Japanese researchers have discovered a hormone in abdominal fat that has some of the same characteristics as insulin. The finding may mean that fat actually has dueling roles in regulating metabolism.
The authors of the study compared human fat from the abdominal area with fat from under the skin and found that the hormone, named visfatin, was more plentiful in the abdominal area.
Mouse studies had shown that visfatin behaves somewhat like insulin, although its effect is less powerful, perhaps because it tends to be present in much smaller concentrations. Insulin is the hormone responsible for ushering glucose, or blood sugar, out of the bloodstream. Lack of insulin or the inability of the body's cells to respond to it contributes to the development of diabetes.
When visfatin was administered to mice in high doses in earlier studies, it lowered blood sugar levels. Unlike insulin, however, visfatin levels do not change depending on whether a person is eating or fasting.
"The fact that fat secretes hormones has been increasingly obvious over the last several years," says Dr. Robert Rizza, president of the American Diabetes Association and professor of medicine at the Mayo Clinic College of Medicine in Rochester, Minnesota. A growing body of literature, including this new study, demonstrates it. Although this research is preliminary, it may one day hold the key to the treatment of diabetes, an increasingly common disease throughout the world. Rizza adds, "Fat all over the body is secreting a whole variety of different hormones that no one ever dreamed of."
The finding initially seems counterintuitive, because more fat in the mid-section—unlike fat under the skin is linked to an increased risk of diabetes as well as other health problems.
"We're finding more and more that fat can be thought of as a hormone-producing organ, and there are both good fat hormones and bad fat hormones," says Dr. Stuart Weiss, clinical assistant professor of medicine at New York University School of Medicine. "Fat hormones let the fat communicate with the rest of the body."
Neither Rizza nor Weiss was involved in the new study Dr. lichiro Shimomura of Osaka University, the study's senior author, explains that high levels of visfatin may contribute to "insulin resistance by continuously stimulating insulin receptors.
"Alternatively, as visfatin activates insulin receptors in a different manner from insulin, visfatin may be useful to treat insulin resistance in people," Shimomura says. One result of continuous insulin resistance is weight gain.
Experts Urge Caution
Despite the study's findings, many questions remain about visfatin. "This is a fascinating observation, but it requires considerable additional study," Shimomura says.
Weiss agrees. "We don't know the mechanism about how this hormone is controlled, and if it's higher or lower in different states of abdominal 'fatness.’ Either we need more of visfatin or less of it, depending on the metabolic consequences of high and low levels of the compound. It needs to be characterized and we need to know who has a lot and who has less and what the metabolic consequences are of high levels and low levels," Weiss says.