Of course, there are those lucky few—people who don’t soothe themselves with food or find it hard to resist foods’ siren songs unless their stomach is empty. “You can put five people in a room with a cake,” says eating-disorders researcher Gayle Timmerman, Ph.D., R.N., of the University of Texas at Austin; “there will be one or two people who couldn’t care less about the cake, unless they’re really hungry. But at least a few of them will have a hard time thinking about anything but the cake.”
Genetic programming may determine why at least some of us are the cake-obsessing types. Last year, Hudson and his colleagues reported that binge eating (along with a tendency toward obesity) often runs in families. “If you have a relative who’s a binge eater, you’re twice as likely to have problems with binging yourself,” he says. “And you’re also about two and a half times as likely to become obese.”
Research by Volkow and Gene-Jack Wang, M.D., at Brookhaven National Laboratory in Upton, New York, suggests a neurochemical basis for why some people might be more likely to become “addicted” to food than others. Using positron emission tomography (PET) scans—computerized images that show activity levels in various parts of the brain—Volkow and Wang looked at the brains of the most likely candidates for the “food addict” label: a group of 10 extremely obese women and men. They found the group had fewer receptors for dopamine in their brains than did a similar group of normal-weight controls—suggesting, perhaps, that an impaired dopamine system might make obese people more sensitive to the rewarding properties of food.
Last October, researchers at the University at Buffalo, State University of New York, uncovered a possible genetic link to dopamine’s influence on overeating. When they looked at the DNA of 29 obese people and that of 45 slightly overweight or normal-weight people, the researchers found that about half of them had a form of a gene linked to having fewer dopamine receptors in the brain. The scientists then gave the study subjects computer tasks to perform with their favorite foods (like chocolate and potato chips) as a reward—more work, more food. They found that the obese people with the fewer-dopamine-receptors gene worked twice as hard for their food rewards than the other obese group who didn’t have the variation—and much harder than those in the normal-weight groups of either genetic background. The investigators speculated that without as many dopamine receptors, the obese group might have had to seek out excess reward from their food. (What about those people who had the gene, but remained a normal weight? The researchers speculated that they might have found other, nonfood ways to satisfy their need for rewarding experiences—for example, smoking or exercising.)
Do obese people eat more, perhaps, to stimulate the dopamine pleasure circuits in their brains, as addicts might do by taking drugs? “I think so, but that’s just one piece of what’s involved,” says Wang. “Humans are complicated, and many factors affect the dopamine system, including social behavior and sleep patterns.” But the model provides tantalizing clues as to why so many disordered eaters eventually become overweight.