Americans who struggle with their weight have a new excuse for their physical condition, and new hope that teamwork can turn things around.

A study released this summer in the New England Journal of Medicine shows that obesity tends to spread through families and friends, even when geographical distance separates them. According to the study, obesity doesn't necessarily spread through a person's social network because they share the same appetite. Instead, the close relationships appear to influence a person's perception of appropriate eating habits and acceptable weight.

'Weight is a complex issue, and social networks can work both for you and against you,' explains Dee Sandquist, director of Southwest's Center for Weight Management and national spokesperson for the American Dietetic Association. 'People need to look at this as a way to help identify the pitfalls in our lifestyles and work together to avoid them.'

The relationship factor makes a difference in obesity rates, according to the study. Siblings of obese participants in the study had a 40% increased chance of becoming obese themselves. A spouse's risk spiked by 37%, while friends of the same gender had an even higher risk of becoming obese-71%. The social network can also have a positive influence, the study showed, with evidence that good health and fitness is contagious, too.

'Social peer pressure can be very healthy when it comes to holding people accountable for the choices they make,' says Sandquist. 'In the office or at home, make the conscious decision to share healthy snacks and get a workout buddy to bring exercise into the equation. But also realize that it truly comes down to individual accountability to make lasting changes in your life.'