This continues a series of basic posts each focusing on a single key topic that, in modern society on an average diet, has gone badly awry with negative consequences. As I am not by any stretch of the imagination the first to discuss these topics, the majority of these posts will simply be referring you to excellent background resources.
Both fats and carbohydrates can be used by the body as sources of energy for movement, thought and the basic processes that keep us alive and procreating (protein, while able to be used for energy when necessary, plays a largely structural role under ideal nutritional conditions). The real question, then, is how much of each to consume. Assuming that your goal is to maximize both health and longevity, I and many others would argue that we are designed to function best on a diet high in fat. Carbohydrates were most often available to our pre-historical ancestors in the form of seasonal grains and seeds. These were hardy, could be gathered and stored, and kept us alive through winters’ shortage of tasty, fat-laden critters. This reliance on high-carbohydrate foods, however, was (and in many impoverished areas around the world still is) about survival.
In moving to agriculture, we accepted subsistence on carbohydrate-laden foods and in return we no longer were required to travel nomadically, following herds of whatever we thought most likely to ensure our survival. Keep in mind that this move to subsistence farming may have been driven more by our eating all the megafauna rather than by some particular innate desire to be farmers. This was then a Faustian bargain: continued human survival in exchange for reduced lifespans. Note that this reduction wasn’t universal and populations with a long-term reliance on grain-based diets certainly developed protective mutations. Just because your genetic stock may have a few compensatory mechanisms, however, doesn’t particularly mean subsisting primarily on carbohydrates is good for you. And most modern carbohydrates (pasta, white bread, pizza crust, sugary cereals, etc.) hardly resemble what our ancestors may have chosen to eat when all else failed.
Personally, given the evidence to date, I try to keep my carbohydrate intake below 100g/day and, when I do eat carbohydrates, I seek to minimize the glycemic index (and enjoy informative musings on the same) of anything I eat (particularly by avoiding sugars and heavily refined flour-based items).
Five chunks of related blogosphere wisdom: