In the current online edition of the journal Human Brain Mapping, Paul Thompson, senior author and a UCLA professor of neurology, and lead author Cyrus A. Raji, a medical student at the University of Pittsburgh School of Medicine, and colleagues compared the brains of people who were obese, overweight, and of normal weight, to see if they had differences in brain structure; that is, did their brains look equally healthy.They found that obese people had 8 percent less brain tissue than people with normal weight, while overweight people had 4 percent less tissue. According to Thompson, who is also a member of UCLA’s Laboratory of Neuro Imaging, this is the first time anyone has established a link between being overweight and having what he describes as “severe brain degeneration.” “That’s a big loss of tissue and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer’s and other diseases that attack the brain,” said Thompson. “But you can greatly reduce your risk for Alzheimer’s, if you can eat healthily and keep your weight under control.” The researchers used brain images from an earlier study called the Cardiovascular Health Study Cognition Study. Scans were selected of 94 elderly people in their 70s who were healthy not cognitively impaired – five years after the scan was taken. To define the weight categories, they used the Body Mass Index (BMI), the most widely used measurement for obesity. Normal weight people were defined as having a BMI between 18.5-25; overweight people between 25-30, and obese people greater than 30. The researchers then converted the scans into detailed three-dimensional images using tensor-based morphometry, a neuroimaging method that offers high resolution mapping of anatomical differences in the brain.