Teammates in a dieting challenge significantly improved each other's outcomes, suggesting that shedding pounds can have a ripple effect.

PROBLEM: Obesity remains a common, deadly, and costly disease in the U.S. It affects one in three American adults and its associated health problems, including heart disease and diabetes, cost the nation hundreds of billions of dollars each year. Can team-based weight loss interventions help?

METHODOLOGY: Researchers from Brown University analyzed the results of the 2009 Shape Up Rhode Island campaign, a 12-week online weight loss competition where participants joined a team and competed in three divisions: weight loss, physical activity, and pedometer steps. The contest included 3,330 overweight or obese people or 987 teams.

RESULTS: Competition outcomes were most determined by the teams the participants were in. Those who lost clinically significant amounts of weight or at least five percent of their initial body weight tended to be on the same teams. Members who reported more teammate influence also increased their odds of achieving this level of weight loss by 20 percent.

CONCLUSION: Social influences can fuel weight loss.

IMPLICATION: Being surrounded by the right people when dieting matters. Lead author Tricia Leahey explains in a statement that they may provide accountability, help set expectations of weight loss, and provide encouragement and support.

SOURCE: The full study, "Teammates and Social Influence Affect Weight Loss Outcomes in a Team-Based Weight Loss Competition," is published in the journal Obesity.

Image: Everett Collection/Shutterstock.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.