By Diana Hsieh
The following comments on the validity of a evolutionary approach to nutrition are from an email that I wrote to an Objectivist philosopher skeptical of the paleo diet. (The email was sent many moons ago, and I only just found it again.) My comments stand pretty well on their own, I think, and I hope that they'll be of interest to folks interested in thinking about paleo in a philosophical way.
I cannot point you to a single study that definitively proves the superiority of a paleo diet. For a hundred different reasons -- most of which probably aren't on your radar -- such a study is not possible. (Gary Taubes and Mike Eades have written on that problem.) Nonetheless, a whole lot of smaller, more delimited studies (as well as well-established biology) support the claims made by advocates of a paleo diet. Plus, people report looking, feeling, and performing better -- with improved lab values -- on a paleo-type diet. Each of us has our own experiences and experiments to draw on too.
Hence, as I said in a thread on Facebook: "I think I've got very good grounds for saying that a paleo diet is (1) healthy for most people, (2) far superior to the diet of most Americans, (3) exceedingly delicious and satisfying, and (4) worth trying to see if you do better on it, particularly if you have certain kinds of health problems."
I'm not claiming certainty, nor do I assume that my current diet is optimal. We have tons to learn about nutrition and health. Yet that's hardly a reason to ignore what we do know -- or to suppose that we can just keep eating however we please without experiencing pernicious consequences down the road.
Moreover, people are doing themselves harm by eating the standard American diet. In my own case, I was on my way to type 2 diabetes (based on my doctor's blood glucose tests) and liver disease (based on a CT scan showing non-alcoholic fatty liver disease). We can't assume that the standard American diet is a safe default just because it's all around us -- just as people shouldn't assume that the standard American religion is a safe philosophical default.
To address your skepticism about an evolutionary approach to nutrition, let me ask you the following... Imagine that you were given a dog to care for, but you'd never seen or heard of a dog before. Would you say that the fact that dogs are very close relatives of wolves is irrelevant to the question of what you ought to feed this dog? Wouldn't that evolutionary fact suggest that the dog needs meat, meat, and more meat -- not tofu or corn or alfalfa?
That evolutionary inference certainly wouldn't be the last word on proper diet for the dog by any stretch of the imagination. Yet that inference would help guide your inquiry into the optimal diet for the dog -- and guide your feeding of him in the meantime. That evolutionary perspective would be particularly helpful if the government and its lackeys were busy promoting a slew of false views about optimal canine diet. Ultimately, it would help integrate and explain your various findings about canine nutrition, since the nature of the canine was shaped by its evolutionary history.
On this point, your comparison to evolutionary psychology is not apt. Evolutionary psychology is a cesspool. But that's not because inferences from our evolutionary history are difficult, although that's true. Evolutionary psychology is a cesspool because it depends heavily on some false philosophical assumptions -- particularly determinism and innate ideas.
The same charges cannot be made against an evolutionary approach to nutrition. We know that every organism is adapted to eat certain kinds of foods rather than others. We know that human biology was shaped over the course of millions of years, during which time we ate certain kinds of foods but not others. That suggests the kinds of foods that we're best adapted to eat. Moreover, we can see in skeletal remains that when people switched to other kinds of foods, particularly grains, they declined remarkably in basic measures of health. Then consider what know about the nature of wheat, including its effects on the gut. Top that off with the positive effects people experience -- improved well-being, fat loss, better lab values, less autoimmunity -- when they stop eating wheat. Then you've got a compelling case against eating wheat.
The evolutionary perspective is not merely a useful starting point in such inquiries, to be discarded with advancements in modern science. It's relevant causal history: it explains why we respond as we do to wheat. That enables us to integrate disparate findings about wheat (and other foods) into a unified theory of nutrition. That's hugely important to developing nutrition as a science.