A gene variant present on chromosome 16 increases risk of obesity by 67 percent, researchers from the University of Oxford and the Peninsula Medical Center in Exeter report. Two variations in this gene called FTO accounted for an extra 7 pounds in people carrying them as compared to people having a normal gene.

People who had one variation of the FTO gene had a 30 percent higher risk of obesity and carried over 2 pounds extra weight than their normal counterparts.

The details of the report are available in the online edition of the journal Science.

The FTO gene was initially discovered when scientists were hunting for links between type 2 diabetes and obesity. That study involving 2,000 diabetics threw light on the variations in FTO gene. A second study involving 38,759 white Europeans confirmed the association of FTO variant and body mass index (BMI).

The presence of the gene variant may explain why some people eat plenty of food, but do not gain weight, while others eat scantily, but put on the pounds.

"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?'" said lead researcher Andrew Hattersley, D.M., of the Peninsula Medical School.. "There is clearly a component to obesity that is genetic."

Researchers said the present study was the best genetic link to obesity as a common variant was found. Previous genetic links were rare and not found commonly among obese people, they said.

The World Health Organization has declared obesity as a global epidemic having major health implications in 1997. It estimated that some 2 billion people worldwide are obese or overweight. Last year a report in the Journal of American Medical Association revealed increasing obesity and overweight rates among Americans.

Based on National Health and Nutrition Examination Survey (NHANES), conducted during 2003-2004, the report found 33.6 percent of children and adolescents were overweight in 2003-04, while 32 percent adults were obese.

While the above study suggests there is more to obesity than just overeating, the best way to combat it remains changing the lifestyle and getting plenty of exercise.