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REWARD pathways in the brains of overweight people become less responsive as they gain weight. This causes them to eat more to get the same pleasure from their food, which in turn reduces the reward response still further.

, 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…