It was a difficult question for obesity researchers: do some people overeat because they find eating more pleasurable or gratifying than others? Logically, that makes a lot of sense--it's a time-tested principle of psychology: if a behavior feels good, we'll keep doing it. But a new study published today in the journal Science adds to a growing body of research suggesting the opposite: that women who derive less pleasure from eating may eat more to compensate, putting them at higher risk for weight gain and obesity. The research also discovered a particular genetic trait that, when present, is associated with an even stronger relationship between low sense of reward and overeating.
"If you ask overweight individuals if they crave food, I really think they are legitimately thinking it's more rewarding," says study author Eric Stice, a senior scientist at the Oregon Research Institute. "They'll say they're really sensitive to the rewards. But when you look at the brain scans you get a different picture."
Previous brain imaging studies have looked at what happens when we look at pictures of food. In those cases, obese individuals tend to anticipate a higher level of satisfaction of eating the pictured food than lean individuals do, supporting the idea that the people who overeat are the ones who find it more rewarding. But the Science study was the first to do those same fMRI scans while participants were actually eating--or, in this case, drinking a chocolate milkshake. "Nobody had ever administered food to people in a brain scanner and looked at what happens in the brain while you're eating," says Stice. "Now we have evidence that, when you give an obese individual a chocolate milkshake, there's less of a response going on."