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 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 small but first-of-a-kind study even could predict who would pile on pounds during the next year: Those who harbored a gene that made their brain's yum factor even more sluggish.
“The more blunted your response to the milkshake taste, the more likely you are to gain weight,” said Dr. Eric Stice, of the Oregon Research Institute who led the work, published in today's edition of Science.
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 key to sensing pleasure.
Eating can temporarily boost dopamine levels. Previous brain scans have suggested that the obese have fewer dopamine receptors in their brains than lean people. And a particular gene version, called Taq1A1, is linked to fewer dopamine receptors.
“This paper takes it one step farther,” said Dr. Nora Volkow of the National Institutes of Health, a dopamine specialist who has long studied the obesity link. “It takes the gene associated with greater vulnerability for obesity and asks the question why.”
It's a small study with few gene carriers, and thus must be verified, Volkow stressed.
Still, it could have important implications. Volkow 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.