Obese individuals, the scientists found, had fewer dopamine receptors than normal-weight subjects. And within the obese group, the number of dopamine receptors decreased as the subjects' body mass index, an indicator of obesity, increased. That is, the more obese the individual, the lower the number of 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," says Wang. "However, it's also possible that these people have low numbers of dopamine receptors to begin with, making them more vulnerable to addictive behaviors including compulsive food intake."
The researchers note that, based on this study alone, they cannot conclude whether the brain changes they've detected are a consequence or a cause of obesity. They also acknowledge that the regulation of body weight is extremely complex, involving many physiological mechanisms and neurotransmitters. But they do suggest that addressing the dopamine receptor deficiency or finding other ways to regulate dopamine in obese people might help reduce their tendency to overeat.
Unfortunately, many of the drugs that have been shown to alter dopamine levels are highly addictive. But exercise, which has other obvious benefits in weight control, is another way obese subjects might be able to stimulate their dopamine pleasure and satisfaction circuits, the researchers suggest. "In animal studies conducted elsewhere, exercise has been found to increase dopamine release and to raise the number of dopamine receptors," Volkow says. This suggests that obese people might be able to boost their dopamine response through exercise instead of eating just one more reason to exercise if you're trying to lose weight.
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Contact: Dennis Tartaglia
dennist@mbooth.com
212-481-7000
DOE/Brookhaven National Laboratory
31-Jan-2001