A study by American scientists, published today, offers evidence supporting the theory that fat is infectious and is caused by a family of viruses that affect certain people.

Although lack of exercise and poor diet remain the most obvious contributors to obesity, some scientists believe that these do not explain why it has become so commonplace. However, other scientists have questioned the research, in which only 15 obese and five non-obese people were tested.

Obesity rates in the UK have almost doubled in adults in the past decade, and tripled in children in the past 20 years. On present trends, half of all children in England in 2020 will be obese, with many expected to die before their parents as a result of diabetes and other obesity-related diseases.

Research by a team from the University of Wisconsin has identified a virus called Ad-37 — one of 50 adenoviruses found in humans — which causes obesity in chickens. Two related human adenoviruses, Ad-36 and Ad-5, have also been shown to cause obesity in animals. The finding have raised the prospect of research into a vaccine.

An earlier study involving screening of people for Ad-36 found significantly higher levels of the virus among obese people, with one in six testing positive, compared with none in a non-obese group.

The latest study, reported in the American Journal of Physiology, suggests that Ad-37 also may be implicated in human obesity. Leah Whigham, the lead researcher, said that more work was needed before a vaccine could be found. “The nearly simultaneous increase in the prevalence of obesity in most countries of the world is difficult to explain by changes in food intake and exercise alone,” the study noted.

Dr Whigham said: “The etiological factors producing this epidemic have not been clearly identified. It makes people feel more comfortable to think that obesity stems from lack of control. It’s a big mental leap to think you can catch obesity.”

She said that people should eat sensibly and exercise, but also wash their hands to prevent infection.

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