December 16, 2013

Big, beautiful, bouncing... Brains.

Bounce monkey brain, bounce!
As I mentioned last time, I've become intrigued by the relationship between brain function and diet: does the brain run best on a particular set of fuels?  Does peak mental performance require some specific type of foods?  Or, can we stuff our faces with garbage and expect to have tip-top noggins?

I've started my research by examining the evolutionary context for our big brains.  Specifically, what type of dietary environment supported the evolution of our minds?  Can we learn anything from examining the paleontological record of our ancestors?

I've learned a few interesting things so far, all related to the coincident timing of certain events during the rapid encephalization, or brain growth, that culminated with the human brain.  The first that jumps out is the earliest evidence of stone tools, which roughly coincides with the appearance of the species Homo habilis around 2.3 million years ago (mya).  At the point that tool use became evident, the brains of H. habilis were roughly "the same size as that of a chimpanzee."

It was over the next ~1 million years that brain growth was most dramatic, where the 600 cc Homo brain case nearly doubled in size to ~1,100 cc in H. erectus.  Although the exact timing is still controversial, H. erectus was the first species to demonstrate the controlled use of fire, with evidence taking the form of obvious ovens by around 200 thousand years ago (kya) although some argue that cooking existed as a technology for much longer.  If we assume cooking really took off at the more recent end of the possible range, this very closely aligns with the emergence of anatomically modern humans - the oldest fossilized remains that closely resemble modern humans - and represents the other, major coincident event that seems to correspond with a major advance in the human lineage.

These examples of critical cultural advances - tool use and control of fire - both indicate that our ancestors relied heavily on hunted or scavenged animals as a source of nutrient-dense food as animal bones marred by both tool marks and burn marks have been observed.  These facts, combined with analyses of both current and inferred hunter-gatherer diets, suggest that the eating of animals was an important factor in the development of the human brain (sorry, vegetarians).

That being said, the evidence also seems to suggest an important role for the consumption of significant plant-based food in our ancestors' diets as well: fruit, tubers, nuts, and vegetation.  Supporting an energy-hungry organ like the human brain takes a lot of raw material and energy, so it's reasonable to assume that our ancestor's ate anything they could hunt... or gather.  However, the caveat to applying this "eat what you can" or omnivore approach to our modern diets is the relatively recent emergence of agriculture on the scene ~10 kya.  The explosive growth in the availability of carbohydrates allowed by agriculture is the cause, hypothesized by Gary Taubes and others, of many of the modern maladies of civilization, including obesity, diabetes, heart disease, and cancer.  For the most part, I buy the argument that too many carbohydrates is likely driving the rapid rise in obesity and related comorbidities, but that is for another day.

Regarding brain function, the open question for me is this: if our brains are hungry organs and we evolved to eat anything we can, shouldn't more of everything (including carbohydrates) be better for peak brain function?  Isn't it possible that the best diet for brain function may not be the best diet for long term health?  I don't feel confident with the range of possible answers to this question, but my rough analysis of our brain evolution would seem to suggest that an emphasis on animal protein and the "gatherable" fruits, nuts, and vegetables may represent a sweet spot for brain function as well as overall health.  In future posts I hope to explore the mechanisms of brain metabolism in the context of different levels of nutrients with the hope to learn more about how the brain prefers to get it's fuel.  Perhaps the hunter-gather diet is best of brains, but I will wait for more evidence before I make the call.

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