Design of a school randomized trial for nudging students towards healthy diet and physical activity to prevent obesity: PAAPAS Nudge study protocol.

Objective: To evaluate the effectiveness of nudge activities at school on the students' body mass index (BMI).

Design: School-based factorial randomized community trial.

Setting: Eighteen public schools in the municipality of Duque de Caxias, metropolitan area of Rio de Janeiro, Brazil.

Participants And Intervention: The 18 schools will be randomized into 4 group arms: group 1-control (without any activity); group 2-will receive educational activities in the classroom; group 3-will receive changes in the school environment (nudge strategies); group 4-will receive educational activities and changes in the school environment. Activities will occur during the 2018 school-year.

Main Outcome Measure(s): The primary (BMI) and secondary (body fat percentage) outcomes will be assessed at baseline and after the study using a portable electronic scale with a segmental body composition monitor. The height will be measured by a portable stadiometer.

Analysis: Statistical analyses for each outcome will be conducted through linear mixed models that took into account the missing data and cluster effect of the schools.