New UK research has found that carrying extra body fat, especially around the waist, may be linked to a smaller brain size, which could indicate a higher risk of dementia.
Carried out by researchers at Loughborough University, the new study looked at 9,652 adults with an average age of 55, and used magnetic resonance imaging (MRI) to measure brain volumes for white and gray brain matter.
To looked at the possible effect of carrying extra weight on these brain volumes, the researchers determined participants' obesity by measuring body mass index (BMI), a weight-to-height ratio calculated by dividing a person's weight by the square of their height. People with a BMI above 30.0 are considered obese.
They then measured the participants' waist-to-hip ratio, determined by dividing waist circumference by hip circumference. People who have bigger bellies compared to their hips have a higher ratio, with men above 0.90 and women above 0.85 considered to be centrally obese.
The findings, published in the journal Neurology, showed that after adjusting for other factors that may affect brain volume, such as age, physical activity, smoking and high blood pressure, participants with a high BMI had a slightly lower grey matter volume than those with a healthy BMI.
However, those with both a high BMI and high waist-to-hip ratio had an even lower gray brain matter volume than participants who did not have a high waist-to-hip ratio.
No significant differences were found in white matter brain volume.
"Existing research has linked brain shrinkage to memory decline and a higher risk of dementia, but research on whether extra body fat is protective or detrimental to brain size has been inconclusive," said study author Mark Hamer, PhD. "Our research looked at a large group of people and found obesity, specifically around the middle, may be linked with brain shrinkage."
Gray matter contains most of the brain's nerve cells and includes brain regions involved in self-control, muscle control and sensory perception. White matter contains nerve fiber bundles that connect various regions of the brain.
"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," said Hamer. "We also found links between obesity and shrinkage in specific regions of the brain. This will need further research but it may be possible that someday regularly measuring BMI and waist-to-hip ratio may help determine brain health."