Are your friends making you fat? Or keeping you slender? The short answer on both counts seems to be “yes.”
Research coauthored by UC San Diego’s James Fowler suggests that obesity and thinness are “socially contagious,” spreading from person to person in a social network.
The study, the first to examine this phenomenon, was published in the New England Journal of Medicine, and the findings were reported around the globe, including on the front pages of USA Today and The New York Times.
According to the study, if a person you consider a friend becomes obese, 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, however,
if one becomes obese, the likelihood of
the other becoming obese increases 40 percent; among spouses, 37 percent. There was no effect among neighbors.
Fowler and Harvard’s Nicholas Christakis analyzed data over a period of 32 years for 12,067 adults who were part of the Framingham Heart Study. Among the first things they noticed was that,
consistent with studies documenting an obesity epidemic in the U.S., the whole network grew heavier over time.
Also immediately apparent were distinct clusters of thin and heavy individuals. Statistical analysis revealed that this
clustering could not be attributed solely
to the selective formation of ties among people of comparable weights.
“
It’s not that obese or non-obese people simply find other similar people to hang out with,” says Christakis, a physician and a professor at Harvard Medical School. “Rather, there is a direct, causal relationship.” And the striking impact of friends seems to be independent of whether or not the friends live in the same region.
A friend 500 miles away has as much
effect as one next door, says Fowler, an
associate professor of political science at UCSD and an expert in social networks.
The researchers believe that people affect not only each other ’s behaviors, but also, more subtly, each other’s norms—each other’s ideas about what is an appropriate weight.
“There’s been an intensive effort to find genes that are responsible for obesity and physical processes that are responsible for obesity, and what our paper suggests is that you really should spend time looking at the social side of life as well,” says Fowler. “Social effects, I think, are
much stronger than people
” — Inga Kiderra |
