Binge eaters' dopamine levels spike at sight, smell of food

A brain imaging study at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory reveals a subtle difference between ordinary obese subjects and those who compulsively overeat, or binge: In binge eaters but not ordinary obese subjects, the mere sight or smell of favorite foods triggers a spike in dopamine - a brain chemical linked to reward and motivation. The findings - published online on February 24, 2011, in the journal Obesity - suggest that this dopamine spike may play a role in triggering compulsive overeating.

Brain scans comparing the effects of methylphenidate plus food stimulation to placebo plus neutral stimulation in obese binge eaters and obese control subjects who were not binge eaters. Since the radiotracer competes with the brain's natural dopamine to bind to receptors, a weaker signal from the tracer (less red) indicates more dopamine in the brain. The decrease in red in the binge eaters exposed to food and methylphenidate (lower right) compared to the placebo/neutral stimulation condition (lower left) therefore indicates that food stimulation triggered a spike in dopamine levels in these subjects. There was no difference in dopamine levels between these conditions in the non-binge eaters

''These results identify dopamine neurotransmission, which primes the brain to seek reward, as being of relevance to the neurobiology of binge eating disorder,'' said study lead author Gene-Jack Wang, a physician at Brookhaven Lab and the Mount Sinai School of Medicine. Previous studies conducted by Wang's team have identified a similar dopamine spike in drug-addicted individuals when they were shown images of people taking drugs, as well as other neurochemical similarities between drug addiction and obesity, including a role for dopamine in triggering desire for drugs and/or food.

''In earlier studies of normal-weight healthy people who had been food-deprived for 16 hours, we found that dopamine releases were significantly correlated with self-reports of hunger and desire for food. These results provided evidence of a conditioned-cue response to food,'' Wang said.

In the current study, the researchers suspected that binge-eating obese subjects would show stronger conditioned responses to food stimuli when compared with non-binging obese subjects.

''Understanding the neurobiological mechanisms underlying food stimulation might point us toward new ways to help individuals regulate their abnormal eating behaviors,'' Wang said.

The scientists studied 10 obese people with a clinical diagnosis of binge eating disorder, based on evaluations at St. Luke's-Roosevelt Hospital, and 8 obese subjects who were not binge eaters.