From paleo to intermittent fasting: are any diets actually good for us?

0:00This is The Guardian.

0:11What should we eat? It's a simple enough question, but as the options multiply, the answer feels more and more confusing. From vegan to paleo, low-carb to low-fat, each attracts its own bunch of evangelical devotees, all claiming that the science is on their side. But can one diet really act as a magic bullet for health, weight loss and longevity? And can our distant ancestors' diets offer any clues? Today I'm speaking to evolutionary anthropologist Professor Daniel Lieberman. From The Guardian, I'm Ian Sample and this is Science Weekly.

1:03Daniel Lieberman, you're an evolutionary anthropologist and professor of biological sciences at Harvard University. Now, usually you study the evolution of human physical activity, but for your new book, Fed Up, you've turned your attention to food. Why? Well, it's the next thing, you know, I mean, I can't tell you how many people ask me, you know, What's more important, diet or exercise? And the answer is both, obviously. And I teach physiology at Harvard, and I teach nutrition. And just like everybody else, I'm confused about the whole diet world out there. And I wrote it partly because it's sort of a sequel to my last book, Exercise, but also from my own curiosity, I want to evaluate all the different evidence out there about diets and think about it from an evolutionary perspective.

1:49To test some of these diets, you and your very patient wife, Tonya, tried each one for two weeks at a time. I'm going to ask you about some diet myths, starting with this idea that to be healthy, we all need to eat like early humans. People have heard this called the paleo diet. But remind us, what does that actually involve eating? So the paleo diet, like all diets, it has a germ of a good idea, right? which is that obviously we're adapted to certain foods and we're not adapted to other foods. And so the idea behind the paleo diet is that we should eat like our ancestors because presumably we're adapted to eat that way.

2:26But in general, it's a high-protein diet that bans junk food. That's good. But it also completely bans legumes, so no beans, no lentils. You're not allowed to have any grains, so no wheat, no oatmeal, no rice, even if it's brown rice or whole grain food. And you're not allowed to eat any dairy, so there's a lot of elimination. So some aspects of the diet are pretty good. Some aspects I have some serious problems with. And people might expect you to be kind of all for this kind of diet. You've spent time with hunter-gatherer communities. You've eaten with them. But I'm interested in how much that sort of paleo diet does resemble what our sort of paleolithic ancestors would have been eating.

3:08Well, that's one of the big problems. So the idea that our ancestors never ate grains or beans is just silly. It's just wrong. I mean, we have lots of evidence from the archaeological. I mean, we have even starch granules on the teeth of Neanderthals and things like that. In my lab, actually, we've done some analyses. We've studied all the diets of all the major hunter-gatherer groups in the tropics for which there's good data. And you name it, they ate it. I mean, we evolved to eat anything, not for the sake of health, but in order to have as many babies as possible. and if it can crawl or fly or swim if it grows and won't kill you immediately our ancestors ate it and as you're saying like the paleo diet encourages people to avoid something which i know is a staple food for you and that's peanuts almost every episode we do here on the podcast on on health seems to end up with us telling people to eat more legumes so why the hate for them from the paleo people?

4:08I mean, or do we need to stop shilling for big bean or whatever? So part of the paleo diet elimination of legumes of beans and peanuts and things like that is that there was this mistaken idea that our ancestors didn't eat them. It's actually, there's a bean called the marama bean, for example. It's the number two food in the Kalahari desert among the hunter-gatherers there. But the other reason that they eliminate them is because they claim to contain anti-nutrients. So these are compounds that like lectins or oxalates or phytates, you may have heard of them, that bind to minerals and vitamins and prevent them from crossing into our bloodstream.

4:45So that's bad, right? So you think, okay, God, the paleo diet's got it right. Let's get rid of these things. But the problem is that when you cook your beans, you get rid of those anti-nutrients or you reduce them to harmless quantities. Otherwise, vegetarians and people around the world would be dying of malnutrition from eating these foods that almost everybody else considers to be a health food. Given all those issues, I did wonder why the paleo diet has been so successful, why it's been so popular. I think there's two reasons. The first is that it does have a grain of truth. There are foods that we're poorly adapted to.

5:20We are not adapted to eating a lot of refined cereals. Sugar, white flour, all those things in great quantities do cause harm. The original paleo diet told people to eat not too much saturated fat, and that was actually pretty sensible. There's also a problem with this, you know, what we call the naturalistic fallacy, the idea that if our ancestors did it, it must be good for us. If our ancestors didn't do it, it must be bad for us, you know, this kind of Rousseauian idea. And if that were the case, you know, we shouldn't sleep on mattresses, we shouldn't take showers, we shouldn't brush our teeth, you know, we shouldn't use antibiotics or refrigerators.

5:54I mean, it doesn't take a lot of brain power to realize that this way of thinking takes you only so far.

6:06You mentioned saturated fat, and that was another diet myth I wanted to ask you about, is this idea that, you know, saturated fat can be seen as the sort of root of all evil when it comes to health. Can you give me a bit of history on that? Gosh, yeah. If there's any one thing that's still debated a lot in the nutrition world, as saturated fat. I mean, it's, of all the parts of the book, that was the part that I, I sweated over the most and consulted the most experts and, and there's still not complete unanimity. So here's my take on saturated fat. So saturated fats are mostly animal fats, right?

6:38These are, you know, things like butter and cheese and meat, et cetera, are rich in them. Coconuts also have them. And some people actually handle saturated fat better than others. It turns out there's a lot of genetic variation, but here's the thing. Study after study, after study after study shows that unsaturated fats, both monounsaturated fats like olive oil and polyunsaturated fats, that's like as rapeseed oil or what we call canola oil in the United States, those, you always do better on those. There's no question about it. So I think about, remember Blaise Pascal, the famous philosopher who said, look, we don't really know if there's a God, right?

7:14But if you're not sure, you're better off believing in God because if there is one, you're going to be better off in the afterlife, right? And I think the same is true. I mean, I don't want to be sacrilegious, but I don't want to, you know, I think the same is true of saturated fat. Look, saturated fat might not be your foe, but unsaturated fats are always your friend. And so if you want to hedge your bets and avoid the risk of heart disease, always, always prefer a plant fat over an animal fat. So the olive oil wager as opposed to Pascal's, right? If you fast forward to today, the US Health Secretary is telling people, you know, you need to be eating way more saturated fat.

7:52And, you know, so what is the evidence on that? Basically, none. I, you know, there's a lot of loony stuff going on at the moment. And look, there's part of this is because there's a lot of skepticism about science. And one of the reasons that people are skeptical about saturated fat is that back in the 70s, the war on fat was raging, right? There's a famous physiologist named Ansel Keys, who was largely responsible for this. And he was absolutely sure that saturated fat caused heart disease. And that's just spread around the United States. But what happened was that a lot of people swapped, you know, if you don't eat something, you eat something else.

8:29And what people ended up eating was a lot of carbs. And the big food companies jumped into the fray, right? And they figured out this is a way to make a ton of money. So they started making a lot of ultra-processed foods with refined carbs and lots of added sugar and added plant fats, et cetera. You know, this is the low fat movement. And guess what? People got fat. They started, you know, eating a lot more of this junk food. And that, I think, bred a lot of skepticism. Given that that one around saturated fat is so hard to unpick, where do you think people should come down? I mean, you're talking about, you know, Pascal and so on.

9:01And is it that you say, well, look, it may be pretty bad. So So maybe your focus should be on these unsaturated fats or what? Well, I would say, look, that saturated fat is probably not as bad as we were told, but it's not your friend. There's no evidence that saturated fat makes you healthy. And whereas there is abundant evidence that if people who replace saturated fat with unsaturated fats, either mono or poly, do better. They have lower rates of heart disease. They have lower rates of cancer. They have lower rates of Alzheimer's. They have lower rates of all kinds of chronic diseases that are associated with diet.

9:37Now, that doesn't mean you should, like, eliminate, you know, butter and cheese from your diet. In fact, there's some evidence that dairy is pretty good, you know. I had yogurt for breakfast this morning. I mean, I don't eliminate these things. I just don't eat a ton of it.

9:53Coming up, the one diet that Daniel does recommend.

10:05There's another belief out there, another common belief in the sort of diet world, people who sort of talk and think about these things, that breakfast is the most important meal of the day. And I guess that went out the window when you tried intermittent fasting. How did that go? How did you find intermittent fasting? It's a very interesting debate going on right now, or not debate, but a set of ideas. Some diets try to restrict calories by restricting how much you eat. And intermittent fasting works by restricting when you eat. And so there are different kinds. There's like what's called the 5-2 diet, where you eat five days a week, you eat normally, and two days a week, you basically starve yourself.

10:40And I wasn't going to do that. So I tried the most popular form, which is to eat within an eight-hour window, which basically means skipping breakfast and not eating a late dinner and not snacking. And that's not very hard, to be honest. There's no question that our bodies evolved to go through periods of eating and digesting food. We call that positive energy balance. and then retrieving that energy from our bodies to use it, to burn it as fuel. And that's called negative energy balance. And we have obviously evolved to go through these cycles of positive and negative energy balance. And it turns out that that kind of what's called metabolic switching turns out to have all kinds of benefits for cells throughout the body.

11:19The evidence isn't huge, but there's growing evidence that going hungry occasionally can be metabolically very beneficial. and so you know we don't really know yet how useful that can be for your health but it's it's a reasonable hypothesis 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 in um and did you look at sort of the evidence for the claims made around longevity and so on which i guess may be a bit trickier because as you say well what are we going to do follow humans until they're 80 or 90.

11:56Yeah, 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, they will live longer. There's no evidence that doing that for humans has any benefits whatsoever. And in fact, there was a study, a very famous study done on primates. There was a bunch of macaques in a lab and they gave half the macaques a kind of what's called an ad libitum diet. They could eat whatever they wanted. And the other macaques were restricted in their calories. And it was reported that the calorie restricted macaques did way better in terms of their health and lived longer.

12:36For the intermittent fasting and calorie restriction. Turns out though, when you looked at the data that the ad libitum macaques were basically fed a crap diet with lots of sugar and cereal and all that. And they were getting obese and they were getting diabetes and whatever. This is not a normal macaque diet. So at incredible expense, the National Institute of Health redid the experiment, took another 20 years. I mean, this is, I can't imagine how much money this took. And this time they gave the macaques exactly the same food, but just restricted one set of macaques. And the calorie restricted macaques did not do any better whatsoever than the normally fed macaques.

13:11So look, there's all these diets out there that try to come up with a hook. You know, the blue zones diet claims that if you, if you eat like these people, you'll live to be a hundred. And first of all, these people are not calorie restricting themselves. And then secondly, the evidence that they're living to be 100 is completely overblown. By the end of the book, you've tried everything from meat-only, pretty much diets, to veggie-only diets, everything in between. Has anything stuck? Has anything become the new Daniel Lieberman way? Of all the diets that I tried, the one I enjoyed the most, partly because it's the most familiar to me, but also it's a cuisine, it's not a diet, is the Mediterranean diet.

13:50And surprise, surprise, it's the diet for which we have the most evidence. There's a little Eurocentrism here because, you know, we study European diets more than say Asian diets or Mesoamerican diets or et cetera. But, you know, there are so many studies which show that people on a Mediterranean sort of style diet, and that's capital M, capital D, you know, it's not necessarily what everybody in the Mediterranean eats, but it's sort of an idealized version of it. You know, lots of olive oil, lots of whole grains, not too much meat, fish, etc. The evidence is overwhelming that those people are much less likely to gain too much weight.

14:23They have lower rates of heart disease. They have lower rates of cancer. They have lower rates of all kinds of other chronic diseases. If you had to pick from scientific evidence one diet out there, it's a no-brainer. I was interested that you end the book by saying that we all need to eat more like the fox and less like the hedgehog. People listening to that might be wondering, what on earth are you talking about? Take me through that. Sure. So there's a scrap of poetry from the 7th century BC by a poet named Archilogos of Paris. And he apparently wrote, the fox knows many things, but the hedgehog knows one big thing.

15:01What we think he meant was that, you know, foxes, when you chase a fox, they'll do anything to escape. You know, they'll run, they'll hide, they'll whatever. Whereas if you chase a hedgehog, what does it do? It rolls into a ball, right? And so hedgehogs just have one big idea. You know, they try to, you know, and in diet, that's like, you'd be low fat or low calorie or low carb or raw or paleo or whatever. Whereas foxes see that there's complexity and there's trade-offs. Every time you eat something, you don't eat something else. Something that might be good for you in terms of your heart might be bad for you in terms of, I don't know, your metabolism.

15:34I mean, who knows, right? So foxes see that there's no simple magic bullet solution. And I think the problem, the confusion that a lot of people have about diet is that we've been sold by a lot of hedgehog diet promoters these magic bullet diets that supposedly help us live to be 100 and will optimize our health. If there's any word I become to detest, it's the word optimize because it doesn't work that way. And it's great marketing, but it's scientifically very problematic. And elimination is a classic hedgehog scheme. You'll be perfectly fine if you never eat a grain or never eat a legume or carnivore diet.

16:14It's believed you should never let a plant pass your lips or I could go on. Right. And elimination rarely works. And moderation is obviously much more sensible as to quote or paraphrase Epicurus. You know, practice moderation so you can enjoy the pleasures of life in abundance. Well, Daniel, thank you for helping us navigate it all and for writing the book. It's my pleasure. And, you know, I hope that help the book can help people. Thanks again to Professor Daniel Lieberman. You can order Fed Up, what evolution reveals about food, diet, health and eating well from The Guardian Bookshop. Just search guardianbookshop.com.

16:58And that's all from us This episode was produced by Josh and Chana The sound design was by Joel Cox And the executive producer was Ellie Bury We'll be back on Thursday See you then

17:16This is The Guardian

17:23Thank you.