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Big by association

(article, Stephanie Beechem)

Gained a few pounds this year? A new study in the New England Journal of Medicine suggests that you might want to blame your friends. 

The study analyzed a social network of 12,067 people in Framingham, Massachusetts, all of whom had been followed for 32 years in a well-known federal study of heart disease. Obesity, the study's authors concluded, is like an epidemic, in that it can spread from person to person in close social networks. When you gain weight, chances are that a friend will, too. 

The co-authors of the study — Dr. Nicholas Christakis, a physician and professor at Harvard Medical School, and James Fowler, a professor of political science at the University of California San Diego — explained to the New York Times that their study was unique because it followed a social network rather than a single individual and his or her contacts. This allowed the study to determine which relationships posed the highest risk for mutual weight gain. 

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Friends had far more influence over weight gain than family members or spouses. If one person became obese, the study reported, a friend's chances of becoming obese as well went up by 57 percent. And if that friend was a close friend? The risk rose to 171 percent. 

So how does weight gain spread through a social network? Gina Kolata summed up one of the theories in the New York Times:

bq. One explanation was that friends affected each others’ perception of fatness. When a close friend becomes obese, obesity may not look so bad.

bq. “You change your idea of what is an acceptable body type by looking at the people around you,” Dr. Christakis said.

bq. The investigators say their findings can help explain why Americans have become fatter in recent years — each person who became obese was likely to drag along some friends.

The idea that obesity can spread from friend to friend worries many people, including researcher Kelly Brownell at the Rudd Center for Food Policy and Obesity at Yale. Will this study lead to further stigmatization of overweight people, for example? Will people will begin to network solely with thinner friends to avoid the risk of becoming overweight through social connections?

Kolata pointed out that as Americans began to shun smoking in large numbers, smokers themselves began to be shunned:

bq. The Framingham data from the 1970s show smokers embedded in social networks just like everyone else. But by the 1990s, smokers began to be shunted to the side, their links to nonsmokers breaking.

So will we become a nation of fat-lovers or fat-shunners? Check out the mesmerizing animation created by the study researchers, which illustrates just how obesity can spread throughout a complex social network. And take a look at Revolution Health's map of the U.S., which shows obesity rates by state since 1990.

Keep in mind, too, that a different New York Times_ article recently argued that fat has been given a disproportionately bad rap, when in fact it is one of our body's smartest ways to store excess calories. Fat balances our energy, helps regulate hormones and reproduction, and fuels our brains. Since fat is now closely associated with the words "epidemic" and "health crisis," those beneficial qualities are easy to forget.

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