Fat can be turned into muscle at the flick of body switch

A genetic "switch" that determines whether body tissue turns to muscle or fat has been discovered by scientists hoping to develop an anti-obesity drug.

A genetic "switch" that determines whether body tissue turns to muscle or fat has been discovered by scientists hoping to develop an anti-obesity drug.

They have been able to convert pre-fat cells into muscle by simply turning the switch on. But when the switch was turned off, the cells continued to develop into mature fat tissue, showing it is possible to interfere with the metabolism that makes muscles flabby.

Ormond MacDougald, assistant professor of physiology at the University of Michigan in Ann Arbor, said the discovery could explain why some people remain slim yet others are persistently overweight. "The switch may play a role in determining the increasing flabbiness that comes with ageing or with the fat differences between men and women," he said.

"This is just the first piece of the puzzle, but it is an important one. Understanding this developmental pathway could help scientists to learn how and why obesity develops." The study, in the journal Science, focused on a protein called "wnt", produced by a gene involved in the development of immature cells.

When wnt is absent, the precursor cells of both muscle and fat develop into fat. Although the study was done on mouse cells, researchers believe it is applicable to humans who are thought to use the same fat-making mechanism.

Professor MacDougald said there is no evidence for a fully mature muscle cell being converted into fat, only for immature muscle cells being turned into fat cells with wnt.

"This protein is not a likely target for an anti-obesity drug," he added. "It seems to be involved in a number of other functions as well, so the potential side-effects are very real. Our goal is to create a fat-free mouse."