Irisin, a hormone secreted by muscle cells and identified by researchers at Harvard Medical School could be the key to the ultimate dream of obese people and weight watchers across the world. The study, published in the latest issue of the scientific journal Nature , could hold promise for the treatment of metabolic syndrome, a known risk factor for cardiovascular diseases and diabetes. Obesity is the most important symptom of metabolic syndrome.

Researchers from Dana-Farber Cancer Institute, Massachusetts, Harvard Medical School, University of California and Denmark's Odense University Hospital among others, have found that some of the most widely recognised effects of exercise on muscle are mediated by irisin, which is formed by the cleaving of the membrane protein FNDC5.

It is already known that a chemical called PGC1-alpha mediates the effects of exercise on muscles. The researchers found that PGC1-alpha raises levels of FNDC5 by stimulating its transcription.

"Irisin is induced with exercise in mice and humans, and mildly increased irisin levels in the blood cause an increase in energy expenditure in mice with no changes in movement or food intake. This results in improvements in obesity and glucose homeostasis. Irisin could be therapeutic for human metabolic disease and other disorders that are improved with exercise," says the study.

The hormone has been found to act in two ways. It promotes the conversion of inert yellow fat to the metabolically more active brown fat, and facilitates insulin action, thus decreasing blood glucose levels. The researchers found irisin to be present in the blood of human volunteers who had undergone ten weeks of exercise.

When irisin was introduced in sedentary mice, the physiological effects of exercise like higher metabolism, stabilisation of blood glucose levels through better uptake of glucose from blood -- one of the mechanisms by which insulin works -- were mimicked in the laboratory.

Dr Ambrish Mithal, chairman of endocrinology and diabetes at Medanta Medicity, said the research for the first time pinpoints a single chemical for the effects of exercise. "With the present body of knowledge it is not possible to explain all the effects of exercise in the body. Here they have identified a mediator that is capable of achieving all those effects without exercise. This is a very exciting discovery with a lot of therapeutic potential for problems like diabetes and obesity," Dr Mithal said.