“Catching” obesity from friends and family….

Most of the researchers who are trying to make sense out of our obesity epidemic are focusing on genetic and physical variables. Consequently, it was interesting to read about a new study that suggests that our social networks influence our weight.

In an analysis of 32 years of data for over 12,000 adults, Nicholas Christakis of Harvard Medical School and James Fowler of UC San Diego found that people’s social networks affect their weight [1]. If you have a friend who becomes obese, your own chances of becoming obese go up 57 percent. An obese spouse raises your odds of becoming obese by 37 percent. Here is a nifty map of some of the results:

“A social network map of 2,200 people, the largest group of connected individuals in the Framingham Heart Study, in the year 2000.Each circle represents one person, and the size of each circle is proportional to that person’s body-mass index (BMI). Yellow circles indicate people who are considered medically obese and green circles indicate people who are not obese. Lines indicate family and friendship ties.”
Figure courtesy of James Fowler, UC San Diego.

My first reaction to this result was to think “birds of a feather flock together.” Not so, say Christakis and Fowler. Instead, they suggest that social contacts influence our norms about how big you can be. If your friends and family become obese, then you’re more likely to think that it’s okay to be obese yourself. The social norm hypothesis is also strengthened by data showing that social influence is stronger within one sex (hence the larger effects of having an obese friend rather than a spouse).

This makes a lot of sense to me. I’ve noticed that as more Americans get larger, it is becoming more acceptable to be large. There used to be a point where you wouldn’t try to wear certain clothing styles unless you had a fabulous figure, but those norms no longer seem to hold. 

If obesity is somewhat “contagious,” the good news is that the reverse could also be true. If one person loses weight, others around him or her will want to lose weight, too. We have noticed this effect in our own Jenny Craig saga. When people you know see you losing weight, they definitely want to know how you’re doing it. As Roger, Karen, and I became thinner, our neighbors on both sides signed up with Jenny, as did our daughter in Hawaii.

On a more random note, another funny observation about losing weight at my age is that people immediately assume you’re sick. I’ve had to reassure a large number of people that I am not suffering from a life-threatening condition–I’m just dieting.

1. Christakis, N., & Fowler, J. (2007). The spread of obesity in a large social network over 32 years. New England Journal of Medicine, 357, 370-379.