Can friends influence your body weight?

OK people, hands up if you think there’s nothing better than a good friend turning up on your toadstool, unless it’s a good friend with chocolate! I’m thinking that there will be quite a lot of hands in the air right now. Oh yes, if your best friend is about to eat half a chocolate bar in front of you, well it would be rude not to have the other half when offered, surely?

Friends can influence our health behaviours. It might be in a negative way where we feel pressure to drink, take drugs or eat unhealthily, for example. Or it could be in a positive way where they encourage and motivate us to take part in sport, dieting or making sensible food choices.

Understanding whether and how body weight can be affected by close social contacts, especially friends, is the subject of a systematic review carried out recently. It seems that the closer the connection the stronger the possibility for influence and ultimately for developing an important resource in interventions for obesity. The aim of the review was to examine the evidence of friendship influences on weight, the strength of these findings and possible mechanisms through which friendship influences may occur. After a search of relevant databases they found sixteen peer-reviewed studies for inclusion that examined whether friends influence body weight, obesity and weight change. This is what they found:

  • Six studies reported significant associations consistent with friendship influences on body weight
  • Ten reported mixed results depending on the relationship under study or the model specification
  • Body weight was more strongly associated between friends than between siblings and partners and stronger between best friends than casual friends
  • Same sex friends appear to influence weight more than opposite sex friends
  • Limited findings suggest that friends’ communication about weight is associated with weight status
  • There is no evidence that friends’ behaviours affect one’s weight


  • Due to the variety of measures and study designs employed with multiple measures of body weight and of friendship in diverse populations, it was not possible to carry out a meta-analysis
  • Some of the analyses suggest that associations between friends’ weights are driven by the tendency to associate with similar people (homophily) or shared environments rather than influence
  • The majority of studies are based on data from adolescents, with limited information on other ages
  • Many of the studies findings were limited as they relied on reports from the subject about his or her friends. However, the strongest associations were observed in studies that relied on direct measures of the subject and their friends’ weights

The authors concluded:

Research on social influences on body weight has provided some insights into the possible existence of influences and their potential usefulness in programs. At the same time, there is much to learn about how friends influence each other, under what circumstances, the mechanisms through which influences can occur, and the ways in which programs can involve friends to promote healthy weight.

William Shakespeare once said, ‘A friend is one that knows you as you are, understands where you have been, accepts what you have become, and still, gently allows you to grow.’

Hopefully not in girth though!  Come on all you best friends out there, you have your friends’ best interests at heart and are probably the most capable of providing the right kind of motivation to get someone to change their unhealthy behaviours.  Give it a go!


Solveig A. Cunningham, Elizabeth Vaquera, Claire C. Maturo, K.M. Venkat Narayan, Is there evidence that friends influence body weight? A systematic review of empirical research, Social Science & Medicine, Volume 75, Issue 7, October 2012, Pages 1175-1183 [Elsevier]