School-based nutrition policies, but not physical activity policies, limit BMI increases among middle school students.

Healthier school environments can benefit students, and school wellness policies may result in meaningful enhancements. Schools participating in federal child nutrition programs must implement wellness policies as mandated by law. The primary study objective is to assess effectiveness of implementing school-based nutrition and physical activity policies on student BMI trajectories.

Setting/participants

Twelve randomly selected schools in an urban district. Students were followed for 3 years through middle school, fifth to eighth grades (2011–2015, n=595 students, 92.3% participation, 85.2% retention).

Intervention

Specific to randomized condition, support was provided for implementation of nutrition policies (e.g., alternatives to food-based rewards/celebrations) and physical activity policies (e.g., opportunities for physical activity during/after school).

Results

Analyses followed intention-to-treat principles, with planned secondary analyses (conducted 2016–2018). Students at schools randomized to receive support for nutrition policy implementation had healthier BMI trajectories over time (F=3.20, p=0.02), with a greater magnitude over time and cumulatively significant effects 3 years post-intervention (β=–2.40, p=0.04). Overall, students at schools randomized to receive the nutrition intervention had an increase in BMI percentile of <1 3="" activity="" all="" and="" at="" ate="" behavioral="" between="" beverages="" bmi="" compared="" condition="" conditions="" consumed="" correlates="" difference="" eighth="" em="" examining="" fast-food="" fewer="" foods="" frequently="" grade="" implementation.="" in="" increased="" less="" no="" nutrition="" other="" percentile="" physical="" policy="" randomized="" restaurants="" schools="" student="" students="" sugar-sweetened="" the="" there="" those="" to="" unhealthy="" was="" whereas="" with="" without="">p

<0 .03="" p="">

Conclusions

This cluster randomized trial demonstrated effectiveness of providing support for implementation of school-based nutrition policies, but not physical activity policies, to limit BMI increases among middle school students. Results can guide future school interventions.