"Having fat friends makes you fat, researchers from Harvard Medical School and the University of California says after after examining 12,067 individuals and 38,611 of their relatives and friends. In same-sex friendships, people were 71 per cent more likely to put on weight if a friend of theirs became obese. "It's not that obese or non-obese people simply find other similar people to hang out with. Rather, there is a direct, causal relationship," says Harvard professor Nicholas Christakis."