You Can Catch Weight Gain from Your Friends, According to New Study

A rush of recent news headlines has suggested that weight gain is “contagious.” Based on a study of military families published in late January, these headlines are both true and somewhat misleading without a closer read.

The study, which examined families from 38 military installations around the United States, looked at whether a person’s exposure to communities with higher rates of obesity might have a negative effect on the person’s own Body Mass Index — and the answer was yes. For every 1 percentage-point increase in the obesity rate of the county in which a person lives, the odds of that person being obese increase by 5%. In addition, the greater the length of exposure — the longer a person lives in that environment — the higher their likelihood of obesity.

And so the report concludes that, yes, obesity might be contagious. But it’s important to clarify that the report is not talking about a physical virus like the flu or chickenpox. It’s not an illness you can “catch” in the classic sense of the word.

What they’re talking about here is social contagion — the idea that various behaviors propagate through friends and family to become widespread within a social group. If your friend eats an extra donut, for example, you figure you might as well eat one too. Past studies have already shown this to be the case for behaviors such as smoking and even divorce. Obesity too has already been shown [ http://www.nejm.org/doi/full/10.1056/NEJMsa066082 ] to be socially contagious.

What’s different about this latest study, even if just subtly, is its extension to the local community at large, not just people within a limited social network.

The good news, though, is that it seems to cut the other way as well. Another new study has identified what it calls a “ripple effect” among spouses of dieters. Even when not consciously dieting themselves, the partners of successful dieters were found to have lost an average of 3% of their own body weight over the course of the six-month study.

“When one person changes their behavior, the people around them change,” says study author Amy Gorin of the University of Connecticut. “Spouses might emulate their partner’s behavior and join them in counting calories, weighing themselves more often, and eating lower-fat foods.”

And so while weight gain may be contagious, it seems that weight loss could be as well. A lot depends on the people you surround yourself with. Or better yet, maybe you could be the person who leads the change within your own social network.