The Best Diet: Eat Like Our Ancestors
By now, we all know that most of America is fat. But Deirdre Barrett, a psychologist with Cambridge Health Alliance and a professor at Harvard Medical School, says the reasons for this—and how to change it—may come as a surprise. In Waistland, she lays out the science behind the obesity epidemic and shatters some of the myths that she says are standing in the way of really shaping up.
What gave you the idea for the book?
I work in a behavioral medical setting, so I'm very interested in what people need to do in a practical sense. The major impetus was that I didn't like what any of the other books out there were saying. There's so much bad advice, even in otherwise solid books.
And one of those pieces of bad advice is that if we just listened to our bodies, we'd naturally crave healthy food?
It's counter to biology. That myth is so persistent because it sounds so good—why wouldn't we be wired with instincts to tell us what's good for us? The problem is that we're wired for a much different environment—for a hunter/gatherer society. Our instincts aren't going to guide us unless we're on the savanna, away from fast food.
You say we're wired to crave nutrients that were "essential but rare," like fat, salt, and sugar. But those things aren't so rare anymore now that we grow and store things instead of hunting them down daily.
Our environment has gone astray. Agriculture is as old as 10,000 years, but even that is a fraction of all human evolution. It was a huge shift to growing things that simply have a lot of calories, in a few acres, that store well. That shifted us toward simple and even more refined carbohydrates.
You also say that contrary to popular belief, our societal ideal of thinness is actually consistent over time—and for a good reason: It's healthiest.
It's comforting to think that if your body isn't ideal now, it would have been in an earlier era. But that's not true. All those E-mails claiming that Miss America has gotten skinnier over the years? It's not true. It's been remarkably consistent, except for a small dip in the 1980s. What all but a handful of [too-thin] actresses and models, as well as female athletes, look like is what you'd see in the current hunter/gatherer tribe. They're all at the very slim end of the recommended BMI [body mass index] range. That is what is absolutely the healthiest, if you're achieving that by eating small servings of food and getting exercise. You should focus on healthy habits, not on the absolute weight. That means it's not healthy to achieve thinness by vomiting up meals or taking speed.
What about some studies showing that skinny folks don't live as long as those who are a bit chubbier?
When you really dig into that data, they failed to control for certain things that may specifically cause disease and make people skinny, like smoking or undiagnosed cancer. When you take that out, the healthiest body weight is right at the low end of the recommended BMI range, as long as you're achieving it in a healthy way.