems are clear and you can see them in things like not only obesity, but also type 2 diabetes. A lot of this has to do with those things you just talked about, you know, too many calories in, too little fiber, etcetera. But for most of human history, my understanding is that the biggest problem with food is that there hasn't been enough.

There you mentioned famines earlier with farmers. My understanding is that with hunter gatherers also, it would be a little bit too romantic, too nostalgic to say that they didn't have famines. Yes, they could move around, but I'm you correct me if I'm wrong, but my understanding is that there probably has been seasonal all sorts of seasonal stressors also for the hunter gatherer diet. And if we look at what's happened during the past, if we look at the really big picture of what's happened in the past 150 or so during the kind of boom of industrialization in the food system, this has been a remarkable era of where, for example, people's heights have gone up everywhere around the world. Famines have gotten less less and less common.

Even in the poorest places in the world, people are now much taller than they were 150 years ago. Is there a case to be made that we paid a pretty high price for this, but this is a little bit like Churchill's democracy, you know? It's the worst system except for all the other ones we've tried.

This is the standard argument that you hear in medicine today that aren't we lucky now to have this modern world in which we get to live long enough so that we can die of heart disease instead of smallpox? So let's go through your logic 1st. The 1st is it's true that hunter gatherers go through food shortages, but nothing like farmers. If you're a hunter gatherer and we know this from ethnographic studies, when they're struggling and there's not enough food, guess what they do? They just pick up and they move.

They're not nailed to 1 place. Hunter gatherers live in very low population densities and they're in very, very large areas. They're much less territorial, and they have much better ability to cope with seasonal and annual variations in food because they eat hundreds, if not thousands, of different kinds of foods. They have animals available to them. They can be much more flexible.

So, the evidence is that famines and food shortages are probably an order, if not 2 orders of magnitude worse with farming than hunting and gathering. That's 1st. 2nd, it is true that the modern world has enabled us to have more energy. I mean, factory farming and factory foods make available a lot more energy than before. Furthermore, today, the reason that people's height has shot up is not because of the amount of food we have.

It's actually because of sanitation and and other things which have decreased infectious diseases.

And by the way, I just you can continue just very briefly. I've seen people who try to tease apart how much is it because of, for example, food versus sanitation. We don't have the answer to that, but I do think that it's both based on most models.

Well, Chris, it's both, but it's energy, but but there's no question that life expectancy really shut up when you have with sanitation. You look at graphs of life expectancy. And furthermore, again, food is a manager a manager of energy. And so, more food has really enabled people to to to be be taught. But you stop growing when you're 20.

And what is it the food that the food is killing us now? They don't kill us Our diets aren't killing us when we're young and growing. Our diets are killing us when we're 50, 60, or 70 and getting diabetes and heart disease and cancer. So your height is not really relevant to the kinds of chronic diseases that are killing us today. So, the question is, is the tradeoff that we have today essentially a necessary result of our industrial system?

The answer is absolutely not. If we were able to change the way in which we process food and provide people with healthier foods, we would have a lot fewer chronic diseases in the world today.

You mentioned earlier, of course, many times being overweight, being obese. This is something that a lot of people struggle with and would like to find better tools for. But instead of making this a how to lose weight teaser here from Daniel Lieberman, I thought that maybe we could talk about something which is actually more universal, which is how to maintain weight. Because even for people who are not overweight, they would probably want to maintain their healthy weight. And I've also understood that actually dieting often fails in not in the fact that you couldn't drop some kilos, but actually it's just that you can drop them, but it's very normal then to just get them back very soon afterwards.

So maintaining weight seems to be in some sense maybe what we should really be focusing on. It's maybe doesn't get quite as much attention as it should. And 1 thing that you mentioned a couple of times both in your book and some of the other interviews I've heard from you is that exercise is probably a a decent way of losing kilos, but it's exceptionally good at maintaining the healthy level of weight that you've gained. Do I get that right? And if so, why?

Well, 1st, let's talk about exercise and weight loss because that's a bit of a contentious issue. A lot of people, when they think about exercise and weight, they think about just calories, how many calories you spend. And so, like this morning, I ran about 8 or 9 kilometers and I probably spent about 400 or 500 calories. The breakfast that I ate when I got home had the same amount of energy easily, if not more. You have to really exercise an enormous amount and eat very little afterwards in order to lose weight.

You can do it, but you can't lose it quickly and you can't lose a lot. However, study after study has shown that moderate amounts of exercise are very effective for helping people prevent weight gain. Now, 1 reason is because you're spending some energy. But even more importantly is that when you exercise at moderate amounts, 1st of all, doesn't make you very hungry. If go for a walk for 0.5 an hour or so, you don't come back ravenous.

Yeah. I think this is really good news, by the way, that these studies don't say go run a marathon or find No.

You don't need to run marathon. Just walk an hour a day and you're in great shape. Secondly, and probably more importantly, we don't understand all the mechanisms and there's is that when you are physically active, you actually change your hormonal response to food.

Interesting.

So if I a piece of bread and I've not been exercising for several days, the glucose in that bread goes into my bloodstream. My sugar levels blood sugar levels go up, and then my insulin levels go up, and that insulin basically stores fat. And furthermore, insulin causes you to hold on to that fat too. But guess what? If I if I walk an hour a day, forget the calories I spend walking, the insulin rise from eating that piece of bread is much lower.

The result explains the data, which is that people who get about 300 minutes of exercise a week, which is 40 minutes a day or so, tend not to gain weight or they're much less likely to gain weight. 1 of the reasons that weight has been going up around the world is that people are being less physically active. There are studies. For example, there's a study I love to cite because it's done here in Boston. Right?

So we have a stereotype of overweight policemen who eat a lot of donuts. Right? Yes. If you watch The Simpsons, you'll see the stereotypists, they have a lot of fun with the stereotypes. So, there's a study done here in Boston on policemen.

They had a bunch of overweight, donut eating policemen who put them on a diet. It was a serious 16 week diet. All of them did the diet, but some of them exercised while on the diet. Guess what? The ones who exercised and dieted lost a little bit more weight than the ones who just dieted, but everybody lost a lot of weight.

Then afterwards, the ones who were prescribed exercise, who stayed and kept exercising, they kept the weight off. But the ones who stopped exercising when the diet was over, their weight went right back

up. Interesting.

And you know, it's a classic example of how physical activity prevents weight gain and it also prevents weight regain.

Another thing that inspired me about benefits of of exercise is that even for someone who, for example, does struggle with too much weight, 1 of the things that they struggle often is having too much sugar in in the blood or having issues with insulin in the long run. I mean, is why type 2 diabetes is often associated with being overweight. And 1 of the really good news here is that even if the weight wouldn't change at all, just using muscles, doing any kind of exercise is a way of mitigating some of those problems. For example, the muscles literally suck sugar out of the blood. Right?

Oh, it's huge. The yeah. Effects are normal. That's what we're talking about with the endocrine effects. So when you exercise, for example, you produce more of what's called GLUT4 transporters in your muscles.

Those are the transporters that take glucose out of your bloodstream so you improve your metabolic health. When you exercise, you increase the number of mitochondria and you keep your mitochondria more healthy. I mean, are many, many, many, many things going on when you exercise that improve your metabolism. I was just mentioning only just 1 earlier.

So basically, even if you would see an article saying exercise does not help you lose weight, it's not a reason not to exercise. There are plenty of reasons.

Oh, that's just nonsense. It's complete, utter, total nonsense. 1st of all, exercise does help you lose weight. Just how it doesn't help you lose a lot of weight fast. Secondly, exercise improves your metabolism and it helps prevent Penta from gaining weight.

It also has manifold other health benefits. Nobody you know, why we talk about diet versus exercise is to me part of the madness of the modern scientific way of thinking about these things.

But when thinking about this from an evolutionary point of view, you also often I've heard you, not only in your books, but also in your interviews, bring up a kind of compassionate message that these things in some sense, it is a should. Yes. We should do this differently, but there is something that you understood from studying human evolution that really says that both dieting and doing exercise, these are actually really hard things. Like, it's it's natural to not want to do them right.

Oh, we never evolved to exercise. We never evolved to diet. We never look. I can Look, when people are confused about what to eat because think about it, we evolved to know how to get our food. We never evolved to choose our food.

Hunter gatherers have to know a lot in order to hunt animals and find their plants and process them. Farmers have to know a lot to grow their food. You walk into a supermarket with 40,000 different foods. How are you supposed to decide what to choose? We were never evolved to cope with that kind of diversity and abundance.

And guess what? We go for the stuff that lights up our brains. And if you have trouble in a supermarket, that means you're normal. Right? I have trouble in a supermarket.

If you have to go to a restaurant, are all these incredible foods available for you, and you struggle to choose the healthy option, that's because you're absolutely normal. We also never evolved to lose weight. If you're struggling to lose weight, it's because we never evolved to diet. Evolved to have fat, but we never evolved to get rid of the excess fat. In fact, we have all these adaptations that work against us and keep us holding onto it.

And if you think exercise is difficult, well, we never evolved to do unnecessary, unrewarding exercise. When you go to a supermarket or an airport or whatever and there's an escalator next to a stairway, everybody takes the escalator. Even though there were no escalators in the Paleolithic, it's because we evolved to take it easy whenever possible. And then we tell people they're lazy because they don't want to exercise. Well, nobody exercised until recently.

Nobody got on treadmills or went to a gym and lifted weights because they had to work very hard and otherwise, they took it easy because they were struggling to get enough energy. So, we've created a modern world that makes it hard for us to choose our food and hard for us to stay physically active. And then we blame people because they make the wrong choices and we blame people because they struggle to do unnecessary, unrewarding physical activity. It's totally unfair. An evolutionary perspective, I think, helps us recognize that most of us, the reason that people struggle is it's through no fault of their own.

It's because the environment that they're in has had forced them to do things that they never evolved to do in the 1st place and that require serious willpower that's very hard to overcome.

If you could go to any period in history, any region in history, and for a year, you would be just there eating there. What would you like to try?

I'm not very good at questions like that. I mean, I'm like I'm no I'm not different from anybody else. I I have to tell you, I'm a I'm a bit of a Francophile, and I love good French food. I love Italian food, and I enjoy going to restaurants like that.

But not to the paleolithic? You wouldn't wanna go to, like

Oh, absolutely not. No. No. I mean, I'd be curious to see what life looked like, but I'm quite happy to live today. Look, I'm a I'm a middle class person, but today I can eat better than, you know, the kings and queens of of of of the yore.

I mean, I have access to incredible health care. Not doctor Pangloss. I don't think this is the best of all possible worlds, but but it's incredible what we have available to us.

What's the most important or interesting or inspiring thing that we haven't talked about today?

The reason I wrote Fed Up is that there's a lot to talk about. As we said earlier, our ancestors had to know a lot in order to get their food, I think today we need to know a lot to choose our food. But we're not taught it, right? I don't know about Finland, but in America, not even physicians, doctors don't get taught much nutrition. They don't get taught much about exercise because they're trained to treat symptoms of diseases once they occur rather than to treat their causes.

And so, when we go into a store and there's 1 of those labels that tells us how much fat and polyunsaturated fat and this, that, and other nutrition labels on our food, don't teach in school. Again, I don't know about Finland, but we don't teach in school what people need to know in order to help them figure out what they should eat. The knowledge isn't that abstruse. It's not that hard.

Though there are pretty controversial claims about any of those, right? Maybe that's the problem.

Well, some of them are controversial, but they needn't be controversial. Some of the controversy is just nonsense, right? Like the carnivore diet people claiming that you're better off eating all meat. I mean, that's just silly. I know I'm going to get some hate mail from this, but it's counterfactual.

There's always a grain of truth. Yes, you can survive for a long time on meat and meat is nutritious, But is an all meat diet better than a diet that has lots of plants? No, it isn't. But there are people out there who desperately want to think that way and so that's become controversial. But it shouldn't be controversial, right?

But there's actually not that much controversy among nutritional experts. I think most of them would agree that a Mediterranean type diet has the best evidence for it. It doesn't have to be exactly Mediterranean. You know, there are variations, like a Nordic diet or a traditional Asian diet or traditional Mesoamerican diet, etcetera, etcetera. I think most people agree that too much saturated fat is never good for you.

I mean, how bad for you is a bit of a controversy, But but the evidence is clear. You're always better off having an unsaturated fat compared to a saturated fat.

So more olive oil, less butter.

I don't think there's any controversy over fiber. Fiber is good for you, and you should have plenty of it.

And we process a lot of fiber out of our food because of the industrial processing we discussed.

Right. But there's a few, you know, there's a few crackpots out there who think you shouldn't have any fiber, but they're crackpots. Yeah. I think pretty much everybody agrees that too much sugar is bad for you. I think pretty much everybody agrees that ultra processed foods are bad for you.

I think pretty much everybody agrees that, nuts are good for you and olive oil is good for you, etcetera. Honestly, there's not that much debate about what's a healthy diet. It's just turned into a lot of nonsense by TikTok and influencers. It's not that complicated, but we still need to inform ourselves so we can figure out how to deal with what's happening. So to go back to my original point, why is it that we, in school, when we teach chemistry, for example I don't remember when you studied chemistry.

The chemistry that we learned in school had nothing to do with nutrition. But why not, when we teach about hydrogen bonds, teach people about the differences between a saturated fat versus an unsaturated fat? We never discussed any of this when I took chemistry in high school. I had a wonderful high school chemistry teacher and I loved chemistry in school, but we never learned anything that was practical. Why don't we teach, when we teach chemistry, teach nutrition?

I took biology. None of the biology I took in school taught us anything about health, right? And I think we can and should teach people this information. We don't and we now treat it as if it's abstruse and controversial. Most of it's not that controversial and most of it's not that abstruse.

So what I tried to do in Fed Up is provide in 1 book what I think I could be wrong, what I think everybody should know, and I tried to make it entertaining, tell lots of stories, and give an evolution framework. And so I think that's the most important thing.

And it is a very, very entertaining book, and you do actually try these different diets for 2 weeks, which adds a lot of flavor into the text. Thank you for writing it. Before we end, my final question is always the same, which is how has all your work shaped your outlook on humanity?

You know, I I'm very lucky. I get to travel around the world and and work with people who live very different lives than me. And, you know, the more I study and spend time with people in different parts of the world, the more I realize that, you know, most people just want the same thing. They care about their families and their loved ones, and they're working hard to survive, and they're doing their best under difficult circumstances. And I think that we're much more like each other than we're different from each other.

But what's really different is the opportunities that we have. And and I think, unfortunately, the the inequity in the world right now is just really it's heartbreaking. And so, yeah, that's a so, you know but basically, you scratch the surface, we're all basically the same.

Daniel Lieberman, thank you so much for all of your work and your time today.

My pleasure.

Okay. So that was it for today. Thank you so much for sticking with us until the very If you want more material on human evolution, there is plenty in the archives including the whole origins of humankind series in the spring 20 25. And if you're interested in the relationship between food processing and our brain growth, then do find the episode with Susana Herculano, Josel, that launched the Brain Science series a year ago. And as always, if you want to show the show some support, 3 easy things you can do.

Give the show 5 stars if you think that it deserves it, share it with a friend or on social media, and you can always, of course, jump on the Patreon wagon and make a monthly donation to the show at patreon.com/onhumans. That's it for today. Until next time. Take care.