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Overeating? Blame Your Genes

THURSDAY Oct. 16, 2008 -- A gene could help prod people to overeat and gain excess weight, new research shows.

The finding probably won't provide a "magic bullet" for weight loss, but it does reinforce the value of good eating habits and exercise, especially for young people, scientists say.

The study, reported in the Oct. 17 issue of Science, is the latest in a series focusing on the brain's response to food using the neurotransmitter dopamine. Cells in the brain's "reward" centers release dopamine when people eat, causing that feeling of pleasure, researchers explain.

Previous studies have shown that some people have fewer brain cell receptors for dopamine, which leads them to eat more to gain the same pleasurable effect. The new study used scans of the brain pleasure centers of a group of women. They revealed a sluggish dopamine response in the brains of some of the women.

"This is the first imaging study which found less activation of dopamine receptors in [some] humans," said study lead author Eric Stice, a scientist at the Oregon Research Institute in Portland.

Women with one form of the D2 dopamine receptor gene had the lowest pleasure response when drinking a milkshake, the scans showed. They had to consume more of the shake to get the same pleasure response. Follow-up study found that these women were also more likely to gain weight over the following year.

The study was done in collaboration with researchers at Yale University and the University of Texas at Austin.

"What is new here is that for the first time they have identified the consequences of this genetic polymorphism [type] in how the brain functions," said Dr. Nora Volkow, who worked on earlier studies at Brookhaven National Laboratory that established the role of the D2 gene in overeating. She is now is director of the U.S. National Institute on Drug Abuse.

Volkow noted that prior studies had linked this form of the gene to obesity, and the new work "shows an association in the brain region that governs pleasure. The response is different with this polymorphism."

Studies of obese animals at Brookhaven National Laboratory have shown that dieting increases the D2 response to food, according to Peter Thanos, a neuroscientist at the lab. "If we could identify people who are more vulnerable, it would be fascinating to see what effect dieting has on their risk in terms of brain response," Thanos said. "No one has really done this in humans."

Diet pills aimed at the dopamine receptors won't work, Stice said. "These amphetamine-based diet pills are not the way to go," he said. Instead, Stice advocates early behavioral intervention that steers children away from fatty fast foods. "You want to change people's behaviors before they become entrenched," he said.

Exercise shouldn't be overlooked, Volkow added.

"Dieting is a complex process and people don't like it," she said. "Physical activity, which also activates the dopamine pathway, may be a mechanism for reducing the compulsive activity of overeating."

This work on obesity meshes nicely with drug-abuse studies, noted Volkow, who retains her laboratory position at Brookhaven. Both are instances of people engaging in compulsive behaviors, "even though they know it is very harmful," she said

More information

There's more on dopamine at the University of Texas at Austin.

Posted: October 2008


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