Is Obesity Contagious?

By Michael Crupain, MD, MPH

The answer to that question, according to a well-publicized paper, published in the New England Journal of Medicine, is yes.  The article published in 2007 by Christakis and Fowler used data from the Framingham Study (a long running cohort study from which we have learned a lot about chronic disease and its risk factors) to construct social networks to investigate the relationship between obesity and friendship.  Using complex statistical methods, the authors argue that obesity is more likely to occur in a previously non-obese person if a close friend becomes obese and that this development of obesity is independent of their environment or a tendency of people to choose friends with similar attributes.

Today’s New York Times reports that another more recent paper is refuting the claims made by Christakis and Fowlers and states that the statistical reasoning they applied to their data does not allow them to draw the conclusions they have.  In this new paper, author Prof Lyons, is quite annoyed by what he believes is the improper use of statistics (something that happens far too often) and he writes that in their New England Journal of Medicine Paper, Christakis and Fowler in many cases should have drawn conclusions opposite to what they did.

Trying to understand the statistical arguments in either the original paper or the recent rebuttal by Lyons is not easy.  If professor Lyons is right, which he certainly may well be, the idea that obesity is “contagious” is still important to think about.  It also may be an idea that is quite reasonable to accept to some degree, despite being difficult to prove scientifically.     

People learn behaviors from other people.  Albert Bandura’s Bobo Doll experiment is probably the most well known example of learned social behavior.  His theories are used today by both public health experts and advertisers to model behaviors that in movies and TV shows to produce behavior change.  Companies pay huge sums of money for celebrity endorsements, which are meant to get people to change their behavior, because they work.  

These same principles should apply to learned behavior/imitation between friends.  This is quite well illustrated by teenagers who adopt the clothing, hairstyles, language, and mannerisms of their friends.  But it also happens in adults, who also adopt mannerisms, language, styles, and habits from people they spend time with.

One could argue that social networks and key influencers are an important part of the environment in which we live.  In addition to changing the physical environment to promote healthy weights we also have to change the social environment.  Understanding the dynamics of social networks and the power of key influencers may be helpful in helping create and maintain healthy social environments.