How Obesity Really Is Like An Epidemic

"Obesity epidemic" is a cliche -- but it now appears that you can 'catch' weight gain from your friends.

Last weekend's New York Times magazine ran a fascinating article on recent research showing the power social networks have on physical and mental health. Your friends, it seems, influence your weight and even your happiness.

Clive Thompson writes about recent research conducted by Nicholas Christakis and James Fowler:

By analyzing the Framingham data, Christakis and Fowler say, they have for the first time found some solid basis for a potentially powerful theory in epidemiology: that good behaviors — like quitting smoking or staying slender or being happy — pass from friend to friend almost as if they were contagious viruses. The Framingham participants, the data suggested, influenced one another’s health just by socializing. And the same was true of bad behaviors — clusters of friends appeared to “infect” each other with obesity, unhappiness and smoking. Staying healthy isn’t just a matter of your genes and your diet, it seems. Good health is also a product, in part, of your sheer proximity to other healthy people.

Christakis and Fowler looked at participants in the long term Framingham (Mass.) heart study, which also recorded the names of participant's family and friends going back decades.

... they had a map of how 5,124 subjects were connected, tracing a web of 53,228 ties between friends and family and work colleagues. Next they analyzed the data, beginning with tracking patterns of how and when Framingham residents became obese. Soon they had created an animated diagram of the entire social network, with each resident represented on their computer screens as a dot that grew bigger or smaller as he or she gained or lost weight over 32 years, from 1971 to 2003. When they ran the animation, they could see that obesity broke out in clusters. People weren’t just getting fatter randomly. Groups of people would become obese together, while other groupings would remain slender or even lose weight.

(You can see the animation here -- click on "View Animation.")

The researchers found that if someone became obese, their friends were nearly 60% likely to also become obese, and friend of friends 20% more likely.

Smoking follows a similar pattern, with different percentages, which makes sense to anyone who was ever in junior high.

The researchers and others suspect that these effects are the result of individuals adjusting behavior to the norms of their social groups.

The article is full of interesting spinoff findings, such as the way spouses don't influence each other, whether the number or quality of social connections is more important, and how even happiness (and unhappiness) spread like a contagion.

--- Here is the original "The Spread of Obesity in a Large Social Network over 32 Years" published in the New England Journal of Medicine.