A study conducted by researchers at Loughborough University has found that excess abdominal fat is associated with a lower volume of gray matter in the brain.
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Professor of exercise, Mark Hamer, and colleagues found that a higher body mass index (BMI), together with a higher waist-to-hip ratio, was linked to a lower gray matter volume, when compared to leaner individuals.
Interestingly, a higher BMI, together with an average waist-to-hip ratio, was not associated with any significant reduction in gray matter volume.
BMI is a general measurement of body weight compared to height, meaning taller individuals or those with more muscle mass may have a high BMI, even if they are lean. Abdominal fat, on the other hand, indicates how much visceral fat may be surrounding abdominal organs such as the liver and intestines. This visceral fat can have toxic effects by triggering inflammation that can drive conditions such as arthritis and heart disease.
As reported in the journal Neurology, Hamer and team studied brain images available for 9,652 people (aged an average of 55 years) who had their BMI and waist-to-hip ratios measured between 2006 and 2010. The subjects were enrolled in the UK Biobank study, which includes information from volunteers who regularly update their medical information.
A healthy BMI is defined as a score between 18.5 and 24.9, while a score of 30 or higher is defined as obese. The waist-to-hip ratio score is considered high and indicative of central obesity if it is above 0.90 for men and above 0.85 for women.
The researchers found that people who had a higher BMI combined with a higher waist-to-hip ratio had a lower grey matter volume (average of 785cm3) than individuals with a healthy BMI and waist-to hip ratio (average of 798 cm3). This effect was observed after adjustment for factors such as age, smoking history, physical activity, education level and a history of poor mental health.
However, people who had a higher BMI, but a healthy waist-to-hip ratio, had a similar gray matter volume to those with both a healthy BMI and waist-to hip ratio, at an average of 793cm3.
"The reductions in brain size increase in a linear fashion as fat around the middle grew larger," writes Hamer.
The results support the evidence that staying lean has beneficial health effects, not just by decreasing the risk of heart-related problems, but possibly by maintaining a healthy brain as well.
Hamer points to recently published research demonstrating how exercise can increase gray matter volume and may represent a way of counteracting some of the negative impacts obesity may have on the brain and body:
The take-home message is that being overweight and obese has a multitude of effects on health, so it’s unsurprising that obesity is also going to have an effect on our brain health.”
Professor Mark Hamer, Lead Researcher