" People whose friends become obese have a greater chance of also getting too fat, a finding that suggests that obesity is "socially contagious," spreading from one person to another like a disease, according to a new study released Wednesday."

"Geographic distance between friends doesn't matter -- the influence of friendship is the same whether friends live next-door or 500 miles away, according to the report in the New England Journal of Medicine."

"The study, conducted by Dr. Nicolas Christakis of Harvard Medical School and James Fowler of the University of California, San Diego, was the first to document the spread of obesity through a social network -- a pattern of contagion most often associated with infectious diseases, such as influenza and AIDS."

""This is not birds-of-a-feather-flock-together. It's not that obese or non-obese people simply find other similar people to hang out with," Christakis said. "Rather, there is a direct causal relationship.""

"The report offers a nuanced understanding of the forces driving the steady rise in obesity during the last 25 years -- a trend that has been linked to cheap fast food, a sedentary lifestyle and genetic factors."

"The study suggests many of those factors have a role but their influence is amplified through social connections."

"The study analyzed social and family connections among 12,067 people from Framingham, Mass., who had been closely followed for 32 years, from 1971 until 2003, in the Framingham Heart Study. The study collected data on health, diet, exercise, family ties and, to a limited extent, friendships. Every two to four years, participants had a physical exam."

"Researchers looked closely at the influence of gender, smoking, socioeconomic class and geographic distance among participants."

"They used body mass index, a ratio of height to weight, to calculate obesity. A BMI of 30 or more is considered obese."

"Researchers found that the influence of friends on weight gain exceeded that of siblings and spouses, and was as powerful as the effect of genetics found in other studies."

"Neighbors who weren't friends had no influence on each other, suggesting community characteristics often linked to obesity -- such as a lack of parks or a dependence on cars -- weren't as important as thought."

"Researchers said the weight gains couldn't be attributed to smoking cessation, another explanation offered for the spread of obesity."

"Specifically, researchers found that if a person becomes obese, the chances that a friend will become obese rises 57 percent."

"Mutual friends -- study participants who identified each other as friends -- had the greatest influence. If one became obese, the risk skyrocketed 171 percent."

"In same-sex friendships, the chance that a friend will become obese increases 71 percent. Among brothers, the odds go up 44 percent. Among sisters, the risk jumps 67 percent."

"Friends and siblings of the opposite sex had no influence on weight
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