Are Your Friends Making You Fat?

Remember the lunch scene in Mean Girls, when Janis Ian explains the social layout of the high school cafeteria? Each clique has its own designated table, and “girls who eat their feelings” sit at one, sub sandwiches in hand, while a group of “girls who don’t eat anything” sit around another and split a Diet Coke. While the scene’s meant to be satirical, it turns out there’s some truth to it: Our friends influence our weight, according to a recent scientific study published by the Public Library of Science ONE.

For years, researchers have debated the effect of social influence on weight gain. Do our friends’ numbers on the scale really influence our own? Or do we simply have a tendency to select friends who are similar to ourselves in many ways, including pants size?

To answer it, researchers studied students from two Midwestern high schools. One school was rural and had mostly white students. The other was urban, and had a racially diverse student population. Researchers looked at the students’ body mass index (BMI), and two behaviors linked to weight gain: time in front of a computer or television screen, and playing active sports or not. They then compared these factors among the students’ social networks.

While students were predisposed to select friends of a similar size, they also showed a tendency to gain or lose weight in order to match the average BMI of their friends. Overweight students with thinner friends had a 40 percent chance of losing weight within a year, while overweight students with overweight friends had only a 15 percent chance of shedding pounds during that time.

The influence is even more likely to operate in a detrimental direction. Overweight students with overweight friends had a 56 percent chance of gaining weight within a year. Even more alarming: Healthy-weight students with overweight friends had a 51 percent chance of packing on extra pounds.

Why?

It’s not exactly clear. The study indicated that our friends tend to influence how much time we spend sitting in front of a screen and playing active sports. It also seems possible that our friends shape our idea of what an acceptable weight is.

So maybe it’s time to ditch those couch potato friends of yours and seek out more active pals. Your waistline will thank you for it.