People who hang out with friends heavier than they are tend to gain weight. Those who socialize with leaner friends tend to maintain their weight, or even lose a few pounds.

But why?

Is it that friends influence our behavior? Or do we simply tend to have friends that resemble ourselves—the birds of a feather flock together effect.

To find out, researchers looked at students from two high schools. One school is rural and mostly white. The other is urban, with a racially mixed student body. The researchers analyzed the students’ body mass and social networks.

They found that overweight students who had lean friends had a 40 percent chance of dropping weight within a year, versus only a 27 percent chance of gaining weight during that time. But if borderline obese students had obese friends there was a 56 percent chance that they’d gain weight during the year, and only a 15 percent chance they’d drop some pounds. The finding is in the journal Public Library of Science ONE.

The researchers conclude that social influence is indeed a big factor in weight loss and gain. Because you’re not what you eat—you’re who you eat with.  

—Christie Nicholson

[The above text is a transcript of this podcast.]