the brains of morbidly obese women contained fewer μ-opioid receptors available for binding than the brains of women of normal weight. These receptors allow people to feel the intense rushes of pleasure that come with activities from eating to using heroin.
“If there is insufficiency in [the food reward processing] system, the compensation would be to reach the pleasurable level [by eating] a little more,”
…as people increase their caloric intake, their response to opioids lessens. Perhaps this spurs them to overeat even further, in hopes that the pleasurable sensations will return…revealing a weight-dependent pattern…significantly fewer μ-opioid receptors in the brains of morbidly obese women than in the brains of women of healthy weight, particularly in brain areas involved in reward…the number of μ-opioid receptors decreased in the morbidly obese women…The morbidly obese women had normal dopamine receptor availability.
The finding “is consistent with addiction biology in general—where excess stimulation via addictive substance causes increased neurotransmitter secretion…[The] number of neuroreceptors decrease[s] in response.”…..bariatric surgery normalizes μ-opioid receptors.