Fat is Socially Contagious

Fat is Socially Contagious

A recent study found that if one person becomes obese, those closely connected to them have a greater chance of becoming obese themselves. Surprisingly, the greatest effect is seen not among people sharing the same genes or the same household but among friends. 

If a person you consider a friend becomes obese, the researchers found, your own chances of becoming obese go up 57 percent. Among mutual friends, the effect is even stronger, with chances increasing 171 percent. 

Among siblings, if one becomes obese, the likelihood for the other to become obese increases 40 percent; among spouses, 37 percent. There was no effect among neighbors, unless they were also friends. 

"It's not that obese or non-obese people simply find other similar people to hang out with," said Christakis, a physician and a professor in Harvard Medical School's department of health care policy. "Rather, there is a direct, causal relationship." 

Further analysis also suggested that people's influence on each other's obesity status could not be put down just to similarities in lifestyle and environment, to, for example, people eating the same foods together or engaging in the same physical activities. Not only do siblings and spouses have less influence than friends, but also geography doesn't play a role. The striking impact of friends seems to be independent of whether or not the friends live in the same region.

"When we looked at the effect of distance, we found that your friend who's 500 miles away has just as much impact on your obesity as [one] next door," said Fowler, an associate professor of political science at UC San Diego and an expert in social networks.

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