Saturday, July 24, 2010

Tubers and Evolution

Stephen Guyenet, whose blog Whole Health Source you'll note is in my blog roll, has been very active in discussions about ancestral diets.  His blog introduced my to the whole topic, or, I should say, inspired me to pay attention to it.

One of his favorite topics is carbohydrates and their role in the diet.  He's of the opinion that many grains, unless properly prepared, are quite harmful  to humans, as are, to a lesser extent, tubers (potatoes and yams and the like).

But he parts from many other advocates of ancestral diets on low-carbohydrate diets.  He notes they work for many people, but also observes that healthy groups eat lots of carbs, and don't suffer the ill effects that most do.

...The Kitavans, for example, don't seem to have heart attacks or strokes (although no autopsies have been done so we don't know how much atherosclerosis they have).

They get 69% of their calories from high-glycemic starchy tubers, and their 21% fat comes mostly from coconut so it's highly saturated....
(The Diet-Heart Hypothesis: Oxidized LDL, Part II)
The paleo diet (small caps, to differentiate it from the book of the same name), suggests that many of the foods we eat are problematic for us because we are only recently evolved to eat them.  Milk is the most commonly cited example, but there are others.
From what I've read of Stephan's writings, he agrees with a good bit of the premise of the paleo diet, but...
We part ways on the issue of carbohydrate. [Mark Sisson] suggests that eating more than 150 grams of carbohydrate per day leads to fat gain and disease, whereas I feel that position is untenable in light of what we know of non-industrial cultures (including some relatively high-carbohydrate hunter-gatherers). Although carbohydrate restriction (or at least wheat and sugar restriction) does have its place in treating obesity and metabolic dysfunction in modern populations, ultimately I don't think it's necessary for the prevention of those same problems, and it can even be counterproductive in some cases. Mark does acknowledge that refined carbohydrates are the main culprits.
(Book Review: The Primal Blueprint)
I don't know enough about the topic to have an opinion one way or another.  Since I've found that I do better on a low-carb diet, and carbs tend to make me feel poorly (which may simply be a sign of a metabolism damaged by other factors), I avoid them, but I've filed this little unresolved dispute away in the back of my brain.

Gary K in BFT's list brought my attention to this NY Times article.  It's about developments in our understanding of recent human evolution.  They apparently have a way, not well described in the article, of determining which bits of the human genome are of recent vintage.  I found this part quite interesting, in light of the above:

She found particularly strong signals of selection in populations that live in polar regions, in people who live by foraging, and in people whose diets are rich in roots and tubers. In Eskimo populations, there are signals of selection in genes that help people adapt to cold. Among primitive farming tribes, big eaters of tubers, which contain little folic acid, selection has shaped the genes involved in synthesizing folic acid in the body, Dr. Di Rienzo and colleagues reported in May in the Proceedings of the National Academy of Sciences.
This suggests, but does not prove, that people who eat tubers may be evolving into that role, just as those who eat cow's milk are evolving into that role.  And, just as many people without the proper genome don't do well eating cow's milk, so they may have problems with high-carbohydrate diets.  Or it may be the other factors that are causing the problem. 

What I do find interesting is that Di Rienzo does not mention genetic activity in those eating grains, or agricultural diets.  Does that indicate that the adaptations to eating milk and tubers are older, and have had more time to work on the genome?

Unfortunately we still don't know, but it's an interesting data point to file away.  But it does suggest that if you don't do well on a high-carb diet, you'd be well advised to listen to your body and eat in a manner that keeps it healthy.