Why your friends can make you fat

Our tendency to match the behaviour of our social circle means you are who you work and play with.

(Photo: Gary Tramontina/New York Times)

Your social network can make you feel connected, keep you learning, even help you find a job. But it can also put your health at serious risk.

When people hear “social network,” they tend to think of Facebook. But we’re all part of many networks in our off-line lives—of friends, family, co-workers. Scientists have long been fascinated by how patterns of human interaction affect individual lives. Why do the rich tend to get richer, for example? One reason is that they join networks of better-off friends and gain access to opportunities to earn more. How do you control a highly contagious disease like SARS? Epidemiologists track the social connections of infected people as they try to isolate the disease.

Nicholas Christakis and James Fowler, American scientists and authors of the 2009 bestseller Connected, have demonstrated that how we feel, what we know, whom we marry and whether we fall ill all depend on the ties that bind us. Our decisions regarding whom we connect with, how many people we connect with—and how many people they connect with—can subtly or dramatically influence our desires and actions. That includes our attitude toward food and physical activity. Christakis and Fowler found, for instance, that a person’s risk of becoming obese triples if someone in their circle becomes obese. “We discovered that if your friend’s friend’s friend stopped smoking, you stopped smoking,” they write. “Eventually, we realized that there were fundamental rules.” It seems obesity and smoking can be contagious.

Most of us have seen such forces at work in our lives. If you travel frequently on business in teams, you may have noticed how group norms form over time. If a few colleagues have three or four drinks every evening or dessert at dinner, others feel liberated to indulge in ways they might not if they were alone. Gradually, this becomes the norm for the whole team.

The same unconscious, instinctive desire to copy others’ behaviour is at play when you put on 20 pounds after falling in with a group of friends who are overweight. Conversely, if you’re out of shape and are surrounded by fit people, you realize your condition is not normal and become motivated to get active.

I have clients whose weight and lifestyle put them at risk of diabetes. Constantly on the road, they eat rich meals, work long hours and don’t exercise. I’ve come to meet some of their friends. Together in their social networks, they reinforce each others’ bad habits. I hear the same reason all the time: “It’s just my way of life these days.”

What can we do to change unhealthy behaviour? Ditching your friends and changing jobs to stay healthy is a non-starter. But we need to look for ways to take control of the situation. Acknowledging that we’re sliding into destructive patterns based on the influence of others is a critical first step. The second is to actively work at changing group norms. Take the leadership skills you muster at the office and apply them to changing behaviour. Many of my clients now ensure breakfast meetings offer fruit and yogurt rather than doughnuts and muffins. They carve out time on business trips for a run or a walk, and invite colleagues to join. One executive who had experienced the benefits of certain supplements to keep up his energy and immune system on stressful trips decided to offer supplement packs to his executive team during a week of round-the-world town-hall meetings.

You should also consider ex­­panding your network to include people whose habits you want to emulate. Running groups, exercise buddies, peer weight-loss programs—all are good ways to tap into the positive power of social networks. It’s little wonder that the number of cycling teams and home yoga groups is rising: there’s no better way to reinforce your commitment than to be around others with similar goals.

Elaine Chin, M.D., M.B.A., is a founder and Chief Medical Officer of Scienta Health, an executive health practice.