Hungry? Drop that Milkshake.

Milkshakes paved they way for the latest study on obesity. A group of women were asked to drink a pleasurable food (a chocolate milkshake) and a control mixture (a tasteless liquid) while scientists measured their brain activity with an fMRI machine. This was the first time that researchers studied the effects of food while the subjects actually consumed it. They found that obese women showed less activity in the dorsal striatum, the area of the brain that is the hub of dopamine, when they drank the milkshake compared to that of their leaner counterparts. A lack of pleasurable stimulation occurred while they drank. And when researchers followed up with their participants a year later, the women who gained weight were those with decreased activity in that section of the brain. 

This seemingly illogical occurrence was consistent in all the women participating in the study. The obese women consumed more food, not because they enjoyed it more, but because they enjoyed it less. It was a form of compensation that boiled down to quantity over quality to their brains. "If you ask overweight individuals if they crave food, I really think they are legitimately thinking it is more rewarding," says study author Eric Stice, a senior scientist at the Oregon Research Institute. "They'll say they're really sensitive to the rewards. But when you look at the brain scans you get a different picture." 

This reinforces the idea that obesity is more similar to a drug addiction that was once believed. Dopamine, a critical part of addiction research, was shown to have similar patterns in brains of women that received less pleasure when drinking their milkshakes. "This research follows what we have seen in addictive people," says Nora Volkow, director of the National Institute on Drug Abuse. "At first we thought they were more sensitive to pleasurable responses. But research has shown exactly the opposite, that they have a blunted response to drugs and release much less dopamine. With obesity, it took everyone by surprise."

The majority of the women who were dissatisfied by their milkshakes had a variation of the Taq1A1 allele. "What this research does to move things forward is identify a genetic component to brain functioning in obese people," says Gene-Jack Wang, a scientist with the Brookhaven National Laboratory. "This is a gene that can go any direction and these people are potentially more vulnerable [to having lower levels of dopamine]." Having a genetic predisposition to be less sated by food could lead to new methods of obesity prevention; however it is still infeasible at this time to genotype for fitness. 

Article from Newsweek: http://www.newsweek.com/id/164197