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Pounds in the right place.
A new study in mice finds that subcutaneous fat, which in people builds up in the hips and legs, can have benefits.

Credit: Jim Naughten/Corbis

Extra Pounds a Boon?

By Jennifer Couzin
ScienceNOW Daily News
6 May 2008

For most overweight people, excess fat sits in one of two areas: deep inside the abdomen (visceral fat) or around the hips and legs (subcutaneous fat). Researchers have recognized for some time that visceral fat is the greater evil. People with lots of it are much more prone to diabetes, heart disease, and other problems than people with excess subcutaneous fat. But it's not clear exactly why. Is the fat itself different, or does its location in the body matter?

To probe this question, C. Ronald Kahn, director of obesity research at the Joslin Diabetes Center in Boston, and his colleagues devised a relatively simple experiment. They transplanted fat in 42 naturally plump, healthy mice. The mice were divided into four groups that underwent different types of operations. In some, the researchers added visceral or subcutaneous fat to the abdomen. In others, they tucked visceral fat or subcutaneous fat under the animals' flanks, the rough equivalent to the hips. Thirteen other animals formed a control group; they were operated on but didn't receive extra fat.

Kahn's team found some surprising benefits to subcutaneous fat. Mice with subcutaneous fat transplanted into their abdomen gained only about 60% of the weight packed on by the control group, which, like most mice, continued to expand. These transplant recipients also had better glucose and insulin levels. The mice that got extra subcutaneous fat in subcutaneous areas also fared better than controls, although not as well as the first group. Those that had visceral fat added to their visceral cavity were the worst off, the group reports today in Cell Metabolism. Autopsies on the mice confirmed that the transplanted fat was still in place.

The finding suggests that subcutaneous fat can benefit health, says Kahn. "That's the surprise twist in the story."

The implications are "that subcutaneous fat produces something that's good for you, and that visceral fat produces something that's bad for you," says Richard Bergman, a diabetes and obesity researcher at the University of Southern California in Los Angeles. Although some studies have correlated excess subcutaneous fat in people with improved insulin levels, the new work is "the most comprehensive study to date" examining this, says Philipp Scherer, a diabetes and obesity researcher at the University of Texas Southwestern Medical Center in Dallas.

But for Bergman, the finding is so unexpected that he's keen to see more evidence, in particular a clue to the "magic factor" that might explain the health benefit. "Putting subcutaneous fat in the visceral compartment is something that never happens naturally, so it's hard to interpret," he says.