Gaining Weight as Friends, and Maybe Losing It Too(2/2)

Nicholas Christakis of Harvard Medical School was a lead investigator in the study. He says there is a direct causalrelationship between a person getting fat and being followed in weight gain by a friend.

The study found that the sex of the friends was also an influence. In same-sex friendships, a person had a 71% increased risk of becoming obese. Men had a 44% increased risk of becoming obese after weight gain in a brother. In sisters, it was 67%.

The researchers also considered the effect of where people lived in relation to each other. James Fowler of the University of California, San Diego, was the other lead investigator. He says a friend who lives a few hundred kilometers away has as much influence as one in the same neighborhood. He says the study demonstrates the need to consider that a major part of people's health is tied to their social connections.

Both investigators say their research shows that obesity is not just a private medical issue, but a public health problem.