Something in the Air

Are People Catching Obesity from Friends and Neighbors?

It’s an uncomfortable notion sparking intense interest. Are people catching obesity from others in their social networks? A new study in JAMA Pediatrics lends further credibility to this idea. But the big question remains a puzzle. Exactly how does that work?

A Natural Experiment

Ashlesha Datar and Nancy Nicosia used data from the Military Teenagers’ Environments, Exercise, and Nutrition Study to probe this question. Random military assignments that moved families to different communities served as a way to overcome the influence of self-selection in prior studies. Datar and Nicosia looked at the BMI of teens and their parents assigned to different locations. Some of those locations were in counties with high rates of obesity. Some were much lower.

Their question was: did random assignment to a community with high obesity rates increase a person’s risk of obesity?

And indeed they found that it did. In fact, the longer they stayed in those communities, the higher their risk became.

Social Contagion and Built Environment

Of course, an obvious question follows. What brings the added risk in these communities? Is it the people in the community? Or is it the physical environment they share? Datar and Nicosia tried to control for built environments, but even when they did, the effect of the community remained significant.

In reality, the bright line between physical and social environments is a little fuzzier than we might like. People make the environments in which they live. Measuring the relevant properties of a built environment is challenging. And even though this is an elegant natural experiment, it’s still an observational study. The authors acknowledge that unobserved confounders leave room for uncertainty.

Despite that uncertainty, the big picture is pretty clear. Where you live, your family, and your friends can have an effect on your health and weight. So the challenge is to understand how to ensure that the effect can be positive.

Click here for the study, here for an editorial, and here for more on social contagion

Something in the Air, photograph © Xavier Donat / flickr

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January 26, 2018

One Response to “Are People Catching Obesity from Friends and Neighbors?”

  1. January 26, 2018 at 11:28 am, David Stone said:

    I’d vote for “people in the community”; a sort of “when in Rome” or peer pressure effect, about eating behaviors and whether it’s OK, or even preferable, to “let yourself go”. My lean partner who is not underweight by any clinical standard, tends to get comments such as “You’re so underweight!” when visiting her puffier relatives in Florida. No fat-shaming there. Just the opposite. And for many people, eating more is not much of a burden.