'Billy Bunter gene' makes children fat, say scientists

But scientists say that a propensity to look like Billy Bunter is mainly in the genes, with lifestyle playing a more minor role.

The study of more than 5,000 pairs of twins aged eight to 11 showed that genetics explained more than three quarters of the variation in weight among the youngsters.

In contrast, their home life accounted for just 23 per cent, the American Journal of Clinical Nutrition reports.

Researchers looked at identical pairs of twins, who share all their genes, and compared their measurements with non-identical pairs of twins, who only share half their genes.

Because pairs of twins are likely to have similar eating and exercise patterns to each other, it is a good way of comparing the role of nature and nurture in any weight gain.

Researcher Professor Jane Wardle said: "Contrary to the widespread assumption that family environment is the key factor in determining weight gain, we found this was not the case.

"This study shows that it is wrong to place all the blame for a child's excessive weight gain on the parents' behaviour; it is more likely to be due to the child's genetic susceptibility."

The finding comes as the UK faces soaring obesity rates. Child obesity has trebled in the last 20 years, with 10 per cent of six year olds and 17 per cent of 15 year olds now obese.

Adult obesity rates have nearly quadrupled over the last 25 years, making Britain the second-fattest nation in the developed world, behind the U.S.

Although overeating and a sedentary lifestyle are responsible for weight gain, the scientists said their research showed genetics was more important.

Professor Wardle, director of the charity Cancer Research UK's health behaviour research centre, stressed, however, that it is not inevitable that children with "obesity genes" become overweight.

"In today's environment, which provides unprecedented opportunities for all children to overeat and be sedentary, it is not surprising these tendencies result in weight gain," she said.

"It is therefore important to provide the best possible environment for all children to help protect those who are at higher genetic risk."