Scientists spot the gene that trims fat

London: The mystery of how some people can eat and never put on weight while others struggle to shed an ounce may have been solved by scientists.

Slight differences in a single gene could be responsible for suppressing the metabolism, making carriers of one variation permanently sluggish and unable to burn calories as effectively as others. In contrast, those, thinner, people carrying the other version seem to use up energy more rapidly, expending it through excess heat.

Scientists have long suspected that genetic differences were responsible for weight gain and singled out one particular gene, known as the FTO gene, as the main suspect.

People with a high-risk version weigh on average 6lb 9oz more than those with a low-risk version. But experts could not understand how the variation made a difference, putting forward theories that it could influence appetite and food intake.

However, it now appears the gene may control the rate of metabolism. In experiments on mice, those entirely without the gene were found to remain lean.

The scientists, led by Dr Ulrich Ruther, from the University of Dusseldorf, in Germany, found the mice remained thin despite eating large amounts of food and being inactive.

The research, reported in Nature, suggested they were burning up energy faster than animals with a functioning version of the gene. It is thought that it may limit energy given off as heat.

Prof Stephen O'Rahilly, a metabolism expert from Cambridge University, in England, said: "Genetic variation close to the FTO gene is definitely associated with obesity in humans.

"But until now it was not clear whether this genetic variation was likely to influence obesity by altering the expression or function of the gene itself or some neighbouring gene. This work shows that if mice lack the FTO gene they are very lean because they spontaneously burn off enormous amounts of energy."