Obesity Spreads Through Social Networks

Picture: Two girls

Obesity-risk is highest among
same-sex friends; © SXC

In a study of 12,067 people over a period of 32 years researchers from Harvard Medical School and the University of California (U.C.), San Diego have found that social networks have a marked influence on weight gain. For example, if a person’s close friend becomes obese, that person’s chances of becoming obese increase 57 percent; for siblings, increase is 40 percent; and for spouses, increase is 37 percent. The closer two people are in a social network, the stronger the effect. Interestingly, geographical distance between persons in a social network appears to have no effect.

The researchers found that gender played an important role in how these statistics broke down. In same-sex friendships, individuals experienced a 71 percent increased risk if a friend of theirs became obese. This pattern was also observed in siblings. Here, if a man’s brother became obese, his chances of becoming obese increased by 44 percent. Among sisters, the risk was 67 percent. Friends and siblings of opposite genders showed no increased risk.

Social connections seem to be key. Moreover, as Nicholas Christakis, MD, PhD, a professor in Harvard Medical School’s Department of Health Care Policy notes, “The fact that neighbours don’t affect each other and that geographic separation doesn’t influence the risk among siblings or friends tells us that environmental factors are not essential here.”

“Most likely, the interpersonal, social network effects we observe arise not because friends and siblings adopt each other’s lifestyles. It’s more subtle that that. What appears to be happening is that a person becoming obese most likely causes a change of norms about what counts as an appropriate body size. People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads”, he says.

MEDICA.de; Source: Harvard Medical School