Friday, January 8, 2010
The Science of Appetite
I recently came across a very interesting article, written by Jeffrey Kluger, in 2007, for Time magazine. He points out that like sex, food is required for the survival of our species. Therefore, nature makes sure that we have a hard time resisting either. Our appetite seems to have been designed to protect us from the case where we might not have enough to eat rather than an almost limitless availability of food. In the modern world, much study has been put into how our appetite works and how we can better control it. As appetite involves taste, smell, sight, texture, brain chemistry, gut chemistry, metabolism, and psychology, however, the human appetite is very complex. In many ways, though, it seems to be all about hormones. If we eat at certain times of the day, we naturally become hungry at those times and the mechanism for our hunger is ghrelin, the hunger hormone. If ghrelin were all there was to it, we and the rats would eat ourselves to death. A peptide released by the upper intestine called cholecystokinin (CCK) followed later by two hormones, GLP-1 and PYY, give us a full feeling and tell us to stop. An appetite-suppressing hormone discovered in 1994, leptin is produced by body fat itself, usually in direct proportion to how much of the tissue you're carrying. The fatter you are, the more leptin you produce. At first it was hoped that correction of leptin levels could be used to curb obesity. It turns out, however, that the leptin system in most overweight people works precisely the way it's supposed to, with hormone levels climbing more or less in lockstep with weight. The problem is, at some point the stuff simply stops working—or at least stops keeping pace with the numbers on the scale. Researchers have discovered at least two dozen other hormones and peptides that play a role in our appetite control system. From the kitchen perspective, some research involves taming appetite by trying to find a more precise way to balance the glucose loads various foods deliver to the body. Barbara Rolls, volumetrics approach targets higher volume but lower calorie foods to better control appetite. Somewhat conincidentally, I have started reading "Master Your Metabolism" by Jillian Michaels from The Biggest Loser. It is about this very topic, controlling hormones by what you put into and subject your body to. One day we may fully understand and be better able to control appetite. Based on the obesity epidemic, we are not yet there, but it is important that we get closer.