Kent Bottles: Is Obesity Spread Among Friends and Acquaintances like a Flu Virus?

September 14, 2009 at 11:08 am 2 comments

Ever since I got interested in how people get jobs through weak connections with acquaintances and not close friends and relatives as described years ago by Granovetter, network theory has fascinated me.  The Kevin Bacon Game was one of my favorites until researchers discovered that Kevin Bacon was not the most connected actor in Hollywood movies.  The whole subject became even more relevant, of course, with the Internet and social media.

Up until now, my four favorite books on the subject have been Mark Granovetter’s Getting A Job:  A Study of Contact and Careers (University of Chicago Press, 1974); Albert-Laszlo Barabasi’s Linked: How Everything is Connected to Everything Else and What It Means (Penguin, 2003); Steven Strogatz’s The Emerging Science of Spontaneous Order (Hyperion, 2003); and Duncan J. Watts’ Six Degrees:  The Science of a Connected Age (Norton, 2003).

My new favorite book is Nicholas Christakis’ and James Fowler’s Connected, and I have not even read it yet.  There work on the emerging science of social contagion may well be transformative for medicine and public health, and a good overview can be read in The Sunday New York Times Magazine article by Clive Thompson titled “Is Happiness Catching?” (September 13, 2009) ( By analyzing the famous Framingham Heart Study, they were able to map 5,124 subjects for a connection web of 53,228 ties between families, friends, and co-workers.

Obesity appears to spread among friends like a virus. “When a Framingham resident became obese, his or her friends were 57% more likely to become obese too.”  “A Framingham resident was roughly 20% more likely to become obese if the friend of a friend became obese.”  “You may not know him personally, but your friend’s husband’s co-worker can make you fat. And your sister’s boyfriend can make you thin.”

This process seems to also work for drinking, smoking, loneliness, and happiness. Christakis and Fowler believe that “these behaviors spread partly through the subconscious signals that we pick up from those around us, which serve as cues to what is considered normal behavior.”

Network experts are intrigued by this work, but they caution that social contagion may not be causing the spread of these social behaviors.  Homophily, the tendency of people to hang out with friends who are alike, could be causing the effect.  A shared environment could also be the cause of the spread, instead of a social contagion.

Jason Fletcher is a critic of the social contagion work.  His attempt to investigate social contagion theory has led him to demonstrate apparently contagious conditions that make no sense: acne, height, and headaches.  Fletcher seems to believe in social contagion effects, but he does not think much of Christakis’ and Fowler’s work.  Whether we are dealing with inside academic politics or a real weakness of the approach is up for debate as far as I can tell.

The exciting thing about the subject for me is the possibility of changing the way we think about public health.  “For most of us, within three degrees we are connected to more than 1,000 people – all of whom we can theoretically help make healthier, fitter, and happier just by our contagious example. ‘If someone tells you that you can influence 1,000 people,’ Fowler said, ‘it changes your way of seeing the world.’”

Entry filed under: Health Care Redesign. Tags: .

Gary Oftedahl: Learning Something from “Nutting” Gary Oftedahl: Shared Decision Making–is it really?


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