Objective   To explore the effect of school-based health education on dietary behavior combined with physical activity intervention on body mass index (BMI) and obesity rate among urban junior high school students in China and to provide evidences for obesity control among adolescents.

  Methods   A total of 1 491 students of first and second grade were selected with random sampling from 10 junior high schools in the urban areas of Tianjin, Neijiang, and Dalian city for the study in September, 2015. Demographic data and body measurement indicators were collected prior to the initiation of a 10-month intervention program. The students were then randomly attributed to a comprehensive intervention group (n = 720) with health education and physical activity integrated intervention and to a control group (n = 771) with only lectures and reading material for health education. A post intervention survey was performed to obtain the information on knowledge, behavior of and attitude towards healthy life style, and physical measurement was also undertaken.

  Results   The average BMI of obese students in the intervention group decreased from 30.1 ± 5.8 kg/m² to 28.9 ± 3.4 kg/m²; while that of obese students in the control group decreased by only 0.5 kg/m² after the intervention. The mean BMI of male obese students in the intervention group was 28.6 ± 3.3 kg/m² after the intervention, which was significantly lower that that (30.0 ± 7.3 kg/m²) before the intervention, and the decline was significantly greater than that (0.6 kg/m²) of their counterparts in the control group (P < 0.05). No significant intervention effect was observed in the female students in both the case and the control group (both P > 0.05). After the intervention, the sedentary time was reduced by 0.1 hour per weekday and the number of days with intakes of vegetables and fruits was increased by 0.6 day per week among the students of the case group but no variation in sedentary time and vegetable and fruit consumption per week were observed among the students of control group, with significant differences (both P < 0.05).

  Conclusion   Health education and physical activity integrated intervention is helpful to promote physical activity level and could significantly reduce obesity status among urban junior high school students, especially among the boy students, but the intervention effect differs by gender.