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, 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.”
Hamer told Newsweek he hopes the study will help with the early diagnosis and prevention of neurodegenerative diseases.
However, he 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. Hamer told Newsweek: “The sample was generally healthy and more affluent, and may not be widely representative.”
“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.
Asked what the takehome message of the study was, he told Newsweek: “As well as maintaining a healthy weight, we should encourage people to be physically active, not smoke, drink in moderation, eat a healthy diet, and keep blood pressure and cholesterol in check in order to keep risk of dementia as low as possible.”
Dr. Claire Steves, senior clinical lecturer at King’s College London, U.K. who did not work on the study, told Newsweek: “This paper highlights the importance of considering overall health in the development of cognitive ageing and dementia.”
She explained: “It’s increasingly apparent that whole body metabolism and inflammation play a role in neurodegeneration. These have both been associated with the central obesity highlighted in this study. Understanding these relationships is ever more important given the rise in abdominal obesity in the population as a whole.”
Dr. James Pickett, head of research at Alzheimer’s Society who was not involved in the research, commented in a statement: “We know there’s a link between obesity and dementia, so it’s not hugely surprising to see the results of this study showing obese people had slightly less grey matter, a risk factor for dementia.
“We don’t know what precisely links obesity, brain health, and risk of dementia, but it is likely that poorer cardiovascular health plays a role. Just going for a brisk walk and cutting down on the sugary snacks will help lower your chances of dementia.”
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.