WASHINGTON, Oct 17: Drink a milkshake and the pleasure centre in your brain gets a hit of happy — unless you are overweight.

It sounds counter-intuitive. But US scientists who watched young women savour 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 harboured 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.

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 is 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.

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.

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