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Why obese people overeat: A clue in the brain

October 16, 2008 | 11:35 am

Milkshake1Obese people may overeat because they don't feel the satisfaction from eating that normal-weight people do, say the authors of a paper in today's issue of Science.

There is something very intuitive about this. We eat for sustenance and for pleasure. The term "comfort food" describes this connection between food and mood. But if a few chocolate chip cookies just aren't doing it for you, perhaps a few more will, and a few more after that.

That's the essence of the discovery made by researchers at the Oregon Research Institute, University of Texas, Yale University and the John B. Pierce Laboratory. The scientists found that people who experience weaker activity in the reward circuitry areas of the brain while eating are more likely to be obese and more likely to gain weight over time. The effect is even greater for people with a gene variation that is associated with weaker dopamine signaling in the brain. Dopamine is the primary neurotransmitter involved in the brain's reward pathways. It is released in response to eating, and the amount released corresponds to the degree of pleasure the food brings.

The researchers conducted two studies examining young women, some of whom were obese. Most of the participants were tested for the gene variation called Taq1A1 that is linked to decreased dopamine signaling. Brain scans conducted of the participants while they drank a chocolate milkshake showed a much lower response in the brains of the obese women. After a year, the women with this blunted response and who possessed the gene variation gained more weight than women with a stronger response to the milkshake.

The study demonstrates "an association between an abnormal response to food and future weight gain -- and it shows that this relationship depends upon your genetic makeup," said one of the researchers, Dana Small, an associate professor at Yale.

Armed with this knowledge, researchers may be able to find a behavioral or drug treatment that addresses or corrects this reward deficit in the brain among people prone to obesity, said Eric Stice, senior scientist at the Oregon Research Institute and the study's lead author.

-- Shari Roan

Photo credit: Lori Shepler / Los Angeles Times