Are Your Friends Making You Fat?

A new study published in PLoS suggests that your friends have a strong influence on your body-weight.

The researcher found that “students were more likely to gain weight if they had friends who were heavier than they were. Conversely, students were more likely to get trimmer — or gain weight at a slower pace — if their friends were leaner than they were”.

And while these observations aren’t exactly new, this study was “designed to determine the reason why obesity and related behaviors cluster in social networks”.

  • Is it because behaviors are contagious? – the social influence hypothesis
  • Is it because fit students have fit friends and fat students have fat friends? – the homophily hypothesis

Using statistical analysis, the researchers crunched the data obtained from two studies of over 1700 high school students and determined that “part of the reason why obesity clusters in social networks (aka friends) was indeed due to the way students selected friends” – jocks hang out with jocks, etc…

However, they also found that this effect was not entirely responsible for the link between obesity and a student’s circle of friends.

For example, if a borderline overweight student at Jefferson High School had lean friends (average BMI 20), there was a 40 percent chance the student’s BMI would drop in the future and a 27 percent chance it would increase. But if a borderline overweight student had obese friends (average BMI 30), there was a 15 percent chance the student’s BMI would decrease and a 56 percent chance it would increase.[/box][box type=”important”]The researchers concluded that social influence “tends to operate more in detrimental directions, especially for BMI; a focus on weight loss is therefore less likely to be effective than a primary prevention strategy against weight gain. Effective interventions will be necessary to overcome these barriers, requiring that social networks be considered rather than ignored.”

NOTE – This study is not saying that kids with fat friends are doomed to becoming overweight themselves. And even if it did, the study is observational and based on self-reported data – which makes me a little skeptical about the whole thing.

Nevertheless, I think the study does shine a light on the idea that we are all susceptible to peer pressure and usually not for the better.


Douglas Robb

Doug Robb is a personal trainer, a fitness blogger and author, a competitive athlete, and a student of nutrition and exercise science. He's also the co-founder of the Hive Health Media. Since 2008, Doug has expanded his impact by bringing his real-world experience online via the health & fitness blog – Health Habits.

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