Results of heterogeneity analysis.

The prevalence of overweight and obesity among adolescents has been increasing steadily. This study aims to investigates the causal effect and underlying mechanisms between Internet use and body weight among Chinese adolescents. Using data from China Health and Nutrition Survey (CHNS) spanning from 2004 to 2015, the analytical sample includes 3054 participants (aged 11–19, 48% females). We exploit ordinary least squares (OLS) and two-stage least squares (2SLS) models, obtained causal effect of Internet use on body mass index (BMI), overweight and obesity among adolescents. We find a significant positive effect of Internet use on BMI (β = 0.499, p < 0.05) and probability of overweight (β = 0.061, p < 0.05). Specifically, Internet use increases BMI by 2.56%, and increases the probability of being overweight by 6.1%. But no evidence shows that Internet use significantly increases the probability of obesity (p > 0.1). The mechanism is that Internet use increases sedentary activities (mainly screen time) and food consumption behavior, which results in an imbalance between energy intake and expenditure that in turn increases BMI and overweight. Furthermore, the longer the time spent playing games online, the greater the probability of adolescents being overweight (β = 0.012, p < 0.1), whereas time spent watching movies online, surfing online, and chatting online is not significantly associated with body weight. Heterogeneity analyses show that the adverse effects of Internet use on adolescents’ body weight is more pronounced in rural areas and among the male group. This study suggests that reducing time spent playing games online, and increasing physical activity and cultivating healthy eating behaviour can reduce the risk of overweight and obesity in adolescents.