Scientists Link Dopamine Receptor, Obesity

L O N D O N, Feb. 2, 2001 -- Obese people may binge on foodjust as alcoholics or addicts abuse drink or drugs because ofdopamine, a brain chemical that produces feelings ofsatisfaction and pleasure, scientists in the United States saidtoday.

Researchers at the U.S. Department of Energy's BrookhavenNational Laboratory in New York have shown that obese peoplehave fewer brain receptors for dopamine and may eat more tostimulate the pleasure circuits in the brain.

The findings, reported in The Lancet medical journal, couldoffer a completely new approach to treating obesity, whichaffects up to a third of Americans and a growing number ofpeople around the world.

Weight-reduction programs, appetite suppressants andfat-blocker drugs have been used to combat obesity, but theBrookhaven scientists think targeting dopamine could be anotherline of attack.

"The results from this study suggest that strategies aimedat improving dopamine function might be beneficial in thetreatment of obese individuals," said Gene-Jack Wang, the leadscientist in the study.

A Reinforcing Behavior

The researchers suspected that because eating, like usingaddictive drugs, is a reinforcing behavior that brings onfeelings of pleasure, obese people might also haveabnormalities in brain dopamine.

They tested their theory on 10 extremely obese people and10 others with a normal weight. Using sophisticated brainimaging, the researchers injected into each volunteer achemical tag that binds to a dopamine receptor and thenmeasured the signal from the tags.

Strong signals indicated a high number of receptors.

"We found that obese subjects have fewer dopamine receptorsthan control subjects. This is one of the major findings," Wangsaid in a telephone interview.

"The use of food is a way to compensate for thedeficiency."

In the obese group they also noted an inverse correlationbetween body mass index and dopamine receptors thatwasn't evident in people with normal weight.

BMI is a measure of weight relative to height. It iscalculated by dividing a person's weight in kilograms by thesquare of their height in metres. A BMI of 18-25 is normal,25-30 is overweight and more than 30 is obese.

The obese people with the highest BMI had the fewestreceptors.

"It's possible that obese people have fewer dopaminereceptors because their brains are trying to compensate forhaving chronically high dopamine levels, which are triggered bychronic overeating," said Wang.

Alternatively, they could have had fewer dopamine receptorsinitially which would make them vulnerable to overeating andother addictive behaviors.

Wang and his colleagues said methods to regulate dopamine,either through drugs, exercise or behavior modification couldhelp obese people control their urge to overeat.

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