For some people, fat in the belly makes the body less able to use insulin, which can lead to type 2 diabetes.

But researchers at the Joslin Diabetes Center said that some body fat may actually reduce insulin resistance.

Fat under the skin at the hips and thighs -- subcutaenous fat, as opposed to abdominal fat -- showed signs of this characteristic, said Dr. C. Ronald Kahn.

"This points to a new opportunity to find substances made by subcutaneous fat that may actually be good for glucose metabolism," he said. "If we can identify how subcutaneous fat does this, we will have a big clue as to where to look for these substances."

Kahn said the classic beer belly or apple shape, however, increases the risk of diabetes and mortality.

By transplanting fat into mice, the team was able to determine that the type of fat, not where it is on the body, creates the effect, however.

Earlier studies in humans had shown that removal of subcutaneous fat by liposuction does not result in improvement of any aspect of metabolic syndrome, a collection of medical problems related to insulin resistance, but none had focused on possible good effects of this subcutaneous fat.

However, one human study did show that obese individuals with high levels of both abdominal and subcutaneous fat were more insulin sensitive than those with only high levels of abdominal fat.