What’s cooking?

Monday, February 23rd, 2009

What’s cooking? The driver of evolution, says Richard Wrangham, of Harvard:

Cooking alters food in three important ways. It breaks starch molecules into more digestible fragments. It “denatures” protein molecules, so that their amino-acid chains unfold and digestive enzymes can attack them more easily. And heat physically softens food. That makes it easier to digest, so even though the stuff is no more calorific, the body uses fewer calories dealing with it.

In support of his thesis, Dr Wrangham, who is an anthropologist, has ransacked other fields and come up with an impressive array of material. Cooking increases the share of food digested in the stomach and small intestine, where it can be absorbed, from 50% to 95% according to work done on people fitted for medical reasons with collection bags at the ends of their small intestines. Previous studies had suggested raw food was digested equally well as cooked food because they looked at faeces as being the end product. These, however, have been exposed to the digestive mercies of bacteria in the large intestine, and any residual goodies have been removed from them that way.

Another telling experiment, conducted on rats, did not rely on cooking. Rather the experimenters ground up food pellets and then recompacted them to make them softer. Rats fed on the softer pellets weighed 30% more after 26 weeks than those fed the same weight of standard pellets. The difference was because of the lower cost of digestion. Indeed, Dr Wrangham suspects the main cause of the modern epidemic of obesity is not overeating (which the evidence suggests — in America, at least — is a myth) but the rise of processed foods. These are softer, because that is what people prefer. Indeed, the nerves from the taste buds meet in a part of the brain called the amygdala with nerves that convey information on the softness of food. It is only after these two qualities have been compared that the brain assesses how pleasant a mouthful actually is.

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