| "CHICAGO - Your friends may be more important than your genes in determining whether you gain weight, according to a "classic" study released Wednesday." " The study, which followed a large group of Americans for more than three decades, was the first to demonstrate that obesity -- and perhaps other health problems that involve behavior or lifestyle -- spreads through social networks." " A person's chances of becoming obese were found to increase by 57 percent if someone he considers a friend becomes obese, 40 percent if he has a sibling who becomes obese and 37 percent if his spouse becomes obese." " Immediate neighbors who aren't friends were found to have no effect on obesity, which lends support to the notion that one person is influencing the behavior of the other, rather than that both share a common exposure, such as socioeconomic class or lack of stores selling healthy food." " The researchers also controlled for the possibility that overweight people simply prefer to associate with others who are overweight or, as one of the authors, Dr. Nicholas Christakis, put it: "birds of a feather flock together."" " They excluded friends who were both overweight at the beginning of the study and looked only at people who became obese over time." " The research was not designed to explain why obesity spreads through social networks. But Christakis, of Harvard Medical School, said the most likely explanation is that "it's about the spread of norms from people to people. People change their minds about what constitutes an acceptable body-mass index" as their close friends gain or lose weight." " The stronger the friendship, the tighter the link: When two people each name the other as a close friend, and one of the two becomes obese, the chance for the other to follow suit goes up 171 percent." " An editorial accompanying the publication pointed out that the effect of social norms apparently can be greater than that of heredity: The risk of obesity increases by 30 percent in people who carry a single copy of a mutation in the FTO gene, known as the "fat gene," and by 67 percent in people who carry two copies." " In reaching their conclusions, researchers analyzed medical records of 12,067 people in the Framingham Heart Study, which has been following the health
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