Besides genes and an unhealthy diet, your friends can also play a role in making you overweight, says a study, which found that obesity can spread through communities like a 'social contagion'.

The study showed social circles can influence a person to become obese, suggesting the risk of becoming overweight increases if one moves to an area with a high rate of obesity, the Daily Mail reported.

"Social contagion in obesity means if more people around you are obese, then that may increase your own chances of becoming obese. Subconsciously, you are affected by what people around you are doing," said Ashlesha Datar at the University of Southern California.

"If you move to a community where a sedentary lifestyle is the norm, you join that. There is this social influence," Datar said.

For the study, the team included 1,314 parents and 1,111 children of US Army personnel at 38 bases.

The chances of becoming overweight or obese for a teenager increased four-six per cent for rise in every one per cent in the obesity.

On the other hand, the risk of the parent becoming obese or overweight went up five per cent for increase in every one per cent of obesity in the area.

The longer the families lived there, the more likely they put on weight, the report said.

Obesity can be caused by many variables, and previous research has shown living in certain communities carries a higher risk of obesity than living in other communities.

IANS