Wednesday, July 25, 2007

Study Says Obesity Can Be Contagious

New York Times: By GINA KOLATA

Obesity can spread from person to person, much like a virus, researchers are reporting today. When a person gains weight, close friends tend to gain weight, too.

Their study, published in the New England Journal of Medicine, involved a detailed analysis of a large social network of 12,067 people who had been closely followed for 32 years, from 1971 until 2003. The investigators knew who was friends with whom, as well as who was a spouse or sibling or neighbor, and they knew how much each person weighed at various times over three decades. That let them examine what happened over the years as some individuals became obese. Did their friends also become obese? Did family members or neighbors?...

Dr. Nicholas Christakis, a physician and professor of medical sociology at Harvard Medical School and a principal investigator in the new study, says one explanation is that friends affect each others’ perception of fatness. When a close friend becomes obese, obesity may not look so bad.

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

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 some friends with them....

The effects, Dr. Christakis said, “highlight the importance of a spreading process, a kind of social contagion, that spreads through the network.”

Of course, the investigators say, social networks are not the only factors that affect body weight. There is a strong genetic component at work as well. ...

It also may mean that the way to avoid becoming fat is to avoid having fat friends.

That is not the message they meant to convey, say the study investigators, Dr. Christakis and his colleague, James Fowler, an associate professor of political science at the University of California in San Diego.

You don’t want to lose a friend who becomes obese, Dr. Christakis said. Friends are good for your overall health, he explains. So why not make friends with a thin person, he suggests, and let the thin person’s behavior influence you and your obese friend?

That answer does not satisfy obesity researchers like Kelly Brownell, director of the Rudd Center for Food Policy and Obesity at Yale University.

“I think there’s a great risk here in blaming obese people even more for things that are caused by a terrible environment,” Dr. Brownell said. ...

Does this finding carry over to students? Should informed consent be mandated when students attempt to register?

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