Hamblin: The thing I concede to people with things like fad diets is, like a diet where you don't eat yellow things, okay, well you're getting some placebo effect. You're developing a sense of identity and awareness about what you put in your body. So what about the benefits of belief?

Levinovitz: The question I ask, then, is do we have empiric evidence that irrational beliefs about the power of food lead to better real-world outcomes? In other words, I might be convinced that it's worth thinking that gluten causes autism or that Paleolithic dieting is good for you if having those beliefs were genuinely better in terms of outcomes. To take a similar argument with religion: Emile Durkheim, sociologist of religion—he didn't think religion was true. But he thought it was necessary for cultivating ethics. Religion was a sort of belief engine that would keep people good. The argument then is, if we don't have this set of beliefs, how are we going to get along? Why would we treat each other nicely? We'll just dissolve into chaos. Which is not true. We can treat each other just fine without a false belief system that tells us to. I would argue the same thing for living healthfully. There's just no reason to think that quasi-religious beliefs about the miraculous powers of foods, or the demonizing of foods, benefit our health. And if that's the case, then we should work to get rid of them.

And I think it does hurt our health, because we decide on easier things like miracle berries. And we live in fear, because the world is filled with these invisible antagonists of modernity: toxins and chemicals and radio waves. If there's one thing we do know it's that being terrified of life is not good for you.

Hamblin: At least we're not going to war over diets.

Levinovitz: Well, if you look back in history, the first thing leaders do to introduce an us-them dichotomy is introduce dietary rules. It's the best thing: What do we eat? What do they eat?

As for what we eat, I think the USDA and academic nutritionists need to stop coming out with nutritional guidelines. Because it's an extremely fallible science that's constantly contradicting itself, and it makes people think that science is not to be trusted. First they thought this about cholesterol, now they think that? I guess we just can't trust those pointy-head scientists! You can tell people to eat in moderation and get physical activity, and then you don't have to flip-flop on anything. And 99 percent of doctors will agree that the problem is not that people eat in moderation but slightly too much dairy or something.

Hamblin: My sense is that the nutrition guidelines now are more reactive than anything. There are so many people out there who believe that carbs are just bad, for example, that it makes sense to have a confluence of experts going on the record saying that moderate whole-grain intake is part of a healthy approach to life.