are “paleo” dieters engaged in fantasy?

Via Jamelle Bouie — Laura Miller in Salon reviews a new book, Paleofantasy, in which evolutionary biologist Marlene Zuk attacks the “paleo” diet trend. She questions whether our ancestors really ate the way we think they did and, more importantly, whether it necessarily follows that our diet must mimic theirs.

Zuk’s answers are that our ancestors probably ate whatever they could get their hands on, and that whatever they ate, surely our bodies are adapted to the modern diet by now, because evolution can happen really quickly.

As to the first point, that’s undoubtedly true. Humans are almost certainly at least part-time omnivores, as are many other animals, from the obvious (rats, wolves/dogs) to the somewhat less expected (deer). But there are two reasons this observation, on its own, is less than helpful. First, of course, the mere fact that an organism is adapted to eat “whatever it can get its hands on” doesn’t mean that some foods aren’t significantly healthier for the organism than others. Second, and more importantly, it’s inarguable that refined sugar and highly refined starch were simply unavailable in significant quantities in the ancestral environment. There was no white bread and there were no Snickers. That in and of itself, of course, doesn’t mean that such foods are dangerous; nobody had coffee in the ancestral environment, either, but most people who self-identify as “paleo” probably don’t object to a nice cup in the morning. Still, as a starting point, it may be helpful to at least point out some things our ancestors definitely were not eating — or at least had very limited access to.

As for her second point, it’s certainly true that evolution can happen very quickly. Zuk gives the example of lactase persistence. Humans before several thousand years ago did not produce lactase after childhood; now a substantial minority of us do. That transition happened very quickly, and it’s a useful adaptation indeed. But pointing this out, without more, may paint a misleading picture of how evolution happens. The availability of a new food source does not mean that humans will auto-magically adapt themselves to be able to eat such a food source with no adverse health consequences. Substantial evolutionary change would likely require:

  • A new food source.
  • A gene mutation or series of mutations that enables the organism to take advantage of the food source.
  • Environmental pressures that make using the new food source critical to the organism’s survival.
  • And the difference in survival rates occurs during or before the organism’s reproductive period. (I.e., not just in old age.)

If any one of those links is missing, then natural selection is far less likely. And even if all of those conditions are satisfied, and the organism adapts well enough to this new food to use it to gain a survival advantage, that doesn’t mean that the new food source is the healthiest option for the organism. The food source may well produce negative health consequences which are sub-evolutionary in scale. Lactase persistence itself may well be such a case — it’s entirely possible that eating dairy gave our ancestors a tremendous survival advantage in harsh ancestral environments, while also being suboptimal for ideal health outcomes. The two things, in other words, do not contradict each other. Indeed, even leaving aside genetic changes, it seems indisputable that the development of grain-based agriculture enabled rapid human population growth, and hence was a positive cultural adaption enabling greater opportunities for our offspring to succeed. That is a separate question from whether a grain-based diet is good for the human body.

Finally, I should say that I take Zuk’s point. Some of the hype around “paleo” diets is clearly based on nostalgia for a rosy-tinted ancestral past. But much of what gets lumped under “paleo” is perhaps better described as “low-carb,” “low-sugar,” or “low-refined-carb.” And the rationale for such diets does not actually depend on an evolutionary explanation at all. Robert Lustig and Gary Taubes are making their pitch based on arguments about the biochemistry of carbohydrate metabolism in contemporary humans, not some idealized reminiscence of a cave-dwelling Eden. Their argument may be wrong — and many, many people have said that it is — but it is not wrong because of a lack of understanding of evolution.

(And finally-finally, I’ll just note that reducing refined carbs in my own diet has been closely associated with a dramatic reduction in both weight and blood pressure. I’m not 100% convinced of the Lustig-Taubes theory myself — there are certainly other possibilities for the correlation, such as a placebo effect or the idea that it’s just harder to eat as many bacon calories as pasta calories. But whatever the reason, it’s been working quite well for me for the better part of two years, and I think I’ll probably keep it up.)

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