Scientists Link Dopamine Receptor, Obesity

Obese people may binge on food just as alcoholics or addicts abuse drink or drugs because of dopamine, a brain chemical that produces feelings of satisfaction and pleasure, scientists in the United States said today.

Researchers at the U.S. Department of Energy's Brookhaven National Laboratory in New York have shown that obese people have fewer brain receptors for dopamine and may eat more to stimulate the pleasure circuits in the brain.

The findings, reported in The Lancet medical journal, could offer a completely new approach to treating obesity, which affects up to a third of Americans and a growing number of people around the world.

Weight-reduction programs, appetite suppressants and fat-blocker drugs have been used to combat obesity, but the Brookhaven scientists think targeting dopamine could be another line of attack.

"The results from this study suggest that strategies aimed at improving dopamine function might be beneficial in the treatment of obese individuals," said Gene-Jack Wang, the lead scientist in the study.

A Reinforcing Behavior

The researchers suspected that because eating, like using addictive drugs, is a reinforcing behavior that brings on feelings of pleasure, obese people might also have abnormalities in brain dopamine.

They tested their theory on 10 extremely obese people and 10 others with a normal weight. Using sophisticated brain imaging, the researchers injected into each volunteer a chemical tag that binds to a dopamine receptor and then measured the signal from the tags.

Strong signals indicated a high number of receptors.

"We found that obese subjects have fewer dopamine receptors than control subjects. This is one of the major findings," Wang said in a telephone interview.

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

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

BMI is a measure of weight relative to height. It is calculated by dividing a person's weight in kilograms by the square 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 fewest receptors.

"It's possible that obese people have fewer dopamine receptors because their brains are trying to compensate for having chronically high dopamine levels, which are triggered by chronic overeating," said Wang.

Alternatively, they could have had fewer dopamine receptors initially which would make them vulnerable to overeating and other addictive behaviors.

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