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Recently, thousands of attendees around the world gathered in Austin TX for Paleo FX, the largest conference in the world  for supporters of a stone age menu. The premise of the popular Paleo diet is that if we would mimic the eating habits of our paleolithic predecessors, we would be healthier, less obese, and avoid ailments big and small. Conditions including anxiety, asthma, certain cancers, depression, Type 2 diabetes, high blood pressure, irritable bowel syndrome, and osteoporosis.

Today’s guest, Daniel Lieberman has studied extensively the habits of our ancestors. He’s a Harvard evolutionary biologist who has focused his research on  the human body and how it has evolved over millions of years. His book, The Story Of The Human Body: Evolution, Health and Disease, examines the increasing disparity between the needs of our Stone Age bodies and the realities of the modern world. So even though we’re living longer, we’re living with chronic disease. 

I first heard about Daniel when his study of endurance running made the cover of the prestigious journal Nature under the title “Born to Run” and led to him being a major figure in the bestselling book with the same title, “Born To Run”. In running circles, Daniel has been known as the “barefoot running professor.” And even though you might be saying, “Ouch!” You’ll want to hear why it might be important to give your feet a break from your daily shoe habit.

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Kathy Smith:                                     Hi Daniel. Welcome to the show.

Daniel Lieberman:                   Thank you.

Kathy Smith:                   So the premise that if we stick to the foods of our hunter gatherer ancestors and what they used to eat that we can avoid diseases such as the heart disease, the high blood pressure, the diabetes and cancer. Is it true that we’ve evolved to eat a meat-centric diet?

Daniel Lieberman:                   In a word, no. Look, I have a lot of sympathy for some of the ideas that paleo diet folks advocate, but I think there are a number of concerns that I and others have with both the details but also the logic of that argument.

So if we go to, for example, the topic of meat. Although it is true, our ancestors did eat meat, they didn’t eat a huge amount of meat. It depends of course of where you look at which hunter gatherers you look at. But the estimates for most tropical hunter gatherers range between 20 and 30% of their diet comes from meat. Very rarely more. It’s only in places like the arctic where there’s nothing else to eat that the quantity of meat goes up.

But there’s an even more serious issue and that is–and it’s really at the heart of this topic, which is that fundamental assumption about the paleo diet is that if we ate like our ancestors, we would be healthy. And the problem with that assumption is that we didn’t evolve necessarily to be healthy. Just because our ancestors ate something doesn’t mean it is necessarily good for his health, because what natural selection cares about is one thing and one thing only and that’s reproductive success. So a better way of saying it is that we evolved to healthy insofar as health improves our reproductive success.

Kathy Smith:                   So the idea that we want to be living longer and we’re focusing on longevity is actually not exactly the way that we were designed as you mentioned. That we were just designed to reproduce. And it’s interesting because I was in the Galapagos Islands with my family. And when I was down there, I was reading a book, Beak of the Finch. And they were trying to mimic the evolutionary studies of Darwin. And what I found fascinating when I was reading the book, is that as much as we think of evolution as something that occurs over millions of years, our bodies are evolving all the time. And yet, to your point, to continue the species, we have to have more children, we have to appropriate and have more children. We don’t necessarily have to live to be 100.

And so, I do see that the dieting focus is all about that we would start to jump into a diet and many times, we don’t know the long-term effects of these diets. But what I also find fascinating about your book is that you talk about there’s not one paleo diet. Can you explain that?

Daniel Lieberman:                   Okay, well, you said a lot. So there’s a lot to unpack there. But I agree with you about there not being one paleo diet. I mean, there are many problems with the paleo diet movement. One of them as you just mentioned is that there is no one paleo diet, right. Do you pick the diet that the Hadza, who are in the Tanzania, eat, who have become a sort of hunter gatherers du jour or the San of the Kalahari or the Inuit or the Natufians in the Middle East or Native Americans in the New World? There is incredible variation from region to region in terms of what diets are in terms of modern hunter gatherers. And then if you go look in the past, there are other diets because our ancestors used to be chimpanzees. Should we eat like chimpanzees or should we eat like Neanderthals or homo erectus?

So the idea that there is a paleo diet is kind of laughable. There isn’t. Humans evolved to eat a wide range of foods in a wide range of habitats under difficult conditions. And they did so not in order to be healthy but in order to have as many offspring as possible.

Now that doesn’t mean that we aren’t less adapted for certain foods. There’s no question that we never evolved the ability to handle high amounts of sugar, we never evolved the ability to handle high amounts of food that was low in fiber, we never evolved the ability to digest trans fats. So there’s no question that some of the foods that in some aspects of the modern diet unquestionably lead to ill health, and we call those mismatched conditions. And that’s largely what my book is about. It’s about mismatched conditions.

But from the same token, it doesn’t mean that if you just somehow imagine that there was one paleo diet, which there wasn’t. But even if there were that that diet wouldn’t necessarily be optimal for health and longevity.

Kathy Smith:                   Okay so, when it comes to farming, let’s just talk about how farming enters into this. So when you talk about paleo, from what I’ve read, we’re talking millions of years ago and then agriculture was introduced about 10,000 years ago. And so how have our bodies adapted to things that we farm? Because I think that’s one of the things that gets thrown out when it comes to the paleo movement.

Daniel Lieberman:                   Well, yeah. Paleo folks seem to think that anything that’s post-agricultural is verboten. But obviously, there’s been selections since agriculture. The most famous example, the best studied example is lactose persistence. So about a third of the world continues to produce genes for the enzyme that digests the major sugar in milk, lactose. So that’s one example. There are all kinds of other genes that have been selected for the last 10/12,000 years in certain populations that help with digestion of carbohydrate diets. So evolution didn’t stop in the Paleolithic. It’s still going on today. That said, the rate at which environmental change is happening today is so much faster than evolution can act that that’s really where we’re getting into trouble.

But yes, you identified another kind of flaw with the paleo diet. You could go on to others. For example, the paleo diet for some reason forbids legumes. I find it preposterous to think that our ancestors didn’t eat legumes occasionally or that beans or lentils and all those sorts of things are somehow unhealthy. The paleo diet forbids dairy. Well, my ancestors went through selection to eat dairy. Again, that’s just even the question of what my ancestors ate. It’s another question as to whether or not what they ate was actually beneficial for their health or not. Those are two separate questions.

Kathy Smith:                   So it seems like there’s some foggy logic to some of the premises. But what about this idea of being genetically predisposed to a certain kind of diet? I know that I wrote a book once called Getting Better All the Time. And it had three separate diets. I worked with a nutritionist from UCLA. And part of the book is that we found that certain people just work better more plant based. Other people can have a little bit more meat. Myself, I work better with a little bit more fish. Is there something to be said if we’re genetically coded for our diets?

Daniel Lieberman:                   Well certainly, there’s been selection in different populations to handle different kinds of diets. A very famous study that came out a few years ago on enzymes that desaturate certain kinds of fats found that this particular enzyme is produced very strongly in Inuit populations for example. So there’s no question that certain populations have adaptations which may be beneficial for certain diets. The problem is that we understand so superficially most of the genetic basis for differences between humans’ diet. I would be very, very, very hesitant to make prescriptions about what people should eat based on what population they come from or even what genes you identify. Because we still don’t understand the vast majority of the genetic basis for variations in digestion.

And remember that so much of what goes on, it’s not just in our genes, it’s also our microbiomes and the organisms that we have within us. And those are another ecological community that’s also evolving, and so we have to take that into account as well. And we are far from understanding those interactions as well. I think we have to be very hesitant before making confident prescriptions at the moment.

Kathy Smith:                   Okay, if you don’t mind me asking, what about you? With all of the studying that you’ve done, what kind of diet do you follow? I know you’re a runner. I know you’re very active. But is there a particular diet that you–?

Daniel Lieberman:                   I pretty much would be–most people would call a Mediterranean diet. I eat a lot of fruit and vegetables and fish. And I almost never eat red meat. But I don’t pay huge amounts of attention. I eat lots of nuts. But I run a lot so I eat a lot. Yeah, I would say a Mediterranean diet is probably what I eat most of the time.

Kathy Smith:                   Yeah, so do I. But let me–you mentioned running so let’s switch gears. I am running a half marathon in–

Daniel Lieberman:                   Wait. We do need to talk about saturated fat though.

Kathy Smith:                   Okay. Go back.

Daniel Lieberman:                   Because that is such a–it’s become almost like a dogma in the paleo world, and it’s like almost you’re a heretic if you have concerns about saturated fat. And I have to say that of all the things about the paleo diet, it’s the refusal to look at the data on saturated fat. There’s been kind of this pendulum swing. We were told by Ancel Keys and others back in the day that saturated fat was bad for us, then there was a little questioning of that.

But the more good careful studies come up, the more we realize that you have to be really careful about the data that you look at. And a very, very, very thoughtful analysis was just published by the American Heart Association by [Sacks et al], which I urge anybody interested in research stuff to read, that looked at saturated fat and not just how much people eat but what they replaced it with. And when you replace saturated fat with carbohydrates, there is no difference in mortality and morbidity rates in terms of how much saturated fat you eat.

But when you replace saturated fat with polyunsaturated fats, both Omega 3s as well as Omega 6s–and paleo diet folks tend to vilify Omega 6 fatty acids. There’s a huge difference. So we need to be really, really careful before we again start prescribing people with diets that we don’t totally understand. And the dictum that you should go ahead and eat as much saturated fat as you want concerns me.

Kathy Smith:                   So this idea of eat as much butter or coconut oil, palm oil, the type of things that have become very popular recently could have a very adverse effect on our bodies. I have to tell you, I experienced it first hand, because I would say maybe three years ago when I started listening to some of these principles and following them and putting a little bit of whatever in my tea in the morning and not being as concerned about some of the saturated fats. I have heart disease in my family. My dad died of a heart attack when he was 42. And I noticed my cholesterol levels went up dramatically in six months after being on that type of diet which I quickly reversed. But yeah, I do think that it’s good to hear about this information that’s come out. Can you repeat, again, what the study is?

Daniel Lieberman:                   Oh, it was recently published in the American Heart Association Journal–and I can pull up their [unclear 00:17:03] in just a second–by Sacks et al in 2018. It’s a very large and thoughtful med analysis and I can get you the reference in just a second.

Kathy Smith:                   Okay. Good to know. Thanks for bringing that up. But yeah, I wanted to touch on fat because, of course, that is a big part of the paleo movement.

Okay, switching gears. Running – I am running this half marathon. I have run one marathon in my life as I mentioned. As I talked to you earlier–or sent you an email–that I have a daughter who’s an Olympic runner, who competed in Rio in 2016. And part of this idea of what we put on our feet to run has been very interesting to me. The book Born to Run where we learned about the Taramuhara Indians and how they don’t wear shoes. And you just started a whole movement with your barefoot running. Can you talk about the impact of shoes – the positive and negative impact of shoes – when we work out, when we exercise and when we walk?

Daniel Lieberman:                   Well, let me just backtrack just a few seconds. So it is true that I’ve done research on the Taramuhara Indians as well as I’ve done a lot of work in Africa. But I did not write the book Born to Run. I wrote a paper entitled “Born to Run”. And the book Born to Run, I think it has a lot of things wrong. For example, it is not true that the Taramuhara go barefoot. The Taramuhara, for the most part, wear minimal shoes.

And secondly, you get the impression from reading the book Born to Run that the Taramuhara all run around constantly and they’re all getting out of bed and basically running ultra-marathons. And nothing could be farther from the truth.

So I have actually some concerns about that book. And the book, more or less, promotes the idea that if you somehow get rid of your shoes, everything will be better and that you’ll have no problems. And that’s just not true. And I think a lot of people probably got injured because of the book because it has that air of truthiness. It sounds like what you want to believe rather than what necessarily be true.

The fact of the matter is that shoes like everything else in the world, including what we eat has a costs and benefits, right? There are benefits to shoes. They protect your feet but they also cost. The decrease sensory input from the ground. And we all basically make trade-offs all the time. So there are good things about shoes and there are bad things about shoes.

But the one thing that shoes do do that we have shown is that when people run with shoes versus without shoes, especially shoes that are very cushioned, they run in a different way. They tend to land on their heel. Whereas when people are barefoot or sometimes but not necessarily when wearing minimal shoes, they’re more likely to land on the ball of their foot, what we call a forefoot strike. And those have very different characteristics in terms of how the body interacts with the ground and the kind of shockwave that gets sent up the body. That may be very important in terms of injury.

Kathy Smith:                   So I know when you have a cushy shoe on, that idea that you can land on the heel, there’s almost this idea that you land there and you’re being protected because of all that cushion there. But the idea is – and since I have switched my running style to where I’m landing on the front of my foot, I feel much less pressure and impact in my hamstrings and my glutes.

Daniel Lieberman:                   That’s correct. It’s a much less impact in every way. Of course, it makes sense. If you were to take anybody’s shoes off and have them run down a hard surface like a road, they would immediately stop landing on their heels because it hurts. Running is jumping from one leg to the other. If you were to get up and jump right now, you would land on the ball of your foot. It’s not normal to land on your heel when you jump. And the only way in which people do land on their heel when they’re jumping – and running is, again, as I said a form of jumping – is if they have all this cushioning under their heel that it slows the rate of loading.

But ultimately, you still have that very heavy impact; you just can’t feel it because the shoe–it’s not really cushioning it. It’s slowing the rate of loading. So the shoe doesn’t get rid of the energy. It just slows the rate of loading by making that collision occur over a longer period of time. And so you have a trade-off between the rate of loading. So how fast your body comes to a dead stop with what’s called the impulse, which is technically the area under the curb. But the impulse is essentially the total amount of energy delivered. So when you’re landing on your heel on a cushy shoe, you are essentially slowing the rate at which the loading of your foot occurs, but you’re increasing the total amount of energy that’s delivered.

And we don’t totally understand yet what that trade off means in terms of injury. But there’s a reasonable amount of evidence to suggest that those impacts may be implicated in a variety of injuries, from shin splints to possibly even joint disease. And really that’s the subject of a lot of research at the moment.

Kathy Smith:                   So one other aspect of your evolutionary approach to activities is on this idea of being physically inactive. And you wrote somewhere–I read somewhere that you said that we’ve evolved to be lazy. First of all, is that true. And if so, what do you mean by that?

Daniel Lieberman:                   A basic principle of evolution is that you can only spend a calorie once, right? I can spend a calorie either on growing my body, taking care of my body, or reproducing. And what does natural selection really care about? Ultimately, it only cares about reproduction. So if I can divert energy towards reproduction from something else, I win from an evolutionary perspective. And so for millions of years, it was, from a selective perspective, disadvantageous to spend extra energy or unnecessary energy on physical activity. Because you’re taking away energy that can go towards reproduction.

And so when people go up to a staircase that’s next to an escalator and they take the escalator–now, obviously there were no escalators in the Paleolithic, but their instincts are still responding to something very basic and ancient which is that if you can save energy, you should. If you ever go and hang out with hunter gatherers or people who are energy limited, they don’t go for jogs in the morning. The don’t do unnecessary physical activity. They conserve their energy for when they need it, because they have to work very hard in order to survive or moderately hard to survive. And any extra energy they don’t spend on physical activity benefits their reproductive success.

So it makes sense from an evolutionary perspective, and we also know from abundant studies that humans have a tendency to avoid unnecessary physical activity. We call that laziness today. But actually, it’s just being normal. And then we make people feel bad for simply being normal. And that’s one of the problems with the way in which we deal with physical activity. We shame people and blame people for not wanting to exercise. But let’s face it; exercise is a very bazaar and modern phenomenon that we never evolved to do.

Kathy Smith:                   And yet necessary because of the nature of how we do live our life. We no longer are out there chasing antelopes or walking or doing hard, physical labor.

Daniel Lieberman:                   Correct.

Kathy Smith:                   So we had to create the way to move and make it fun, and it became my entire career of putting some music to some movement and getting people to get out there and move a little bit.

So what would you say or what is your prediction, in the sense, of where all this is going? If you had a magic ball or a crystal ball and you could look down 20, 30, 40, 100 years from now the way that we are sitting and we’re not using our bodies in the way that our ancestors did, what could be some possible evolutionary changes if this continues?

Daniel Lieberman:                   You’re right. We’ve had to create novel ways to get people to move because we no longer have to move. And you’re also quite right that the best way to get people to move is to make it fun. And the sad fact of the matter is that a lot of people have lost the pleasure and the joy in being physically active. And that’s I really don’t like the term “exercise” as medicine. Because we don’t think of medicine as being fun. It’s like something you have to take or you have to do in order to not to die. And that seems like a depressing way to think about it.

But in terms of the crystal ball question, we know it’s happening. More and more of the world is becoming physically inactive, and as the result, more and more people are getting chronic diseases. And as development spreads across the globe, we see this is happening around the world. Type 2 diabetes is the fastest growing disease in the world. What’s happened in the United States is now happening rapidly in China, India, Brazil, and other places.

So unfortunately, the crystal ball is not cloudy. We can see where we’re headed. And the problem is that most of the diseases that people get as a result of physical inactivity don’t really afflict us until we’re middle aged or even older. So diabetes, certain forms of cancer, osteoporosis, or heart disease, these are all diseases that people get after they’ve reproduced. So selection is silent in this regard, because there’s no selective force acting on people’s bodies in terms of these diseases. So they’re going unchecked and they’re rising in rate. So we’re at a period where there’s some data that suggests that actually people being born today in America are actually going to live slightly shorter and less healthy lives than their parents. We’ve reversed the progress that we’ve made over many generations. And the concern is that that’s spreading around the world.

Now, I think this is setting in motion a new evolutionary phenomenon. That’s sort of the argument of my book, The Story of the Body. I call it disevolution, because what we do is we treat the symptoms of these diseases rather than their causes. By doing so, we enable to disease to continue to exist, but we kind of learn to cope with them to some extent.

And that means that the prediction is that these diseases are going to become more common, and more severe, and more prevalent, and we will spend more and more of our time just treating their symptoms and that’s kind of a perverse, modern feedback loop that’s very concerning. It not only causes misery, and pain, and all kinds of problems – mental and physical – but it’s also very expensive. We spend in the United States approximately almost a third of our gross national product on healthcare and for diseases, 75% of which are preventable. And we spend approximately 3% to less than 5% – the estimates vary – on prevention. So it’s just insane what we’re doing.

Kathy Smith:                   Okay. It is so true. And as we know, we have a crisis going on now just with insurance and in the medical community because of the rising rates of all these diseases. But to kind of loop around, because I know that I could talk with you forever. But we do have to wrap it up. And to try to wrap up on a more positive note. If the best thing somebody could do based on your research and not specifically with exactly what kind of diet but what would be, I would say, three or four things that you would say – do this like our ancestors did and you’ll be less likely to get some of the diseases we were just talking about. What would be your bullet points?

Daniel Lieberman:                   It’s a no-brainer. I don’t think there’s any debate. We know that if you want to be healthier and, for that matter, happier, eat less sugar, eat more foods with natural fiber in them – so your fruits and vegetables, don’t go crazy eating saturated fat, don’t smoke, don’t drink too much, and get plenty of physical activity. That’s it.

Kathy Smith:                                     Love it.

Daniel Lieberman:                   Your grandmother knew this. Nobody doesn’t know this. The problem is not what to do. Everybody knows that. Well, maybe with a few exceptions – people who think you should eat as much saturated fat as possible. But pretty much everybody knows that.

The problem is that we live in a world where we are surrounded by options that challenge those ideas. Because our instincts to have sugar, our instincts to have energy-rich foods, our instincts to be physically inactive are deep and ancient. And our ancestors never evolved to have to make the kinds of choices that we make today.

Our ancestors didn’t have to choose to take the elevator or the stairs. Our ancestors didn’t have to choose not to eat the cake that was sitting out there at the lunch counter. Our ancestors didn’t have to decide not to drink the Coca Cola. And so we’re asking people to make choices that, frankly, we never evolved to make. And they’re very hard to make. You have to turn off your fast brain and turn on your slow brain in order to make those choices, and that’s not easy.

So we need to help people help themselves. And that means that we have to create environments, with people’s cooperation, that help them do what they would like to do in the first place.

Kathy Smith:                   Okay, well, I know that this is going to help people out there make some choices just because I believe information is power. And I do think that people get confused, and as much as you say it’s simple, the feedback that I get is that it’s not so simple.

Yes, a few of the things about sugar and such and such, but when it comes to exercise, they’re being bombarded with this exercise is better than this and this will do such and such. And when it comes to diets, I can have a paleo doctor on – that paleo is the greatest and then, I can have a vegan doctor on – that vegan’s the best. People out in the world are getting bombarded with all this information. So I do believe that simplifying it is really important. And Michael Pollan has a line that I quote sometimes, and he says, to your point–let me just think. I have to quote it.

Daniel Lieberman:                   “Eat food, must eat vegetables, not too much.”

Kathy Smith:                   Yeah, you got it. Thank you. It’s those simple sort of things that really help people say, “Okay, it’s not as complicated as you think,” And to your point, your grandmother knew this, her grandmother knew it. Just kind of get back to basics. And the marketers of the world and the hypesters of the world, kind of look twice before you jump in.

Daniel Lieberman:                   Let’s just say, you’re point about people being confused is absolutely correct. And one of the reasons people are confused is that there are a lot of people out there who are trying to make money off particular, untested, or poorly tested ideas.

And I think everybody needs to be a skeptic. You should be a skeptic about almost everything. And when somebody tells you a particular diet works better, you shouldn’t ask first of all, is the diet better but you should ask actually what happens when you’re off the diet. You should also, in terms of physical activity and exercise, if anybody tells you that there’s a best fitness activity or a best exercise is off their rocker. We’re constantly trying to sell people on these ideas that there’s an optimal this and an optimal that. That’s not how evolution works, it’s not how our bodies work. Everything involves trade-offs.

If anybody every tells you that there’s some perfect solution, you know that they’re spouting something insalubrious. There is no such thing as a free lunch. Everything involves trade-offs with no exception.

Kathy Smith:                   So true. Well, Daniel, thank you so much. This is such a pleasure, such an honor to have you on the show, and I appreciate you taking your time. I know it’s valuable.

Daniel Lieberman:                   No, my pleasure. Thanks so much.

Kathy Smith:                                     Nice talking to you. Bye-bye now.