Proof: There IS a gene that makes you fat

They say the genetic make-up of one in six Britons increases their risk of becoming dangerously overweight by 70 per cent and their chance of developing diabetes by a half.

The study, led by geneticists from Oxford University and the Peninsula Medical School in Exeter, could lead to ways of treating and even preventing the condition that blights the health of millions.

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It could pave the way for tests for people to find out if they carried the gene. One day, couples could even choose to have babies free of fat' genes.

The findings may also help explain why some people find it harder to lose weight than others.

The researchers spent 15 years analysing the DNA and health of more than 40,000 adults and children before pinpointing a gene called FTO, which is common in the UK.

Professor Graham Hitman, of Queen Mary's School of Medicine in London, said: "We live in a blame culture, in which, when people gain weight, it is entirely their fault.

"This exciting research confirms that while improving lifestyle is still the key, some people will find it harder to change their weight than others."

Britain has the worst weight problem in Europe, with almost a quarter of adults classed as obese and obesity figures among children more than doubling in ten years.

Experts have warned that an entire generation faces an old age blighted by heart disease, cancer, diabetes and other diseases brought on by obesity.

The research, funded by the Wellcome Trust and reported in the journal Science, pinpointed a flawed version of the FTO gene. It is the first time a specific gene has been linked to obesity.

As genes come in pairs, the people at greatest risk are those who carry two flawed versions of FTO. They are around half a stone heavier than average.

Those who have inherited just one flawed gene are 30 per cent more likely to be obese and 25 per cent more likely to develop diabetes than those who have two normal copies.

The scientists said the flawed gene affects the weight of both adults and children, with its influence kicking in by the age of seven. They do not know yet how it affects the body, however.

Exeter researcher Professor Mark Hattersley said: "As a nation, we are eating more but doing less exercise, and so the average weight is Continued from Page One increasing. But within the population some people seem to put on more weight than others.

"Our findings suggest a possible answer to someone who might ask 'I eat the same and do as much exercise as my friend next door, so why am I fatter?' There is clearly a component to obesity that is genetic." Professor Mark McCarthy, from Oxford, said it was likely FTO is just one of several genes linked to obesity.

Urging people not to get the idea that losing weight is out of their control, he said: "Being overweight is probably a combination of genes and other factors and people still have control over these other factors and are still able to lose weight.

"Many people have this variant but are not overweight."

He added: "The work we are going to do down the line might translate into new ways of treating or preventing obesity. That is the chink of light these discoveries translate."

Treatment could be tailored around drugs shown to work best on a particular genetic make-up.

It is already possible to buy genetic tests which claim to be able to predict other conditions such as heart disease.

Their use is controversial, however. While some people may use the information to alter their lifestyle to stay as healthy as possible, others may take a fatalistic approach and simply let nature take its course.

The obesity researchers have also warned that there are other, as yet undiscovered, genes involved in obesity, casting doubt on the usefulness of a test aimed at FTO alone.

Leading nutritionist Dr Susan Jebb, of the Medical Research Council's Human Nutrition Research centre in Cambridge, said: "People who know they are carriers may be more motivated to adopt a prudent diet and healthy lifestyle to decrease their risk.

"Obesity is a complex disorder and there is no evidence from this research to suggest that carriers of the gene will not successfully lose weight by decreasing their energy intake and becoming more active."

The research comes in the wake of the world's largest study of weight loss, which showed that diets do not work for the vast majority of slimmers - and may even put lives at risk.