A study published in the New England Journal of Medicine claims that obesity spreads through social networks. This means that if your friends put on weight, you’re also more likely to put on the pounds. While family members or one’s spouse can affect your tendency to put on weight, the greatest influence are from friends — even if they are geographically distant.

“It’s spreading through ideas about what appropriate behaviors are, or what an appropriate body image might be. If I see you gaining weight, and I respect you, and want to emulate you in other ways, that changes my ideas about what is an acceptable body size. I think, ‘All my buddies are getting obese, so it’s OK for me to be obese too’ And even if you’re 1,000 miles away, or I only see you once a year, that’s enough to transmit the norm.” It’s really about creating acceptable norms for eating or lifestyle behaviors, as well as what constitutes an acceptable body image.

This is an important piece of the puzzle in what is considered the greatest public health hazard in the U.S. today. Now there is empirical evidence that the “mental dimension” of a complicated problem (i.e., weight gain) is also caused by a sociological phenomenon — on top of a media culture already bombarding us with cues to overeat the wrong foods.