Almost directly copied and pasted from an email, as followup to a discussion re: insulin levels, diabetic risk, and obesity. Mostly the thing about slavery I think is probably dead accurate, and it's a theory I've never heard before. He came up with it all on his own, 'cause he's wicked smaht.
"There’s plenty of evidence that high levels of circulating insulin trigger a shift in metabolic pathways. Fatty molecules are preferentially moved from blood-borne lipoproteins to adipocytes, leaving other tissues in a state of fat deprivation. The brain reads this as a state of relative starvation, so it slows metabolism and activates hunger and craving. This triggers the intake of more food, and coupled with the increase in adipocytes, this cranks insulin levels up again. The cycle spirals upwards, and the end result is obesity, constant craving, tissue insulin resistance and high levels of circulating insulin.
"There are a bunch of experiments in which lowering circulating insulin makes lab mice pretty much impervious to diet-induced obesity. There are also human experiments in which low carb, low glycemic index diets reduce weight more effectively and result in higher metabolic rates (measured by calories burned) than a low fat diet with the exact same protein and calorie intake. Low carb diets also seem to improve post-prandial energy availability (no “post-lunch dip”), which encourages activity, further lowering insulin resistance and burning more calories.
"From a teleological point of view, this all makes perfect sense. Our endocrine/nutrition systems evolved long before our ancestors learned to cook or grind grains to produce high glycemic index foods. For millions of years, the only high glycemic index foods available to mammals in large quantities were ripened fruits, which appeared for a limited time in great abundance--but mostly in autumn, just before the long deprivation of winter. To take advantage of this bounty, it makes sense that we would have evolved a metabolic switch, turned on by large spikes in circulating insulin. We evolved to take advantage of the harvest season by flipping into storage mode and building up our fat stores for the lean times ahead.
"I also think the high rate of obesity, diabetes [and salt-responsive hypertension] in African Americans (which includes all income levels) may be a direct result of unnatural selection pressures of slavery. On slave ships in particular, fat storage and reduced metabolic rates (not to mention sodium retention) came with a distinct survival advantage. The slaves with the highest circulating insulin levels survived the voyage."
So, yuh. I've absolutely heard it posited that metabolic systems best attuned to survive relative scarcity will then be more prone to obesity etc. when faced with caloric over-availability, but the idea that specifically the single event of the metabolically extremely traumatic trans-Pacific voyage would be enough to act as a defining Darwinian moment in the genetic makeup of an entire ethnic group is intriguing, and absolutely makes sense. What I can't find are any studies comparing propensity for diabetes/salt-responsive hypertension in Africans and African-Americans with similar starting weights, diets, and exercise habits.
