An experimental study reveals that the FTO gene and gender modify peer influence on body mass index

Research has shown that friends’ obesity statuses are correlated. However, it is difficult in observational data to test whether peer influence on obesity is causal. We conducted an experimental study of randomly-assigned... [ view full abstract ]

Research has shown that friends’ obesity statuses are correlated. However, it is difficult in observational data to test whether peer influence on obesity is causal. We conducted an experimental study of randomly-assigned college roommates to investigate peer influence on body mass index (BMI). We examined whether the FTO (fat mass and obesity associated) gene and gender modify peer influence. We found that women inheriting two risk alleles for obesity weigh about three pounds less if randomly assigned a frequently-exercising roommate than if randomly assigned a non-frequently-exercising roommate. This effect size is equivalent to about 60% of the FTO gene effect. Both women and men inheriting two risk alleles exercise more often if randomly assigned a frequently-exercising roommate. However, for men this increase in physical activity does not lead to a decrease in BMI, probably because men’s exercise motivation is often muscle building while women’s motivation is often weight control.