Is Being Fat Contagious?

Miriam Nelson’s new book is based on the notion that your weight is all about who you know

Did you know there is a growing body of evidence that being fat is contagious?

In 2007, researchers at Harvard Medical School released a study that found a person’s chance of becoming obese appeared to climb by 57 percent if a friend of the same sex was obese. Among close mutual friends, the risk of obesity climbed by 171 percent.

A 2008 study found similar results among adolescents, with a teen’s body weight tending to be similar to that of his or her closest friends. This was especially true among girls.

A more recent study out of Brown University found that overweight and obese men and women, ages 18 to 25, were more likely to have romantic partners, best friends and casual friends who were also overweight.

Why would this be? One theory is that as the size of our friends creeps up, we change our idea of what’s socially acceptable.

“I believe that these changing norms have had a profound influence on the rapid spread of obesity,” Miriam Nelson writes in her new book, The Social Network Diet: Change Yourself, Change the World (FastPencil Premiere, 2011), co-authored with Jennifer Ackerman.

But if being fat is contagious, so might being healthy. That is the premise of Nelson’s book, which, despite its high-tech name, has little to do with the Internet and more to do with the network of friends, family, neighbors and colleagues who get us through our daily lives. If the people around us are eating right and exercising, we’re likely to do the same.

Nelson had that idea in mind when she started the Change Clubs, which use the power of women working together to make their communities healthier. While she’s starting with just eight Change Club sites across the nation, she’s hopeful the idea will spread to become a vast network of women supporting each other and their towns.

Julie Flaherty can be reached at


Back to Top