Narrator:       This is Science Today. If you have friends who are obese within your social network -- even those hundreds of miles away -- you have a much greater chance of becoming overweight yourself. Those were the findings of a novel study co-authored by James Fowler, an expert in social networks at the University of California, San Diego. But wait -- thinness is contagious, too!

Fowler:           And so really, whenever you're trying to make your life better, you should try to do it in groups rather than on your own, because that's really what's going to help you achieve your own health goals.

Narrator:       The Harvard-UC San Diego study also found the phenomenon of one person's weight affecting another's extends out three degrees of separation.

Fowler:           It affects my friend's friends, it also affects my friend's friend's friends. So this extends really to a large group of people. So, when we help one person lose weight, we're not just helping one person - we're helping many and that needs to be taken into account by policy analysts and also by politicians who are also trying to decide what the best measures are for making society healthier.

Narrator:       For Science Today, I'm Larissa Branin.