More than 300 million people worldwide are considered obese, according to the World Health Organization. Obesity has long been known to increase one’s risk of developing a number of chronic diseases such as high blood pressure, heart disease, type 2 diabetes and stroke, though its effect on the brain has not been clear.
Dr. Paul Thompson, senior author of the study and professor of neurology at the University of California at Los Angeles (UCLA), noted that these percentages are “a big loss of tissue.”
Thompson, lead author Cyrus A. Raji, a student of medicine at the University of Pittsburgh School of Medicine, and colleagues examined the brain images of 94 people aged 70 and over who had taken part in another study called the Cardiovascular Health Cognition Study.
All the subjects were healthy and were assessed as having suffered no cognitive impairment in the five years following the time the scans were taken. Their body mass index (BMI) was also measured, and they were categorized as either obese, overweight, or normal weight. BMI is defined as the ratio of a person's weight in kilos to the square of their height in metres. A BMI of 18.5 to 25 is normal, 25 to 30 is overweight, and over 30 is considered obese.
The brain scans were converted into 3-D images using tensor-based morphometry, a high-resolution method of showing detailed anatomy of the brain. Using these images, researchers were able to determine which parts of the brain were most affected by examining the both the grey and white matter.
The researchers found that the obese subjects had lost brain tissue in those areas of the brain important for planning and memory (the frontal and temporal lobes), attention and executive functions (the anterior cingulate gyrus), long-term memory (the hippocampus), and movement (the basal ganglia).
Overweight participants showed brain tissue loss in the basal ganglia, the corona radiata, the white matter, and the parietal lobe.
Even when taking into account age, gender and race, the findings were consistent.
"The brains of obese people looked 16 years older than the brains of those who were lean, and in overweight people looked 8 years older," Thompson said. Obesity “depletes your cognitive reserves, putting you at much greater risk of Alzheimer's and other diseases that attack the brain. But you can greatly reduce your risk for Alzheimer's if you can eat healthily and keep your weight under control," he concluded.
The study was funded by the National Institute on Aging, the National Institute of Biomedical Imaging and Bioengineering, the National Center for Research Resources, and the American Heart Association.
