Find a Doctor
New Study Shows That Obesity Is Socially Contagious

New Study Shows That Obesity Is Socially Contagious


No, it’s not something you can catch from your coworker or from touching a door handle, but a recent study has prompted researchers to label obesity as “socially contagious.” Friends and other close social connections seem to have a big influence on whether an individual becomes obese.

The occurrence of obesity, characterized by having a body mass index (BMI) of 30 or more, has dramatically increased in the United States over the past 20 years. The new study shows that this increase may be due to a change in social norms.

According to the study, if you have a friend who is obese, you have a 57 percent chance of becoming obese yourself. For mutual friends – that is, two people who each consider the other a friend – the risk jumps to 171 percent. The numbers were much lower for siblings and spouses (40 percent for siblings and 37 percent for spouses), which led the researchers to conclude that same-sex friends had the biggest influence.

The study, conducted by James Fowler from the University of California San Diego and Nicholas Christakis from Harvard Medical School, involved the analysis of more than 12,000 adults who participated in the Framingham Heart Study. They used the data that was collected over a period of 32 years to map social connections and BMIs of each person in the group. In addition to finding that the group as a whole got heavier over time, they also found distinct clusters of heavier and lighter people.

“What appears to be happening is that a person becoming obese most likely causes a change of norms about what counts as an appropriate body size,” said Christakis in an article posted on the University of California San Diego website. “People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads.”

Social rather than geographical proximity seems to have the greatest impact. Fowler and Christakis point out that a friend who lives hundreds of miles away has the same influence on an individual’s chance of becoming obese as one who lives right down the street, showing that environmental aspects, such as having several fast food restaurants nearby, didn’t matter.

Does this research mean that we have a social responsibility to lose weight and get in shape for the sake of our friends’ health as well as our own? The researchers seem to think so.

“Other people are going to be looking to you, and so your health behaviors don't just affect you, they affect your friends as well,” said Fowler in a WebMD article posted in July, 2007. In their study, the researchers say that obesity should be approached as a public health problem, and that the power of social influence which seems to be advancing the obesity epidemic can also be used to combat it.

Fitness Can Be Contagious, Too

In their study, Christakis and Fowler claim that fitness and a healthy lifestyle can also be socially contagious. Just as unhealthy behaviors can spread from person to person, so can healthy behaviors. Essentially, you are more likely to adopt healthy behaviors if you have a friend or relative who is fit and healthy.

Ellen Rohan has observed this phenomenon on many occasions. As office administrator and bariatric liaison at Lite and Smart DIMENSIONS™, a surgical weight loss center in Orange County, California, she has seen many situations in which one person who has undergone weight loss surgery influences others to do the same.

“They see someone else having a healthy lifestyle and they want to adopt it themselves,” said Rohan. She recalls an entire family – mother, father, and two children – who underwent the surgery. First the mother had the surgery, and the rest of the family followed suit after they saw how it improved her life.

The same thing happens at fitness centers. Keith Kaplan, a senior sales counselor at LA Fitness, said that he sees many friends who come into the center to workout together. He added that having a workout buddy can help you stay on track: “I know it’s hard to stay motivated, and they can help push each other.”

The Cultural Aspect

Has a change in social norms in America led us to become so sedentary that our favorite pastime is sitting in front of the TV while eating mega-sized portions of junk food? It’s not so in other cultures. Consider these statistics: nearly 30 percent of Americans are considered obese compared to only 11 percent of the population in France.

In her widely popular book French Women Don’t Get Fat, author Mireille Guiliano describes her battle with weight issues. As a teenager, Guiliano came to the United States as an exchange student. During her year in Massachusetts, she dropped her French eating habits and exchanged them for the American way that included rich brownies, warm chocolate chip cookies, and eating on the run. She returned home 20 pounds heavier, which prompted her father to proclaim, “You look like a sack of potatoes!”

Guiliano eventually lost the extra weight, thanks to a family friend she calls Dr. Miracle. He re-introduced her to some “old French tricks,” mainly consisting of savoring small portions of high-quality food. In the French culture, she explains, people walk everywhere. They drink wine and eat bread, cheese, and other foods that are considered “fattening,” but they learn to savor it in small portions.

Is Change Needed?

None of this means that you should ditch your heavier friends for thinner ones, or, for that matter, move to France. But the research suggests that greater emphasis should be placed on changing our lifestyles, both for ourselves and for those around us. “When we help one person lose weight, we’re not just helping one person, we’re helping many,” asserted Fowler in the article for the University of California San Diego. “And that needs to be taken into account by policy analysts and also by politicians who are trying to decide what the best measures are for making society healthier.”

Want More Information?

Contact a Doctor Near You.