Adolescent Body Mass Index and Exposure to Peers with Overweight and Obesity: A Structural Equation Model Approach to Longitudinal Network Data.

<b><i>Purpose:</i></b> Considerable evidence has shown that social networks influence a wide variety of health behaviors. This study investigates whether having friends with overweight/obesity in one's social network (network exposure) can predict changes in body mass index (BMI) throughout high school in a diverse urban population of students. <b><i>Methods:</i></b> Racially and ethnically diverse students from five high schools in Los Angeles County were surveyed at four time points throughout high school from 2010 to 2013 (<i>N</i> = 2091). Surveys included questions on students' social networks, demographics, and health-related information. BMI and weight categories were calculated for all students who provided height and weight information (∼50%). A latent growth curve model was used to assess the growth trajectory of BMI and the time-varying effect of network exposure to friends with overweight/obesity while controlling for demographic covariates. <b><i>Results:</i></b> Hispanic students had a significantly higher initial BMI compared with non-Hispanic students (<i>p</i> &lt; 0.01). There was a significant positive slope for time on BMI growth (<i>p</i> &lt; 0.01). Greater personal network exposure to friends with overweight/obesity was associated with a significant 0.65-point average increase in BMI (<i>p</i> &lt; 0.05) at the first follow-up time point (T2) and a significant 0.62-point average increase in BMI (<i>p</i> &lt; 0.01) at the last follow-up (T4) while controlling for covariates. <b><i>Conclusions:</i></b> Using structural equation modeling to understand the relationship between BMI and social networks, we found that increased network exposure to peers with overweight/obesity is associated with higher individual BMI, demonstrating that friendships may influence adolescents' weight status over time.