Is fat catching? Scientists discover the cold virus that makes you obese

Scientists say obesity may be caused by a virus that causes colds and sore throats and is spread through dirty hands.

Their research could hasten the development of an anti-obesity vaccine.

The notion that being overweight is contagious may also help explain soaring rates of obesity - which raises the risk of diseases like heart disease and cancer.

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Adult obesity rates have nearly quadrupled in Britain over the last 25 years and some experts claim there must be more than diet and exercise at play.

One contender is the adenovirus - the bug behind up to ten per cent of colds and sore throats.

Spread by coughs, sneezes and dirty hands, the virus can also cause stomach upsets and conjunctivitis.

Previous studies have shown that chickens and mice infected with the virus put on weight more quickly than uninfected animals - even when they don't eat any more food.

Human studies show that almost a third of obese adults carry the virus compared to 11 per cent of lean men and women.

The latest research used samples of fatty tissue from those who had undergone liposuction.

Experts at Louisiana State University showed the virus could trigger the development of fat cells in the body.

When stem cells - master cells that can change into other cells and tissue - were infected with adenovirus they grew into fat cells.

Presenting her findings at the American Chemical Society's annual conference, Dr Magdalena Pasarica said: "We're not saying that a virus is the only cause of obesity, but this study provides stronger evidence that some obesity cases may involve viral infections.

"Not all infected people will develop obesity. We would ultimately like to identify the underlying factors that predispose some obese people to develop this virus and actually find a way to treat it."

The research could lead to the development of anti-adenovirus drugs or vaccines aimed at combating the obesity epidemic.

Experts said it was important to research the causes of obesity - but no one should underestimate the importance of diet and exercise.

Dr David Haslam, of the National Obesity Forum, said: "A vaccine won't help people from eating the food put in front of them at fancy restaurants - it isn't going to change people's lifestyle.

"Even if a tiny part of obesity is caused by a virus, the food you put in your mouth and the activity you don't do is key."

Almost a quarter of adults in Britain are obese, making us the second fattest nation in the developed world. The US is first.

Child obesity rates have trebled over the last 20 years - 10 per cent of six-year-olds and 17 per cent of 15-year-olds are obese.

By 2050 half of all primary school boys and a fifth of girls could be so overweight their health is at serious risk.