Like Drug Addicts, Obese People Have Paltry Pleasure Pathway

Like compulsive gamblers and drug addicts, overeating may be a way people make up for a faulty reward circuit in the brain.

Using sophisticated imaging devices, researchers from Upton, N.Y.'s Brookhaven National Laboratory report in the Feb. 3 issue of The Lancet that obese people have fewer brain receptors for an important brain chemical. The chemical, dopamine, stimulates the brain's reward center to produce feelings of satisfaction and pleasure. People addicted to drugs such as cocaine or amphetamines also have poor dopamine circuits in their brains.

"Obese people share many behaviors extremely similar to those of the drug addict -- they have an inability to control food intake and an inability to control craving that is similar to what we see in drug addiction," research team leader Nora D. Volkow, PhD, tells WebMD. "What we found was obese people -- like drug addicts -- have a decline in dopamine receptors, which transmit dopamine signals into the brain. [Our theory is] this perpetuates the consumption of food because food increases dopamine release in the brain."

It's not yet known whether overeating is a cause or an effect of dopamine dysfunction. To answer this question, Volkow says her team currently is performing a before-and-after study on obese patients undergoing a procedure called stomach ligation to restrict the size of the stomach.

For many years it was thought that people who become addicted to drugs get more pleasure from the drugs than normal people. Volkow's team has suggested that just the opposite is true: addicts get less pleasure from drugs and everything else. Thus drug abuse -- and, now, perhaps overeating -- can be seen as a desperate and misguided effort to compensate for abnormal brain function.

"Your brain motivates you by activating either reward or aversive circuits," Volkow says. "Normally you need those reward circuits to be activated. If the reward systems are not activated, [negative] signals prevail and you feel anxious and distressed. Your brain is saying 'do something to get out of this.' That is why some people take drugs. And food may be another way to escape that state. Why some people choose food or drugs or gambling or sex involves many things -- there must be cultural, developmental, and emotional components -- but common among them is disruption of dopamine signaling. This leads to reduced sensitivity to reward pathways, which makes people act in compulsive ways to overcome these feelings of dissatisfaction."

Amphetamines -- now known to be dangerous drugs on which people can become dependent -- originally were used as diet aids. Now it is know that these drugs increased brain levels of dopamine. Because ever-greater doses are needed to maintain weight loss, such drugs cannot be used to treat obesity without causing severe damage to a person's health.

So what's the answer? Even though the explanation for obesity may be new, the solution is the same: exercise.

"By exercising you make the dopamine circuit more active," Volkow says. "Exercise has a direct effect on these same molecules we find to be abnormal in obese people. So exercise may be able to decrease weight not only by burning calories but also by improving dopamine pathways to make these people more sensitive to being rewarded by things other than food."

Laurey R. Simkin-Silverman, PhD, is principal investigator for the Primary Care Weight Control Project at the University of Pittsburgh Graduate School of Public Health. She says that the idea of overeating as an addiction may or may not be entirely accurate -- but she says Volkow's solution is accurate.

"Exercise is what is currently recommended for obesity, because we know it is one of the essential components of an effective weight-control program," she tells WebMD. "Exercise also has a link to alleviating mild depression. Exercise, dietary changes, and behavioral modification are the three critical things."

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