What evolution reveals about eating, dieting and fat

**SPEAKER_1** (0:00)
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**Terry Gross** (0:18)
This is Fresh Air. I'm Terry Gross. Whether you want to lose weight or just eat healthy, it's sometimes confusing to know what to eat. There's a lot of contradictory advice and diets that are the opposite of other diets. Do you want to go low fat, high carbs or low carbs, high fat? Do you want to be vegan or eat mostly meat? How about the paleo diet and eat like our distant ancestors? How much salt should you eat? There's contradictory advice about that too.
If you're trying to lose weight, should you consider GLP-1s? What do we know about the possible side effects? To make sense of all of this, it's helpful to know something about how our digestive systems evolved in ways that make some foods harmful and make it difficult to lose weight and challenging to keep it off. My guest Daniel Lieberman studies how evolution has affected our digestive system and the amount of exercise we get and need. He's a professor at Harvard and founding chair of its Department of Human Evolutionary Biology. His new book is titled Fed Up, What Evolution Reveals About Food, Diet, Health, and Eating Well. As part of his research, he and his wife tried many diets each for two weeks to see how their bodies, minds, and appetites responded.
Over the years, as a paleoanthropologist, his research has taken him to the Arctic, Africa, and Latin America to study the activities and diets of indigenous people in remote villages with no electricity or running water, and see how their bodies compare to Americans today.
Daniel Lieberman, welcome back to Fresh Air.

**Daniel Lieberman** (1:55)
I'm pleased to be here.

**Terry Gross** (1:56)
So you tried several different diets, each for two weeks, to see how you responded, just to get a sense of what they're like before writing about them. Of course, you couldn't figure out the long-term effects or how much weight you'd lose, but you got a sense of how your body responded, and how your appetite responded, and you recruited your wife to do this with you.
What was the worst diet that you tried that was just too difficult? Let's exclude here the first diet that you mentioned in the book, which was a diet that our ancestors used before they learned how to make a fire and actually cook. Because that sounded so horrible that you gave up within a few days. You didn't last the two weeks.

**Daniel Lieberman** (2:42)
Yeah. The raw food diet was by far the worst. I think my wife lasted three days and I lasted four days.
That was just really rough. I think the next diet I didn't like the most was, I wouldn't say, it's probably a toss up between, well, no, actually, I'm sorry. I know the answer. That would be the meal replacement diet. Because I picked diets that sort of corresponded to the period of the evolutionary history of food and diet. And for the beginning of the industrial era, I thought, well, what's more industrial than a meal replacement diet? And so I decided to replace my breakfast and lunch, but not dinner, because there was no way I was going to do that, with one of these milkshake things, which has all the nutrients that a human being supposedly needs. And after a day or two, it became a form of torture because I missed food. They're just kind of gloppy milkshake-like concoctions that are very nutritious but very unsatisfying.

**Terry Gross** (3:44)
And how about an actual food diet that you tried?

**Daniel Lieberman** (3:48)
I would say it was a toss-up between the Atkins diet, which I found, I just missed plants, you know. I mean, I just missed eating, you know, carbohydrates.

**Terry Gross** (3:57)
What's in the Atkins diet?

**Daniel Lieberman** (3:58)
So the Atkins diet is a high-fat diet, a high-protein, high-fat diet with very few carbohydrates. And you're kind of limited to like a little bit of broccoli on your plate. That's basically it. But no bread, no pasta, no rice, no crackers, no... I mean, the list goes on of carbohydrates that you basically cannot eat. You can only eat very low-carb plant foods. And that got really, really wearing. I mean, it was really tough.
I like my carbs. And I also found it frustrating because I think that if you have carbohydrates that are not refined, the whole wheat products, brown rice instead of white rice, I think they're pretty healthy actually. So I missed those. And then the other diet, I think that I, maybe it's a toss up that I found very challenging was the Paleo diet because the Paleo diet bans all legumes. So no peanuts, no beans, no soybeans, no tofu, no all these things. And I love those. And also no cereals, no grains. So that was also challenging.