And so what is it about the environment? Is it the ultra processed food? Is it just the fact that we've got all kinds of ways to throw down 3000 calories by rolling down our window at fast food restaurants?

Look, everything about our bodies is an interaction between our genes and our environment.

Everything, right? And this is no exception.

But as you say, our genes haven't changed that much in the last few generations.

But in my lifetime, the percentage of Americans with obesity has quadrupled.

So obviously it's not because some genes for weight gain have suddenly swept through the population in the last generation or two.

But it is true that some people have more proclivity than others.

I would love to hear some of the concerns and or limitations that we are seeing.

Let's talk about the paleo diet and a study you and your colleagues did at the start of the COVID pandemic

pandemicYeah, that was actually one of the starting points for the book because, uh, yeah, during COVID the lab was closed and I had an undergraduate in my lab who was going to do an experimental project, and of course she couldn't do it, so we thought, "Okay, let's scour the literature and find all the highest quality data on what tropical hunter-gatherers eat." So we decided to focus on tropical hunter-gatherers because that was the vast majority of hunter-gatherers, and compare that to the paleo diet, because the paleo diet has some very detailed prescriptions about what you should eat supposedly based on what hunter-gatherers eat.

And it was based on this famous atlas by a guy named Murdock who sort of tried to put together all the data on hunter-gatherers, but it... a lot of the data aren't very good.

So we thought, "Let's just focus on the high-quality data." And, and it turns out there are 12 different populations for which their data are good enough that we can actually say something real.

You know, these are when people actually studied and measured and quantified what it is that people actually ate.

And what we discovered was that, first of all, not a single one of the, of the hunter-gatherer diets actually resembled the paleo diet in any way.

Um, and furthermore, even more importantly, they were all over the place.

Yeah, what do we eat?

But then why does it taste so good?

Well, look, you're pointing out what is unquestionably the biggest challenge today, which is we don't know exactly why ultra-processed foods are really bad for us, because there are probably a number of factors, and what makes them bad for you might not be exactly the same thing as bad for me, but there's some qualities.

The first is that Look, they're designed to be really appealing, just as you said, right? Companies have figured out how to light up our brains.

You know, if you take a food and you put a huge amount of fat in it, it's disgusting, right? Or too much sugar, it's cloying, right? But you put the same amount of fat and sugar and you combine them, bam, it's like, it just turns us on, right? And then you add salt, you better, right? So they've actually...

intentionally engineered these foods to hit what's called the bliss point, right? That our brains just go wild.

And experiments show that if you just give nutrition-identical foods, but you kind of have these foods that are, you know, diets, but you have these ultra-processed foods versus just sort of normal foods, we tend to overeat those ultra-processed foods, right? So they are appealing.

Secondly, they're lacking fiber, which is really good for us, because fiber makes food go rancid, right? So you don't want fiber in your food.

So you hear all of these different things, but

So there do seem to be some health benefits from doing that sort of intermittent fasting, where you're compressing the sort of time period during which you're eating and, um, and did you look at sort of the evidence for the claims made around longevity and so on, which I guess are maybe a bit trickier because, as you say, well, what are we gonna do, follow humans until they're eighty or ninety?

Yeah.

It's really hard to do this, right? And some of the claims about longevity and calorie restriction are overblown.

I'll just put it that way.

So if you starve a mouse or a fruit fly or, you know, certain worms, uh, they will live longer.

There's no evidence that [chuckles] doing that for humans has any benefits whatsoever.

And in fact, there was a study, a very famous study done on, on primates.

So take me through that.

I think this is interesting for people and can really help them kind of process what we're talking about on this podcast.

Yeah, so this is really kind of the framing of the book.

So I start out with two points.

First is that we never evolved to ask the question, what should I eat? You just eat what you have for most of human history.

There were no supermarkets, right? But then the second thing is when you're trying to decide what should I eat, there are sort of two kind of opposite ways of thinking about it.

And the metaphor I use is from a fragment of poetry from 7th century BC by a guy named Archilogos of Paris.

And he wrote, the fox knows many things, but the hedgehog knows one big thing.

They were very popular not long ago and probably still are in some places.

And what is the role of fiber in this equation?

Oh, gosh, fiber does so many things.

I mean, fiber, the more we study fiber, the more we're learning about just how important it is in our diet.

So fiber are carbohydrates that technically we can't digest, like the plant walls, you know, all the things in plants, like grass.

Grass is full of fiber, right? But that fiber does many things in our digestive system.

So one of them is that it, so when food is, once it leaves your stomach, we call that chyme.

C-H-Y-M-E, it's not yet poop, right? Poop is when it finally leaves your body.

And it just feels like we're always jumping into these fantastical ideas around all of these approaches.

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 meat.

At least two and a half million years ago, probably a bit older, exactly when the first hunting, first scavenging occurred is controversial.

But by two and a half million years ago to two million years ago, it became a regular thing.

And certainly by two million years 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.

And of course, that was long before any projectile technology.

The bow and arrow wasn't invented for another two million years, and the atlatl, and the spear thrower, and even spear points were maybe as old as 500,000 years ago.

But is there still something that we can say in general about how the eating habits of humans change with the advent of farming?

... people believe the paleo diet should be?

I mean, God only knows what the hell the paleo diet is.

It's, it's based on, um...

From my understanding, it was based on there's a thing called the Ethnographic Ax- A- Atlas by a guy named Mur- Murdock.

And, uh, I think, um, what they did is they kind of looked at the Ethnographic Ax- A- Atlas, did some statistical manipulations with the diet, with the data there, most of the data aren't really very good, and then came up with some kind of, uh, percentages of what they thought a true paleo diet was.

Um, we actually published a paper in the American Journal of Clinical Nutrition a few years ago, um, where we analyzed all the really high quality diets of hunter-gatherers from the tropics and compared them to the paleo diet.

Turns out none of them [laughs] are like the paleo diet.

But how would you, in a nutshell advise somebody to eat more like a fox with perhaps like explicit principles or pointers?

Describe the Mediterranean diet.

Well, the Mediterranean diet is, is, uh, you know, there's, there's, there's two Mediterranean diets.

There's the, there's the Mediterranean diet with a capital M, capital D that has been defined by, by nutritionists, [laughs] and then there's the Mediterranean diet that people in the Mediterranean sort of actually eat.

And, of course, the latter is extremely variable and, and, um, and hard to characterize very simply.

But, but the, but the Mediterranean diet with capital D, um, is essentially, uh, a diet that's based on whole grains, so, um, often with sourdough, for example, uh, plus legumes.

So you'd have, uh, think about you might have pasta or you might have, uh, bread or something like that or, uh, with, with, uh Chickpeas or lentils or, you know, some kind of legume or bean like that, plus lots of vegetables and fruits, plus moderate amounts of, of dairy, so some cheese.

Um, uh, you pri- prioritize, uh, fish over really fatty meats, but you do eat meat occasionally, just not, not all the time.

So tell us about why or how evolution has made dieting so difficult.

But the general rules of nutrition, of like what the human body needs to function and stay healthy, uh, uh, do they vary that much from person to person?

Not too much, no. Um, what you need, though, isn't necessarily what's best for your long-term health, right? I mean, what...

People can survive on 100% meat diet.

The only food you actually [laughs] need to eat, apart from some vitamins and minerals is meat, is protein, right? Uh, well, you don't, you don't need to get protein from meat.

You can get protein from plants.

But, but protein is the only nutrient you actually have to ingest.

You can, you could technically survive without eating carbohydrates, and you could technically survive without eating, um, without eating fats.

So given all you've said about this, a person listening thinking, "Yeah, well, I, I get that, but w- what do I do?" I mean, in a practical way, what is the information you've just given us, what do I do with it, and how do I move forward?

I mean, the consensus seems to be that for a while at least, meat and fats and limited carbs and leafy greens, they've got enough nutrition to get you by.

Oh, yes.

No, I mean, meat is incredibly nutritious.

You can live for a long time on an all-meat diet.

And ketosis is just when you're burning fat, not carbs, can have benefits.

And we're adapted for that, right? But I just don't know of any evidence that we're adapted to be in ketosis for 24-7, right, all the time.

The evidence really is that it's good to kind of cycle in and out and in and out.

Do you have a simple rule of thumb about fats?

Why do you think it does show up in mice?

Because mice have totally different l- uh, life histories.

So life history is the series of stages that you go through, how you use energy to grow up, reproduce, and, and whatever.

And, and you know, a typical mouse is ready to reproduce after three months, you know, and it has series of babies, et cetera, et cetera.

Mice have totally different metabolisms and different growth trajectories and diff- different d- uh, microbiomes and different, you know, than, than humans.

So, so yes, it is true that, uh, uh, for some species, for some, um, mouse lines, but not all, caloric restriction has been shown to improve their lifespan, but not all of them, by the way.

Um, certainly true for yeast, certainly true for fruit flies, but the evidence for humans is so far mixed.

Hmm.

What is your verdict on this?

[chuckles] Well, again, the calories in, calories out is a-- is another classic example of an oversimplification, right? And again, all these diets, the problem with them is that they're oversimple.

Yes, it's true that we end up balancing calories in versus calories out.

We are, we are subject to the laws of thermodynamics just like every other creature.

But two things.

First is our bodies don't treat all foods the same because we have these things called hormones that allocate energy for-- and change how our bodies digest and, and, and, and move nutrients or-- and energy around our body, which is one of the reasons why carbohydrates have different effects, say, on our fat storage, for example, than, than, say, fats or proteins.

We can get to that later on.

Has the way we sleep changed from the way in which we evolved? And could these sleep patterns have any effect on, like, the patterns in, in the way in which we eat?

Yet at the same time, it's not necessarily something that we have evolved to want to do.

Oh, I would say we didn't evolve to do it at all.

But yeah, that paradox is what really motivated my last book, Exercise.

And maybe to answer your question, I'll give an anecdote, right? I was in Mexico doing some research.

And we were studying runners and people who run and actually discovered that most of the Tarahumara famous for running don't actually run very much.

But anyway, there was this one elder fellow who was a famous runner, did these very long distance races.

And I was being a good anthropologist and I was asking all kinds of questions.

That's a byproduct of doing what they need to do in order to survive, right? So it's It's a side effect.

They say it's really bad for your knees.

Oh, man, that gets me so mad, right? I mean, I hear this from doctors all the time, right? "Oh, yeah, running is bad for your knees." Now, it is true that knee injuries are the most common running injuries.

Um, um, but arthritis, which is really what they're usually talking about, um, it's absolutely definitively not true that running increases rates of knee, uh, cartilage damage and arthritis.

So, arthritis is caused by cartilage wearing away in a joint, right? And it's- it's a- it's a myth that, uh, c- running actually increases car- cartilage damage.

If you have arthritis, running is excruciating and problematic.

But if you don't have it, running actually, uh, if anything, may be slightly preventive, um, because cartilage joints, like everything else, benefits from being used, right? And so physical activity actually helps promote strong and healthy joints.

We used to think that it just caused them to wear away, but actually...

I don't know what to believe anymore.