Overweight people are less intelligent than people who are do not have weight problems , a provocative study claims.
Overweight men and women have less grey and white matter in key areas of the brain, it suggests. They also have greater impulsiveness and “altered reward processing”, the study said.
The researchers said that their findings could explain why overweight people make poor diet choices – they do not have the mental capacity to control themselves.
The theory is likely to prove controversial as weight loss campaigners have emphasised that the issues behind weight problems vary from individual to individual.
The research involved sophisticated brain images of 32 adults – 16 men and 16 women – selected from the US city of Baltimore, in Maryland.
Anyone who had a history of brain damage, substance abuse or mental illness was excluded from the group.
The researchers measured Body Mass Index, a commonly-used measure of how overweight a person is, and body fat percentages and compared them to differences in brain structure and function.
He said they covered changes across the whole brain, but also “specific networks”.
In particular he was interested in the “salience network”, which he described as the “seat of motivation, willpower, and the ability to persevere through physical and emotional challenges”.
The results showed that there was “no significant difference” in terms of white matter between people who had a normal weight and people who were overweight.
In a surprise twist, people with a higher BMI actually had slightly more grey matter overall.
However, looking at specific networks on the brain a different picture began to emerge. In particular, heavier and fatter people had less white matter in the salience network.
There were also differences in the dorsal striatum, an area of the brain involved with habitual behaviour.
Professor Figley told the National Post, a Canadian newspaper: “It stands to reason that these changes could further affect the ability of overweight individuals to exert self-control and maintain healthy lifestyle choices.”
He added that it was not clear if the brain differences predispose certain individuals to becoming fat, or vice versa.
However, he said: “There are previous studies that imply elevated body fat can cause these sorts of brain changes.”
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The study was reported in the journal Frontiers in Neuroscience.