Scientists believe they have identified the human gene that acts as an obesity "master switch" and controls the process of depositing fatty tissue under the skin.

The researchers have also demonstrated that it is possible to turn the genetic switch off using substances that one day maybecome the basis of a new generation of diet pills.

The discovery – one of many coming from the fast-paced research that is continuing into gene structures and DNA – could be a breakthrough in medical treatment for clinical obesity.

Two independent teams of scientists from Harvard University and the drug company Pfizer discovered after studying mice that the PPARgamma gene is critical for making fat.

The formation of fatty tissue, called adipogenesis, is a two-step process involving the conversion of an undifferentiated type of skin cell, called a mesenchymal cell, into a fully formed fat cell.

Bruce Spiegelman, from Harvard, and Heidi Camp, from Pfizer, found that the PPARgamma gene controls the second stage of development, when a pre-fat cell fills with lipids to become the mature adipocyte, or fat cell.

Removal of the gene from mouse cells completely arrested the process of fat development, showing PPARgamma is the critical component in the formation of fat, the scientists said.

When the researchers blocked the action of the PPARgamma gene with specific chemical inhibitors that bind to DNA, called zinc finger proteins, fat development was also stopped dead.

Dr Camp went on to show that just one of the two protein products of the gene, called PPARgamma2, is solely responsible for fat formation.

The research has been published in the scientific journal Genes & Development.

A spokesman for Harvard said: "The determination that PPARgamma2 is necessary for fat cell development provides a target for rational drug design in the battle against the bulge."

Earlier research had implicated the same gene in a range of other disorders, such as heart disease, diabetes and cancer. Finding a method of blocking its function may help in the development of new treatments for these conditions.

Obesity is one of the fastest growing medical disorders in the western world, with about one in four adult Americans and nearly one in five Britons suffering from serious, health-affecting weight problems.