Traci Watts in The National Geographic:
An expanding waistline may lead to a shriveled brain, new research suggests. In a long-term study of people in their early 60s, a brain region called the hippocampus shrank close to 2 percent a year in those who were obese—a rate approaching levels seen in Alzheimer's disease. In people of normal weight, the hippocampus, which is crucial for processing memories for later retrieval, shrank roughly half as much, according to an eight-year study discussed at a press conference Tuesday at the Society for Neuroscience meeting in Washington, D.C. Earlier research on weight and the brain focused mostly on the impacts of obesity in middle-aged people, said neuroscientist and study co-author Nicolas Cherbuin of the Australian National University, in Canberra. But participants in the new study were 60 to 64 years old when the study began, providing evidence of a link between elderly corpulence and declining cognitive powers—sobering news in nations such as the United States where the population is getting both older and fatter. “People may think, 'Oh, well, I'm in old age, I'm retired, it won't matter.' It does matter,” Cherbuin said. “The more obese one is, the more shrinkage there will be.”
Cherbuin and his colleagues used magnetic resonance imaging (MRI) to examine the brains of more than 400 people in their 60s who'd volunteered for a study of aging. At the beginning of the study, obese subjects already had smaller hippocampuses than did subjects who were merely overweight. (A person who stands five feet, nine inches tall is overweight at 169 to 202 pounds and obese at 203 pounds or more, according to the formula used by the U.S. Centers for Disease Control and Prevention.) That linkage between weight and hippocampus size held even when researchers took into account education, physical activity, and other factors that might have led to differences in hippocampal size. As if it weren't bad enough that they started out with smaller hippocampuses, the obese subjects lost hippocampal volume more quickly than their slimmer fellows did. The rate of hippocampal shrinkage seen in the fatter participants is likely to lead eventually to memory loss, mood changes, and problems with concentration and decision-making, Cherbuin said.