People with severe weight problems sometimes say their cravings for food feel as powerful as those caused by narcotics. Researchers at Brookhaven National Laboratory in New York believe it. Their recent study shows that drug addicts and the chronically obese share a similar shortage of receptors for dopamine, one of the brain chemicals that help stimulate feelings of pleasure.
Physician Gene-Jack Wang and psychiatrist Nora Volkow of Brookhaven, along with their colleagues, injected a mixed group of obese people and those of normal weight with a radioactive chemical that binds to dopamine receptors, then examined the subjects' brains with PET scans. Obese people had fewer receptors overall, and the disparity increased with a higher body-mass index. The same researchers had previously observed a similar paucity of dopamine receptors in scans of the brains of drug addicts.
As with cocaine or heroin, eating causes the body to produce dopamine. In normal brains, routine pleasures such as watching a sunset also release the chemical. Researchers hypothesize that brains containing fewer receptors are less sensitive to everyday joys. "It's like living your life in gray," says Volkow. "If other stimuli aren't powerful enough to activate those reward circuits, you're going to get something that will, and food will do it." Drugs that boost the production of dopamine show promise of breaking the cycle of overeating in animal tests. Such treatments are far from FDA approval, however, and Volkow cautions that human behavior may limit their efficacy. For now, she recommends a familiar but proven alternative: exercise, which not only releases dopamine but seems to increase the number of receptors over time.
