Losing weight is not only good for the waistline, it is good for the brain.
Scientists say substantial weight loss improves cognitive functions like memory and concentration.
Researchers carried out tests on 150 volunteers, all weighing over 21 stone, and compared them with results from healthy people.
In some tests, including memory exams, almost a quarter of the overweight participants scored low enough to be considered learning disabled.
Many of them had additional health problems, such as high blood pressure, type two diabetes and sleep apnea.
After the initial round of testing, two-thirds of the volunteers had gastric bypass surgery to reduce the size of the stomach and lost an average of about 3st 8lbs.
After 12 weeks, they all took the tests again and the group that lost weight boosted their scores, particularly those involving memory, significantly. They also showed great improvement in organisational skills.
The 41 obese volunteers who declined the surgery ended up with even worse results.
Professor John Gunstad, of Kent State University, Ohio, said the research showed obesity can damage the brain, ‘especially the parts most important for paying attention and learning new things’.
In the study the researchers also used magnetic resonance imaging to see inside their subjects’ brains.
The obese subjects tended to have damage to a particular substance that surrounds and insulates nerve fibres in the brain, suggesting that substance is needed for optimal cognitive function.