Excess body fat around the abdomen has been linked to having a smaller brain in a study which asks whether cutting rates of obesity could also help prevent neurodegenerative diseases like dementia.
Dr. Mark Hamer of Loughborough University in Leicestershire, U.K., who authored the research published in Neurology, explained in a statement that existing studies have linked brain shrinkage to memory problems and a higher chance of developing dementia, of which Alzheimer’s disease is the most common.
To investigate whether a person’s weight could affect the size of their brain, the team studied data on 9,652 people. The participants were aged between 40 to 69 years old, with an average age of 55. Almost a fifth of these participants were classed as obese.
In the study, obesity was determined by an individual’s body fat percentage, BMI, as well as the ratio of their waist to hip measurements. BMI (body mass index) is an individual’s weight in kilograms divided by their height in meters. The figure is used to predict whether a person has a high body fat percentage, with a score of 30 or more indicating obesity.
The volunteers were asked questions about their health and lifestyle factors, like whether they smoked or exercised; their educational attainment; and blood pressure.
Researchers used MRI scanners to document participants’ brains, including levels of gray matter (where the majority of the organ’s cell bodies are) and white matter (which largely links up different parts of the brain).
The study revealed that participants with the highest BMI and waist-to-hip ratio had the lowest volumes of gray matter, at 786 cubic centimeters on average. In contrast, those with a high BMI but not a high waist-to-hip ratio had an average of 793 cubic centimeters of gray matter. And those with a healthy weight had an average of 798 cubic centimeters of gray matter. The volume of white matter didn’t change depending on an individual’s weight.
“[We] found obesity, specifically around the middle, may be linked with brain shrinkage,” Hamer said. “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.”
However, Hamer cautioned the study does not prove belly fat causes the brain to reduce in size. The authors also admitted their research had limitations, as all studies do. In this instance, those who took part were more likely to be healthy than those who didn’t choose to, the authors wrote.
“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,” he said.
And while BMI is a useful tool to quickly predict whether the average person’s body fat percentage is too high, it is not foolproof. A short bodybuilder, for instance, may have a high BMI but low levels of body fat.
Last year, researchers behind a separate study proposed a new method for determining whether a person’s body weight is dangerously high. In their paper published in the journal Advances in Genetics, they argued measuring the metabolome—which is comprised of molecules such as glucose—could provide a more accurate picture of a person’s health.
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