Washington, July 20 - Overweight youth are twice as likely to gravitate towards obese peers for friendship, says a new study.

'Although this link between obesity and social networks was expected, it was surprising how strong the peer effect is and how early in life it starts,' said study co-author Thomas Valente.

Valente is professor in preventive medicine at the Keck School of Medicine, University of Southern California (USC).

Previous data had shown a connection between overweight adults and their social peers. However, the USC study used more advanced statistical modelling techniques than previous research and the association remained strong, Valente said.

'The findings certainly raise health concerns because when kids start associating only with others who have a similar weight status it can reinforce the negative behaviours that cause obesity,' he said.

In-school surveys were conducted among 617 students ages 11-13 from the greater Los Angeles area.