Body fat found under the skin - and particularly on the buttocks - may help reduce the risk of developing type 2 diabetes, research suggests.
The study contrasts this subcutaneous fat with visceral fat, which is wrapped around the organs, and raises the risk of ill health.
It is thought subcutaneous fat may produce hormones known as adipokines which boost the metabolism.
The Harvard Medical School study appears in the journal Cell Metabolism.
The researchers, who worked on mice, transplanted fat from one part of the animals' body to the other.
When subcutaneous fat was moved to the abdominal area, there was a decrease in body weight, fat mass, and blood sugar levels.
The animals also became more responsive to the hormone insulin, which controls the way the body uses sugar. A lack of response to insulin is often the first stage on the path to type 2 diabetes.
In contrast, moving abdominal visceral fat to other parts of the body had no effect.
Lead researcher Professor Ronald Khan said: "The surprising thing was that it wasn't where the fat was located, it was the kind of fat that was the most important variable.
"Even more surprising, it wasn't that abdominal fat was exerting negative effects, but that subcutaneous fat was producing a good effect."
Previous research has suggested that obese people with high levels of both abdominal and subcutaneous fat are more insulin-sensitive than those with only high levels of abdominal fat.
Professor Khan said it was possible that subcutaneous fat offset the effects of visceral fat.
Dr David Haslam, of the National Obesity Forum, said the finding cast new doubt on the merits of Body Mass Index (BMI) as a way to assess whether somebody was unhealthily overweight, as it did not differentiate between different types of fat.
He said it was still important that people tried to control their weight, as healthy lifestyle choices like a balanced diet and taking exercise would overwhelmingly impact on visceral, and not subcutaneous fat levels.
Women have a tendency to lay down more subcutaneous fat, particularly on their legs and buttocks than men.
Dr Ian Campbell, medical director of the charity Weight Concern, said: "If there is something about subcutaneous fat which is protective, and actually decreases insulin resistance, this could help open up a whole new debate on the precise role fat has on our metabolism."