You are fat because your friends are fat. Get rid of them – or at least help them lose weight. Harvard scientists found that people are 57 percent more likely to be overweight if they have overweight friends.

The risk triples among close friends. Fat is contagious even when overweight friends live in another state. Geographical distance did not alter the relationship. Fat runs in families. The risk of gaining weight increased by 40 percent if a sibling was fat and by 37 percent if the spouse was pudgy.

The researchers speculated that hanging out with fatter people creates a higher tolerance for larger body sizes. The reverse was true: people weighed less when they had physically active or lean friends.

The study examined more than 12,000 people over 30 years of age. The 12,000 people formed obesity clusters – those with the greatest interaction with others in the group tended to be obese. The study showed that obesity is “contagious.” [sources: New England Journal of Medicine, Fitness RX]