Brain’s reaction to yummy food may tip the scales

By LAURAN NEERGAARD
The Associated Press
Published: October 17, 2008

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 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, a senior scientist at the Oregon Research Institute who led the work, published in Friday’s edition of the journal Science.

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.

First, Stice’s team had to figure out how to study the brain’s immediate reactions to food. Moving inside an MRI machine skews its measurements, which ruled out letting the women slurp up the milkshakes. Yale University neuroscientist Dana Small solved that problem, with a special syringe that would squirt a small amount of milkshake or, for comparison, a tasteless solution into the mouth without study participants moving. They were told when to swallow, so researchers could coordinate the scans with that small motion.
Then they recruited volunteers, 43 female college students ages 18 to 22 and 33 teenagers, ages 14 to 18. Body mass index calculations showed the young women spanned the range from very skinny to obese.

Brain scanning showed that a key region called the dorsal striatum — a dopamine-rich pleasure center — became active when they tasted the milkshake, but not when they tasted the comparison liquid that just mimicked saliva.

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.