Published: Sat, January 12, 2019
Medicine | By Brett Sutton

Overweight people have smaller brains, study suggests

Overweight people have smaller brains, study suggests

A new study has linked carrying extra weight around the middle to a smaller brain size.

Researchers from Loughborough University and University College London discovered that people with a high body mass index (BMI) and high waist-to-hip ratio had brains that were 12 cubic cms smaller than people of a healthy weight. Based on these criteria, almost one in five of the study participants was found to be obese.

The new findings, published January 9 in the journal Neurology, suggest that the combination of obesity (as measured by body mass index, or BMI) and a high waist-to-hip ratio may be a risk factor for brain shrinkage, the researchers said.

After using a tape measure to calculate people's waist-to-hip ratio, scientists put them in MRI scanners to look at their brains.

After adjusting for other factors that may affect brain volume, such as age, physical activity, smoking and high blood pressure, researchers found that while a high BMI alone was linked to slightly lower brain volumes, those with high BMI and waist-to-hip ratios had lower gray matter brain volumes than participants who did not have a high waist-to-hip ratio.

Specifically, people with both a high BMI and high waist-to-hip ratio had an average gray matter volume of 786 cubic centimetres, compared with 793 cubic centimetres for people with a high BMI but not a high waist-to-hip ratio; and 798 cubic centimetres for people of a healthy weight. White matter contains nerve fibre bundles that connect various regions of the brain.

Dr Hamer said: 'While our study found obesity, especially around the middle, was associated with lower gray matter brain volumes, it's unclear if abnormalities in brain structure lead to obesity or if obesity leads to these changes in the brain'. Potential causes of lower brain volume Cara Bohon, an assistant professor in the Department of Psychiatry and Behavioral Sciences at the Stanford University School of Medicine, wrote in an email that the study's findings are "not particularly new or surprising". This connection between reduced brain volume and abdominal fat could suggest that inflammation and vascular factors may be at work.

While the results point to a possible association between obesity and brain volume, they do not establish that body fat necessarily causes changes in the brain.

Though the study didn't look at potential mechanisms linking visceral fat and brain shrinkage, one hypothesis is that this type of fat is thought to produce inflammatory substances that may play a role in brain atrophy, the researchers said. "Obesity can have a detrimental impact on a wide range of health parameters", he wrote.

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