Is there evidence that friends influence body weight? A systematic review of empirical research

Researchers and policymakers from diverse fields are engaged in efforts to understand the biological and social causes of obesity in order to develop policies, interventions, and recommendations to stop or reverse increases in obesity. One potentially promising approach is to harness influence from social contacts. An important foundation for this approach involves critically analyzing available data regarding whether and how body weight can be affected by close social contacts, especially friends. This systematic review examines evidence from published studies addressing the influences of friends on body weight. The majority of the sixteen studies conclude that there is evidence of influence: six reported that friends influence body weight and ten reported evidence of influence in some circumstances or specifications. However, this literature sheds little light on mechanisms of influence. There is limited evidence that friends’ communication about weight is associated with weight status and no compelling evidence that friends’ behaviors affect one’s weight. Many of the studies best designed to examine influence were the ones that did not explore mechanisms of influence. A priority for future research is to understand how, when, and how much friends affect the risk of obesity.

► Sixteen peer-reviewed studies examined whether friends influence body weight, obesity and weight change.
► All studies reported significant associations between friends in body weight by at least one measure.
► Most studies are not able to establish causality between friends’ body weights.
► There is only weak evidence for the pathways through which friends may be influential.
► The majority of studies are based on data from adolescents, with limited information on other ages.