Associations Between Leisure-Time Physical Activity, Diet Type/Kind of Diet, and Body Weight Status Among Austrian Secondary School Pupils

Background/Objectives: Overweight and obesity present major public health challenges during adolescence. This study aimed to examine the independent associations of leisure-time physical activity (exercise frequency and club sports participation) and kinds of diet with body mass index (BMI) percentiles and weight status among Austrian secondary school pupils. Methods: Data were drawn from the nationwide cross-sectional From Science 2 School study. A total of 8799 pupils aged 9–22 years (63.1% female) completed an online survey capturing sociodemographic factors, exercise frequency, club sports participation, and kind of diet (omnivorous, vegetarian, vegan). Self-reported height and weight were used to calculate age- and sex-specific BMI percentiles. Data were analyzed using ANOVA with Bonferroni adjustment for post hoc tests as well as multivariable logistic regression analyses. Results: Overall, 11.8% of the participants were classified as overweight or obese and 82% reported regular leisure-time exercise. Engaging in leisure-time exercise on ≥4 days per week was associated with a 48% lower likelihood of overweight/obesity, with the strongest protective effect observed among 10–12-year-olds. Additionally, a vegetarian diet was associated with lower BMI percentiles (p < 0.01) and a 41% reduced risk of overweight/obesity, with effects being particularly prominent in girls. Conclusions: High-frequency leisure-time exercise and plant-based diet types are independently associated with more favorable body weight outcomes in adolescents. Integrated school-based prevention approaches addressing both physical activity and plant-centered nutrition may offer optimal synergies for obesity prevention.