Obese people have 8 percent less brain tissue than those of normal weight, according to a study of cadaver brains by researchers from UCLA and the University of Pittsburgh.

The doctors said in a news release that those considered overweight had 4 percent less tissue than those with body-mass index scores in the normal range.

Paul Thompson of UCLA said it was the first study to show that being overweight is associated with 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," Thompson said.

In looking at both gray matter and white matter of the brain, the researchers said they found that the people defined as obese had lost brain tissue in the frontal and temporal lobes, areas of the brain critical for planning and memory, and in areas involved in attention, long-term memory and movement.

"The brains of obese people looked 16 years older than the brains of those who were lean, and in overweight people looked eight years older," said Thompson.

The results were published in the online edition of the journal Human Brain Mapping.