Weight Loss Can be Contagious, Study Suggests

Is weight loss “contagious”? According to a new study published online in the journal Obesity, teammates in a team-based weight loss competition significantly influenced each other’s weight loss, suggesting that shedding pounds can have a ripple effect.

Researchers from The Miriam Hospital’s Weight Control and Diabetes Research Center and The Warren Alpert Medical School of Brown University found that team members not only achieved similar weight loss outcomes, but participants who said their teammates played a large role in their weight loss actually lost the most weight.

“We know that obesity can be socially contagious, but now we know that social networks play a significant role in weight loss as well, particularly team-based weight loss competitions,” said lead author Tricia Leahey, Ph.D., of The Miriam Hospital and Alpert Medical School. “In our study, weight loss clearly clustered within teams, which suggests that teammates influenced each other, perhaps by providing accountability, setting expectations of weight loss, and providing encouragement and support.”

Obesity remains a common, serious and costly disease in the United States. About one-third of American adults are obese, according to the Centers for Disease Control and Prevention, and no state has met the nation’s Healthy People 2010 goal to lower obesity prevalence to 15 percent. Obesity and its associated health problems, including heart disease and diabetes, continue to have a significant economic impact on the U.S. health care system, costing the nation hundreds of billions of dollars each year.

To promote cost-effective weight loss initiatives, online team-based weight loss interventions are increasing in popularity as a way to encourage weight loss in large groups of people. The current study is the first to examine the effects of teammates and social influence on individual weight loss during one of these weight loss competitions.

Brian Wansink, an author of more than 100 academic articles and books on eating behavior, has found that when we are with people we enjoy, such as friends, we often lose track of how much, how fast and how long we are eating for. It seems when we are with others we tend to mimic the speed at which they eat and how much they eat.

Similarly, a new study published in the American Journal of Public Health suggests that obesity spreads socially not because friends have shared ideas about acceptable body size, but rather because they share environments and carry out activities together that may contribute to weight gain.

In other words, shared social behaviors, such as eating out at restaurants, and shared surroundings, likely play a bigger role in the obesity "friend effect" than do shared social norms.

Researchers interviewed 101 women and 812 of the their friends and family members (both men and women) and calculated the Body Mass Index for everyone in the study. The initial women in the study were 2.4 times more likely to be obese if their friends were obese. And they were 3.6 times more likely to be obese if their close friends were obese which confirms earlier findings that obesity spreads in social networks.