paleo logic

Today I ran across the “paleo diet.” Essentially, it’s the idea that the human body is better conditioned to eat a diet resembling the one our paleolithic ancestors subsisted on than a “modern” diet. Eat lots of meat, fish, eggs, lots of fat, some fruit root vegetables, nuts… eliminate all sugars, wheat, refined oils, salt, legumes, grains… dairy seems to be optional. Why is dairy optional? Because. That’s why.

The theory is that,

…in the 10,000 years since the invention of agriculture and its consequent major change in the human diet, natural selection has had too little time to make the optimal genetic adaptations to the new diet. Physiological and metabolic maladaptations result from the suboptimal genetic adaptations to the contemporary human diet, which in turn contribute to many of the so-called diseases of civilization.

Those “diseases of civilization” are things like heart disease, diabetes, asthma, Alzheimer’s, acne, obesity, and of course, cancer.

As a lifestyle kind of thing, “let’s have some bacon” I’ve got no beef (or maybe I have no legume) with this diet. But I do have a problem with sciencyish hokum masquerading as fact.

First of all, it’s a mistake to equate genotype with phenotype or morphology. We may share a genotype (basic genetic similarities) with paleolithic man, but we certainly don’t share a phenotype (characteristics, traits, appearance) or even morphology (systemic operation and configuration) with those ancient forebears. We’re taller, for one. We have better tools. We’re more attractive. We’re smarter. We live longer.

Each of those differences has profound implications for nutritional science. We’re bigger, which means that we not only require more calories than our smaller ancestors, but it also means that our general nutritional requirements are going to be different. We have better tools. That means that, on average, our caloric expenditure has gone down. We spend more of our time idle. That means that we’re more likely to store excess calories as fat. We’re more attractive. Not just my opinion, there’s a good deal of evidence to suggest that women (but not men) have consistently, generation after generation gotten better and better looking and I think there’s a strong case that improving beauty is a strong indicator of improving nutrition. We’re smarter. Not just better educated or more advanced, but actually smarter. There’s a wealth of information that indicates that g–the measure of general intelligence–has increased across cultures over time. Again, a steadily increasing intelligence would presume a steadily improving nutritional base. We live longer. This is the real proof in the sugary, sweet, agriculturally-dependent pudding: we live a lot longer. Decades and decades longer. And… maybe, just maybe, the incidence of diseases like asthma, heart disease, Alzheimer’s, obesity, and cancer correlates better with age than with diet. I know, radical assumption, that. As for acne… frankly I don’t buy it. I’ll bet showers, soap, and the invention of basic hygiene have reduced acne.

But wait, it gets better.

The idea that we evolved 200,000 years ago to eat a certain diet and just haven’t had the time to adapt in the last 10,000 years is… well, it’s dumb. First of all, it’s very likely that humans have been farming grains and legumes for as long as 100,000 or even 200,000 years. Secondly, even if we allow for only 10,000 years since the spread of agriculture, that gives of 400-500 generations in which to adapt to the new diet. Evolutionary adaptation is not simply time-dependent. It’s dependent on selective pressure and time. If the selective pressure is great enough, random mutation can induce widespread evolutionary change in very few generations. And if we assume the argument that our bodies were ill-equipped to handle the dietary shift that the advent of agriculture brought about, then we must acknowledge that such a radical shift would have generated tremendous selective pressure. Or in other words, for agriculture not to result in widespread famine and death, it would either have to have not been a horrible break from ancestral diets or, if it were, then we must have adapted to those changes.

And what of that paleolithic diet anyway? How much meat did they actually eat? What’s the “optimal” proportion of meat to tuber? Who knows? No one; Tuesday night dinners weren’t fossilized until Swanson came along.

Now it’s true that we’re fatter and older than our paleolithic friends, but only one of those things is actually bad. The few studies that were done on the sparse paleolithic populations that were still extant in the last century did provide some evidence that their populations were resistant to some diseases like obesity, asthma, and heart disease. These studies also indicated that these populations were ill suited to “modern” diets. But these studies are hardly conclusive. First,  obesity isn’t caused by eating evil legumes, it’s caused by consuming too many calories and burning too few. There’s a lot of actual science behind calorie reduction as a means to extend longevity and improve overall health. The paleolithic diets in these cases were also low calorie diets. With no control established, it’s simply disingenuous to claim that the paleo diet, rather than calorie reduction correlated with overall health. Note: it’s wrong to even imply correlation much less causation.  As for sensitivity to “modern” diets, that’s evidence that cuts both ways. These cultures were reproductively isolated from the rest of humanity and as a result may not have adapted as the rest of us did. Furthermore, because these populations were reproductively isolated for so long, they’re also genetically unique populations. In other words, it’s not only impossible to control for calories in these studies, it’s also impossible to control for genetic differences. At best, the most we can really say is that a tiny population of people in New Guinea seemed to do OK without much bread.

OK.

None of this is to say that you shouldn’t necessarily try this diet. If it sounds yummy to you–lots of fresh fish, lots of bacon, tasty fruits and nuts, whole milk and farm fresh eggs (yeah, livestock domestication came with agriculture, but who’s counting), and yummy yogurt (because… well, this one’s got me stumped. Yogurt would have to be post agriculture and since yogurt contains live bacteria, I would think that of anything, we’d be least adapted to its consumption)– then go for it.

But just don’t do it because you think that your body might not be “adapted” to corn, tomatoes, apples, rice, beer, wine, or clean drinking water.

And certainly don’t adopt this diet if you suffer from health complications that would make the diet a definitively bad choice for you.

Otherwise, go for it. But spare me the pseudo-science.

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