Reward pathways in the brains of overweight people become less responsive as they gain weight, the New Scientist reports.
This causes them to eat more to get the same pleasure from their food, which in turn reduces the reward response still further.
Eric Stice, a psychologist at the University of Texas at Austin, and colleagues used fMRI brain scans to monitor 26 obese or overweight volunteers as they sipped either a tasty milkshake or a flavourless liquid resembling saliva.
They compared the effect of both drinks on brain activity in the dorsal striatum, a key part of the brain's reward circuitry. Six months later, they retested the volunteers.
Those who had gained weight since the first test also showed reduced activity in the dorsal striatum in response to the milkshake. In contrast, no change was seen in people who had lost or maintained weight (Journal of Neuroscience).
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The result suggests that overeating may push people onto a slippery slope akin to a drug addict's craving for ever-larger doses.
"People are having to eat more and more to chase the high," says Stice. It remains to be seen whether losing weight can reverse the cycle and restore normal functioning of the reward pathway.
