| "A new 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." ", found that a person's chances of becoming obese went up 57 percent if a friend became obese, 40 percent if a sibling did and 37 percent if a spouse did." "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 other's chance of following suit goes up 171 percent." "The same effect seemed to occur for weight loss. But most of the people studied gained weight." "The researchers think it's more than just people with similar eating and exercise habits hanging out together. Instead, it may be that having relatives and friends who become obese changes one's idea of acceptable weight." "People of the same sex influenced each other the most. In same-sex friendships, an individual was 71 percent more likely to become obese if a friend did. But friends and siblings of opposite genders had no increased risk." ""People are more likely to copy the actions of people they resemble," said co-author Nicholas Christakis of Harvard Medical School. "What we think is going on here is emulation."" "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 healthful food." ""We were stunned to find that friends who are hundreds of miles away have just as much impact on a person's weight status as friends who are right next door," said co-author James Fowler of the University of California, San Diego." "The researchers also controlled for the possibility that overweight people simply prefer to associate with others who are overweight or "birds of a feather flock together," as Dr. Christakis put it. They excluded friends who were both overweight at the beginning of the study and looked only at people who became obese over time." "The researchers analyzed medical records of people in the Framingham Heart Study, which has been following residents of Framingham, Mass., for more than 50 years. They tracked records for relatives and friends using contact information that participants provided each time they
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