The AP reports today:
WASHINGTON - Drink a milkshake and the pleasure center in your brain gets a hit of happy — unless you're overweight. It sounds counterintuitive. But scientists who watched young women savor milkshakes inside a brain scanner concluded that when the brain doesn't sense enough gratification from food, people may overeat to compensate.The study covered in the above article:
[. . .]
A healthy diet and plenty of exercise are the main factors in whether someone is overweight. But scientists have long known that genetics also play a major role in obesity — and one big culprit is thought to be dopamine, the brain chemical that's key to sensing pleasure.
[. . .]
Yet that brain region was far less active in overweight people than in lean people, and in those who carry that A1 gene variant, the researchers reported. Moreover, women with that gene version were more likely to gain weight over the coming year.
It's a small study with few gene carriers, and thus must be verified, Volkow stressed.
Still, it could have important implications. Volkow, who heads NIH's National Institute of Drug Abuse, notes that "dopamine is not just about pleasure." It also plays a role in conditioning — dopamine levels affect drug addiction — and the ability to control impulses.
She wonders if instead of overeating to compensate for the lack of pleasure — Stice's conclusion — the study really might show that these people with malfunctioning dopamine in fact eat because they're impulsive.
Relation Between Obesity and Blunted Striatal Response to Food Is Moderated by TaqIA A1 AllelePodcast interview with Eric Stice.
E. Stice, S. Spoor, C. Bohon, and D. M. Small (17 October 2008)
Science 322 (5900), 449. [DOI: 10.1126/science.1161550]
Individuals whose reward centers of the brain respond sluggishly after eating prefer calorie-dense foods, which may account for their greater propensity to gain weight.