Can't Control Your Appetite? Here's Why

Researchers discover why it's so difficult to knock off those extra pounds.

ByABC News
October 7, 2008, 7:27 PM

Oct. 8, 2008— -- Want another reason why you shouldn't spend too much time at the trough? Because consistently eating too much food over a period of just a few weeks can screw up your brain, taking away your ability to control your appetite.

That's the basic finding in a new study out of the University of Wisconsin-Madison that could help explain why once you've put on those extra pounds, it's really hard to take them off. The study is published in the current issue of the journal Cell.

"We've discovered why the appetite doesn't shut down," said Dongsheng Cai, assistant professor of physiology at UW-Madison, in a telephone interview, even after a person has consumed enough food to maintain the correct balance between calorie intake and energy expended.

The answer lies in a normally inactive "pathway" through a critical part of the brain that springs to life after at least a couple of months of "overnutrition," he said. A pathway is a course by which brain cells transmit impulses from their origin to their destination. But in this case, a normally dormant pathway is re-energized and interferes with "signaling" that should tell the brain you've had enough to eat.

"We're not talking about one day, or even a few days" of overeating, Cai said. "It's not too long. Two or three months of overnutrition, a diet high in fat and sugar," can wake up the pathway, he said.

Once the pathway is mobilized, he said, it can "lead to a number of dysfunctions, including resistance to insulin and leptin." Leptin is a fat hormone essential for appetite control. Insulin lowers blood sugar by causing cells to extract it from the bloodstream. Both are critical to maintaining the balance between caloric intake and energy expenditures.

The good news is it may be possible to shut down that apparently obsolete pathway in the brain, thus restoring an obese person's ability to control his or her appetite. It's significant that the activation of the pathway preceded obesity in lab mice, so it is clearly part of the cause of weight gain, not just the result.