Vital brain region is thinner in obese children than their skinnier peers

Primary school children who are overweight may have poorer thinking skills, a study suggests.

Children aged nine to 11 were found to do worse in problem-solving and memory tests if they were obese or overweight.

A study of 2,700 children also found those who were overweight had a thinner cortex – the brain region important for reasoning.

Similar structural brain changes are seen in middle-aged people as they get older.

However, while overweight youngsters did worse than lean ones in tests of thinking skills and had less grey matter in their cortex, the cause is still unclear.

A fatty diet may cause damaging inflammation at a time when a child’s brain is still developing.

But another theory is that children had different brains before they became obese, which made fatty and sugary foods more rewarding and reduced their willpower, while also affecting their thinking abilities.

The study, led by the University of Cambridge, involved US children asked to do tests including remembering a list of animals in size order and spotting matching patterns.

Lean children scored almost six points higher than obese children, and almost four points higher than those who were overweight on average.

The tests are designed to measure ‘executive function’, which includes short-term memory and decision-making.

Dr Lisa Ronan, first author of the study from Cambridge’s department of psychiatry, said: ‘The study shows reduced executive function in obese and overweight children, which might suggest they would struggle with planning, problem-solving and regulating emotions.

‘That could affect their performance at school, but not every child who is overweight will have these brain changes and test results, so the results cannot tell us much about the real world.

‘It may be the case that the changes in brain structure come before obesity, or that shared genes cause both.’

Almost one in five children in the UK are overweight or obese when they start primary school, putting them at greater risk of diabetes, heart disease and cancer in later life.

The latest study is one of the largest to look at children’s BMI (body mass index) and their thinking skills and brains.

Researchers found heavier children did worse on tests of executive function, even when factors like their age and economic circumstances were taken into account.

Looking at MRI scans of the children’s entire brains, they found those who were most overweight had a thinner cortex – the ‘grey matter’ which makes up the outer layer of the brain.

The results, published in the journal Cerebral Cortex, found that a thinner cortex, particularly the pre-frontal cortex at the front of the brain, meant worse test results, and vice versa.

The findings raise concern for obese children, as problems with thinking skills in childhood tend to continue through to adulthood.

If being overweight causes brain changes, that might explain why obese adults who have weight loss surgery develop better cognitive abilities.

However children with poor thinking skills may also have had them before they put on weight.

That is because executive function affects not only working memory but also the brain’s reward pathway, which might make food more desirable, and children’s impulsiveness, which might cause them to overeat.

The study will follow the children over time to see if losing weight improves their test results.

Professor Paul Fletcher, senior author of the study from the University of Cambridge, said: ‘The findings contribute a small part towards our growing understanding of the causes and consequences of obesity in children.’