Overcoming Obesity

For dieters, it's sometimes impossible to resist your favorite foods. Like chocolate. And now some researchers working with mice think they have a clue as to why the temptation can get so strong.

After starving mice of food, scientists presented them with a highly desirable treat of chocolate — in an experiment designed to keep them from getting it. Each time the animals went for the sweet, they received a small foot shock. One group of starving mice learned to stop reaching for the chocolate after a few shocks, but another group went for the candy relentlessly, despite the negative consequences.

The difference between the two groups seemed to be levels of norepinephrine, a hormone and neurotransmitter released in the prefrontal cortex of the brain, which is involved in reward and satiety circuits. Norepinephrine plays an important role in compulsive behaviors associated with drug abuse, and also contributes to food-seeking behavior. In the chocolate trial, the treat-seeking mice had higher levels of norepinephrine than the mice who abandoned the chocolate. And when scientists used an inhibitor to inactivate the chemical in the chocolate-obsessed animals, their compulsive behavior stopped.

Doctors hope that by understanding the way biological processes reinforce maladaptive behaviors like obsessive eating, they can focus on new targets for treating obesity — targets that directly address the root causes of why some people continue to eat, even when they know they shouldn't.