Obese people are known to have a less sensitive reward centre in the brain, which drives them to overeat. This may, in turn, further dampen their reward circuitry for food.

Eric Stice at the University of Texas at Austin and his co-workers used functional magnetic resonance imaging to scan the brains of 20 overweight female volunteers of similar body mass index (BMI) as they sipped either a chocolate milkshake or a tasteless solution. The researchers repeated the tests six months later. They found that women who had a greater than 2.5% increase in their BMI over the interim period showed a reduced response in the brain's striatum to the milkshake relative to their baseline response, as well as to women whose weight had remained steady over the six-month period.

J. Neurosci. 30, 13105–13109 (2010)