Is Obesity Contagious?

Have you ever noticed that many friends, spouses, and siblings seem to be of similar size? It’s not your imagination. Having a friend, sibling or spouse that is obese could increase your chances of being obese.

Researchers at the Harvard Medical School and University of California studied more than 12,000 people over a 32-year period and found the risk of being obese was increased by 57% if a friend was obese, by 40% if a sibling was obese, and by 37% if a spouse was obese. Their findings were published in the July 26th edition of The New England Journal of Medicine.

People of the same sex were more likely to have a greater influence on each other. As well, the closer the friendship, the more likely the friends influenced each other’s size. Even when close friends lived in different geographical areas they tended to influence each other’s weight, ruling out the possibility that these effects could be solely contributed by similar lifestyle and environmental factors. Also, having obese neighbours did not contribute to obesity.

Obesity may spread in social networks in a variety of ways. The researchers suggest that when people are surrounded by others that are overweight, they change their opinion about acceptable body size. Author Nicholas Christakas states: “It's not that obese or non-obese people simply find other similar people to hang out with…People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads.” Christakas stresses that factors such as lack of exercise or poor nutrition are not unimportant. Rather, he is suggesting that attitudes about acceptable body size can spread quickly throughout groups.

If you’re finding that others who are overweight are influencing you, don’t panic and avoid your overweight friends and family members. The researchers are not suggesting people sever ties with overweight friends. Rather, if you want to lose weight or become more active, try to convince overweight friends to do so as well. The researchers found that if an obese friend or family member loses weight, others close to them tend to lose weight. If you are serious about losing weight, it may also be helpful to enlist support from people that are of normal weight.

References

Christakis and Fowler (2007). The spread of obesity in a large social network over 32 years. The New England Journal of Medicine; 357(4): 370-379.

Obesity ‘contagious’, experts say. (2007). BBC News (online). Available from http://news.bbc.co.uk/1/hi/health/6914397.stm [Cited July 26, 2007].