Richard Wrangham a professor of biological anthropology at Harvard and the author of “Catching
Fire: How Cooking Made Us Human” was interviewed on NPR. He worked with Jane Goodall, and is director of the Kibale Chimpanzee Project in Uganda. According to Wrangham, great apes prefer cooked food to raw food or they have no preference. They prefer cooked meat to the raw meat that they occasionally form hunting parties to obtain, but are hampered by not controlling fire. Great apes, when given a choice, never prefer raw food to cooked food. Chimps will go into areas of wildfires and eat foods that they would never eat raw. Meat (at least wild meat) is tough when raw, but is much more easily assimilated when cooked.
Cooked food increases the proportion of nutrients that you actually digest. This was not widely appreciated for many years because scientists sampled the food going into the mouth then compared it to fecal output. But fecal digestibility does not really look at assimilation. We can only assimilate proteins in the small intestine, not the large intestine.
Bacteria in the large intestine may use parts of foods that their human host has no access to. It is better to look at food at the end of the small intestine, but that tends to be difficult. But it is possible to do this non-invasively by extracting food from people who have ileostomy bags that are located at the end of the small intestine and who thus do not send food through the colon. The digestate is analyzed for specific kinds of food nutrients. This kind of research shows that there is a difference in the way that cooked or raw food is digested.
For instance, more nutrients are obtained from cooked carrots than raw carrots, although fiber is lower. When you look at ilium output, all the proteins in cooked eggs are digested, but only 55-65% of raw egg proteins (mostly from the whites) are digested.
Rats were given rat chow pellets and air puffed rat chow pellets (think puffed rice vs. rice). The same number of calories were given, the same energy expenditure was used to eat the food, but those rats with the softer puffed pellets grew larger and had 30% more body fat. After a meal the rats that had the softer food had a lower body temperature- lower metabolic rate. When we turn beef into ground beef or grains into flour we have a greater net caloric gain.
In Chinese medicine, raw food is considered undesirable, seen as too taxing to the Spleen. Soups, cooked food, are considered the most desirable because the most nutrients can be assimilated. Further in agriculture where human waste was used as fertilizer, cooking significantly reduces diarrhea and other diseases. But raw food can help us by increasing fiber, an increasingly difficult to find in a society of processed food. Raw food by reducing nutrient intake, can give us a reduction in weight. It results in less rheumatoid arthritis. Vitality is increased. Unlike classical China, our society has too much food, and ultimate assimilation is undesirable until we revamp our food distribution. As practitioners we need to carefully consider the Chinese medicine prohibitions on raw food.