It was previously thought individuals who overeat are compensating for a lack of pleasure hormones in the brain. But new research suggests their 'reward centre' is already stimulated before eating - and obesity may thus be a result of an active brain.
Eating certain foods produces dopamine - the pleasure hormone - and the degree of pleasure from eating correlates with the amount of dopamine release.
Studies have shown overweight people generally have fewer dopamine (D2) receptors in the brain and it is thought that obese individuals overeat to compensate for this reward deficit.
But a report published in The Journal of Neuroscience showed how functional Magnetic Resonance Imaging (fMRI) showed the neural response to food and monetary reward in lean adolescents at risk for obesity suggested their brains were more sensitive, with increased activity in the 'reward circuitry'.
"The findings are surprising," the research team said. "They suggest that the initial vulnerability for overeating may be hyper-responsivity of reward circuitry to food intake.
“The fact that the same reward regions showed greater response to monetary reward is novel and implies that individuals at risk for obesity show greater responsivity to reward in general. These findings seem to challenge the widely accepted theory that it is a reward deficit that increases vulnerability to overeating."