From The New York Times:
“Bet you can’t eat just one” (as the old potato-chip commercials had it) is, of course, a bet most of us end up losing. But why? Is it simple lack of willpower that makes fatty snacks irresistible, or are deeper biological forces at work? Some intriguing new research suggests the latter. Scientists in California and Italy reported last week that in rats given fatty foods, the body immediately began to release natural marijuanalike chemicals in the gut that kept them craving more.
The findings are among several recent studies that add new complexity to the obesity debate, suggesting that certain foods set off powerful chemical reactions in the body and the brain. Yes, it’s still true that people gain weight because they eat more calories than they burn. But those compulsions may stem from biological systems over which the individual has no control. “I do think some people come into the world, and they are more responsive to food,” said Susan Carnell, a research associate at the Columbia University Institute of Human Nutrition. “I think there are many different routes to obesity.” In the recent rat studies, by a team from the University of California, Irvine, and the Italian Institute of Technology in Genoa, the goal was to measure how taste alone affects the body’s response to food. Among rats given liquid diets high in fat, sugar or protein, the ones who got the fatty liquid had a striking reaction: As soon as it hit their taste buds, their digestive systems began producing endocannabinoids, chemicals similar to those produced by marijuana use.