Drink a milkshake and the pleasure
center in your brain gets a hit of happy — unless you're
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
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.
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. What is it doing to the way the
brain is functioning that would make a person more vulnerable
to compulsively eat food and become obese?"
It's "very elegant work," she added.
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
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.
Regardless, most people's tongues find a milkshake quite
tasty; the brain reaction is subconscious.
But if doctors could determine who carries the at-risk gene,
children especially could be steered toward "recreational
sports or other things that give them satisfaction and pleasure
and dopamine that aren't food ... and not get their brains
used to having crappy food," said Stice, a clinical psychologist
who has long studied obesity.
"Don't get your brain used to it," he said
of non-nutritious food. "I would not buy Ho Hos for lunch
every day because the more you eat, the more you crave."