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May 23, 2002 -- Just seeing and smelling food triggers an increase in a brain chemical that makes you hungry. It's the same signal that makes drug addicts want more drugs, suggesting that this may be the mechanism behind food addiction, a new study shows.

The signal is dopamine, a powerful brain chemical that lies at the heart of addiction. Dopamine is an important part of the brain's pleasure and reward machinery.

Addictive drugs increase brain levels of dopamine. Compared with normal people, addicts have fewer dopamine receptors -- the pleasure switch that high levels of dopamine flips on (to heighten the feelings of pleasure and reward.) Studies at the U.S. Department of Energy's Brookhaven National Laboratory show that obese people also have few dopamine receptors.

Now a research team led by Brookhaven's Nora Volkow, MD, finds that people don't actually have to eat to get a surge of dopamine. It happens when they just see, smell, and have a tiny taste of food. This makes them even hungrier.

The study is published in the June 1 issue of the journal Synapse.

"Eating is a highly reinforcing behavior, just like taking drugs," Volkow says in a news release. "This is the first time anyone has shown that the dopamine system can be triggered by food when there is no pleasure associated with it, since the subjects don't eat the food. This provides us with new clues about the mechanisms that lead people to eat other than just for pleasure. This may help us understand why some people overeat."

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