Bigger belly, smaller brain

A couple more centimetres around the waist is often followed by a worrisome list of health problems. 

Now, new research provides solid evidence linking additional body mass, especially fat around the belly, to a worrisome decrease in brain volume.

How this extra fat affects our brain function is unclear, but with previous research linking obesity to neurological conditions, it doesn't look very positive.

Let’s talk about our BMI (Body Mass Index)

BMI is determined by dividing a person's weight by the square of their height. People with a BMI greater than 30.0 are considered obese. The hip-waist ratio is determined by dividing the waist circumference by the hip circumference. People with larger bellies compared to their hips have higher proportions. Men over 0.90 and women over 0.85 are considered central obese.

"Existing research has linked brain contraction with impaired memory and an increased risk of dementia, but research on whether additional body fat is protective or detrimental to brain size has not been conclusive," explains Mark Hamer of Loughborough University in Leicestershire, England, and a leader of the work. "Our research examined a large group of people and found that obesity, specifically in the belly, may be linked to brain contractions.

The study evaluated 9,652 people with an average age of 55 years. Of that group, 19% were determined to be obese. Researchers measured BMI, waist-hip ratio, and overall body fat, and surveyed participants about their health. The researchers then used magnetic resonance imaging to determine brain volumes of white and gray matter in different regions of the brain.

Gray matter consists of most of the brain's nerve cells and includes regions of the brain involved in self-control, muscle control and sensory perception. White matter consists of bundles of nerve fibers that connect various regions of the brain.

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

Specifically, the researchers found that 1,291 people with a high BMI and a high waist-hip ratio had the lowest average gray matter brain volume (786 cubic centimeters), compared with 3,025 healthy-weight people who had an average gray matter brain volume of 798 cubic centimeters. 514 people with a high BMI but without a high waist-to-hip ratio had an average gray matter brain volume of 793 cubic centimeters. They found no significant differences in the brain volume of white matter.

"While our study found that obesity, especially in the environment, was associated with lower volumes of gray matter in the brain, it's not clear whether abnormalities in brain structure lead to obesity or whether obesity leads to these changes in the brain," Hamer said. "We also found links between obesity and contraction in specific regions of the brain. This will require more research, but it may one day be possible to regularly measure BMI and waist-hip ratio to help determine brain health.

One limitation of the study was that only 5% of those invited to participate in the study participated, and those who participated tended to be healthier than those who did not, so the results may not reflect the population as a whole.

Reference: Neurology