Fat people tend to have fat friends

CAMBRIDGE, Mass., March 9 (UPI) -- Having overweight friends and family increases the chances you'll be overweight as well, a Harvard researcher said.

Medical sociology professor Nicholas Christakis studied obesity and social network data from more than 5,000 people.

His study found "obesity clusters" with the highest chances of weight gain among those who mutually described each other as friends.

Same-sex friends had a greater effect on each other than different-sex friends.

"Men are much more influenced by weight gain in men and women influenced by weight gain in women," Christakis said. "Sibling effects exist, and weight gain in same-sex siblings are more important than those in different-sex siblings."

The study also found that social distance, not physical distance, is important. While obesity in friends and family has an effect, the study showed that there was no effect from weight gain by unrelated neighbors. Proximity to fast-food restaurants did not have any impact.

Christakis said he believes the results illustrate the changing norms -- the acceptability of gaining weight -- through social networks, rather than the spread of particular behaviors that have similar results.