Center for Communications, Health and the Environment
Summer 2009 Vol. 4, Issue 1
Developed and Developing Nations Face Obesity Challenge

Is Obesity Contagious?

Social networks may be the catalyst behind obesity’s rapid spread. 

Source: Permission requested. http://thesituationist.wordpress.com/2007/
09/05/ common-cause-combating-the-

While genes and environment provide the raw materials for weight gain, researchers report that friends, particularly close friends, may have the greatest influence on one’s weight. 

In fact, a person’s chances of becoming obese increase by 57 percent if he or she has a friend, near or far, who becomes obese – and the odds triple if that friend is mutually close, a seminal study reveals.  Meanwhile, family members seem to have less impact, with obese siblings and spouses increasing the likelihood of obesity in their relatives by 40 and 37 percent, respectively. 

Persons of the same sex have relatively greater influence on each other than those of the opposite sex, and the status of immediate neighbors did not affect the chance of weight gain in study participants.  The same effect seems to occur for weight loss, but since most people were gaining, not losing, weight over the course of the study, the results are inconclusive for this variable.

The study, published in July 2007 in the New England Journal of Medicine and referenced extensively since then, was based on a detailed analysis of a social network of more than 12,000 people. This population had been closely followed for 32 years, from 1971 until 2003 (via the federally funded Framingham Heart Study), and their relationships, as well as weight history, were well-documented over time and known to investigators.

Study results indicate that obesity may be “a kind of social contagion” that spreads like a virus through networks of close contacts, note principal investigator Dr. Nicholas Christakis, a physician and professor of medical sociology at Harvard Medical School, and his colleague, James Fowler, an associate professor of political science at the University of California, San Diego.

Christakis and Fowler suggest that this spread may have to do less with behavioral imitation and more with a change in social norms regarding the acceptability of obesity.  In short, not only do friends influence what we eat and the activities and lifestyles we choose, they may also affect our perception of fatness.  So when a close friend becomes obese, fatness in general and personal weight gain in particular may become more acceptable, and less actively avoided as a result.

This unique analysis may shed light on how and why people have gotten so fat so fast in recent years.  It also may help to short-circuit the effects of social networks on weight gain going forward – and enable us to incorporate the strong bonds of friendship to fight, rather than foster, fat.

Read More:
Lead Article: Obesity and Overnutrition Trump Undernutrition in Newly Affluent Nations
In the Spotlight: The Economics of Obesity
CECHE News: CECHE Promotes Healthy Hearts
Also Noted: Is Obesity Contagious?

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