A new study from University of California in Los Angeles suggests that piling on the pounds can shrink brains of older people, making them more vulnerable to cognitive problems.
According to Paul Thompson, brains of elderly obese people looked 16 years older than the brains of leaner peers.
The research involving 94 people in their 70s showed that people with higher body mass indexes had smaller brains on average, with the frontal and temporal lobes - important for planning and memory, respectively - particularly affected.
While no one knows whether these people are more likely to develop dementia, a smaller brain is indicative of destructive processes that can develop into dementia.
The team also found that the brains of the 51 overweight people were 6 per cent smaller than those of their normal-weight counterparts, on average, and those of the 14 obese people were 8 per cent smaller.
"The brains of overweight people looked eight years older than the brains of those who were lean, and 16 years older in obese people," New Scientist quoted Thompson as saying.
Thompson suggests that as increased body fat ups the chances of having clogged arteries, which can reduce blood and oxygen flow to brain cells, the resulting reduction in metabolism could cause brain cell death and the shrinking seen.
He said that exercise protects the very brain regions that had shrunk.
"The most strenuous kind of exercise can save about the same amount of brain tissue that is lost in the obese," he said.
The findings appear in journal Human Brain Mapping.