He found that obese individuals had more water in the amygdala – a part of the brain involved in eating behaviour. He also saw smaller orbitofrontal cortices in obese individuals, important for impulse control and also involved in feeding behaviour (Brain Research, in press). “It could mean that there are less neurons, or that those neurons are shrunken,” says Convit.

Eric Stice at Oregon Research Institute, Eugene, thinks that the findings strengthen the “slippery slope” theory of obesity. “If you overeat, it appears to result in neural changes that increase the risk for future overeating,” he says. Obesity is associated with a constant, low-level inflammation, which Convit thinks explains the change in brain size.