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Martina M. Cartwright
Martina M. Cartwright Ph.D., R.D.

Are Your Friends Making You Fat?

How friends' habits influence body weight

Ok, so it’s August…are you struggling to keep your New Year’s Resolution to lose a few pounds or exercise more? Perhaps you might want to take “Friend-ventory” and find out who might be helping or hurting your journey towards adapting healthy lifestyle habits.

Friends are essential to developing and sustaining fitness habits that last. Research shows that dieters can achieve greater weight loss if partnered with supportive pals and exercisers are more motivated if paired with a buddy. And social support is essential to health; people with close friends experience less depression, have better immunity against colds and experience

Forty-three percent of Edelman survey respondents said that friends/family have the most impact on personal health lifestyle with 36% reporting that close social ties have the most impact on personal nutrition. About two thirds said they tried to change a negative health behavior, but half of them failed…why? Lack of on-going social support.

What’s scary is that your close friends, whether next door or across the country, can influence your weight. In 2007, researchers Christakis & Fowler published results from the Framingham Heart Study; they followed 12,067 subjects for over 32 years and found that a person’s chances of becoming obese increased by 57% if a friend became obese.

Gender was also important. The probability of obesity increased by 71% if friends were the same sex. All-male friendships resulted in a 100% increase in the chance of becoming obese whereas the female-female obesity risk was about 38%. Interestingly, friend weight had more of an influence than spouse weight. Among married couples, the spouse was 37% more likely to become obese if their partner became obese.

The landmark Christakis & Fowler study clearly demonstrated that friends, particularly of the same gender, had a profound influence on body weight, and that this influence was even stronger than that of siblings and spouses. Even more interesting was the fact that geographical distance was not a factor. It didn’t matter if the friend lived close by or across the country, people were more likely to tip the scales if their pals did too. This study suggested the “contagious” nature of obesity but failed to identify a cause.

Peer pressure may influence body size and health behaviors. Individuals may feel bullied into adapting the habits and routines of friends in order to fit in. Such is the case in adolescents where the pressure to conform is significant. Obesity often carries a social stigma and may trigger inappropriate weight loss behaviors in adolescent girls. Similarly in adults, Hruschka et al. reported that 25.1% of respondents would rather have severe depression than be obese. A shocking 14.5% said they’d rather be completely blind! Nevertheless, peer pressure appears to play a limited role in friend-friend obesity.

It's believed that social norms may be to blame, in part, for the contagious nature of weight gain among friends. Social norms governed things like acceptable body size, eating habits and exercise among friends and close associates. Social norms are learned from friends and family and may develop unconsciously.

The desire to mimic close mates is thought to enhance bonding and act as social super glue. Mimicking tightens subconscious bonds especially if we are dining together. Wansink reported in his book “Mindless Eating” that distracted dining causes over eating..and more people at the dinner table equals more eating and drinking. For example, people who ate with 7 or more friends consumed a whopping 96% more than if eating solo! Folks who eat together subconsciously mimic each other’s eating style so if somebody at your table is a fast eater, normally slow eaters will unconsciously increase eating speed too. The “pacesetter” sets the standard for how much is eaten and how fast.

This “monkey see, monkey do” action can be used as an impetus for change. Social norms are fluid and can be modified. If one person decides he or she wants to drop a few pounds by changing eating habits, then this may be contagious amongst the group. By changing the accepted norm, healthier eating behaviors are adopted. Such is the case with exercise habits. Positive reinforcement from close pals is associated with more physical activity, particularly in women.

So if you are looking to improve your health and drop a few pounds, take Friendventory. Friends can help or hurt your fitness journey. By modifying your own habits, you may spread wellness among your BFFs!

Christakis, N.A., & Fowler, J.H. 2007. The spread of obesity in a large social network over 32 years. New England Journal of Medicine. 357(4),370-379.

Edelman Health Barometer 2011. Findings.…; retrieved October 7,2011.

Hruschka, D.J., et al. 2011. Shared norms and their explanation for the social clustering of obesity. American Journal of Public Health. Epub ahead of print. May 5, 2011. Doi10.2105/ADPH.2010.300053.

Wansink, B.

About the Author
Martina M. Cartwright

Martina M. Cartwright, Ph.D., R.D., is an adjunct professor of Nutritional Sciences at the University of Arizona and an independent biomedical consultant.

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