Cooking clue to human dietary diversity.

F or primates, humans have pretty peculiar diets. Most often, our food intake includes large amounts of starchy plant food, together, particularly in developed countries, with considerable quantities of vertebrate muscle and other soft tissues. No other large primate eats like this. Instead, our near relatives tend to obtain most of their calories from the simple sugars in fruits and most of their protein from a single profligate photosynthetic enzyme in leaves. We are really very odd. Even the use of human “diets” in the plural indicates this. Compared with the comparatively stereotyped food intake of wild primates, the variety of diets consumed by our single species is staggering. Even if geographical factors are excluded, the diversity persists. Very few of the alternative dietary regimens recommended by experts (and others) have been totally refuted as biologically unfit, even when dietary dogmata are contradictory. Although many guidelines focus on the merits of protein vs. carbohydrate vs. lipid, or on plants vs. animals, some are directed instead at the raw vs. cooked dichotomy. All this conveys something quite clearly: our bodies do not provide us with adequate sensory or hormonal feedback to “tell” us what they want, and that we, as organisms, do not have enough “inside” knowledge as to what we are optimally built to consume. Otherwise, surely there would be no argument. So what threw all these confusing choices at us? One of the most important recent ideas is that cooking has opened up a whole range of items to us that either could not be digested, or else could not be consumed in a reasonable time period, unless heat was available to modify them (1). Commercial starches are all modified before sale, but the effect of heat on the digestion of muscle (i.e., meat) is less well known. However, in PNAS (2), Carmody et al. at Harvard University cap a series of articles on the benefits of cooking by offering definitive evidence in mice that the cooking of both meat and starchy tubers enhances their digestion significantly. The evidence comes from balanced short-term experiments on the ingestion of raw vs. cooked starchy tubers and meat that considered “pounding” (mechanical fracture and fragmentation using a mallet followed by pestle and mortar) as a separate factor. The evidence points strongly to the dominance of heat treatment as a digestive aid. Mice fed on raw diets lost some of their body weight, whereas those on cooked diets generally maintained it. Curiously, even naive mice preferred roasted meat, whereas experience was apparently needed to prefer roasted tubers. The importance of these experiments lies in how far the results can be applied to humans.