UC Berkeley

Importance

Annually, US schools screen millions of students' body mass index (BMI) and report the results to parents, with little experimental evidence on potential benefits and harms.

Objective

To determine the impact of school-based BMI reporting on weight status and adverse outcomes (weight stigmatization and weight-related perceptions and behaviors) among a diverse student population.

Design, setting, and participants

Cluster randomized clinical trial. The Fit Study (2014-2017) randomized 79 California schools to BMI screening and reporting (group 1), BMI screening only (group 2), or control (no BMI screening or reporting [group 3]) in grades 3 to 8. The setting was California elementary and middle schools. Students in grades 3 to 7 at baseline participated for up to 3 years. A modified intent-to-treat protocol was used. Data analysis was conducted from April 13, 2017, to March 26, 2020.

Interventions

School staff assessed BMI each spring among students in groups 1 and 2. Parents of students in group 1 were sent a BMI report each fall for up to 2 years.

Main outcomes and measures

Changes in BMI z score and in adverse outcomes (based on surveys conducted each fall among students in grades 4 to 8) from baseline to 1 and 2 years of follow-up.

Results

A total of 28 641 students (14 645 [51.1%] male) in grades 3 to 7 at baseline participated in the study for up to 3 years. Among 6534 of 16 622 students with a baseline BMI in the 85th percentile or higher (39.3%), BMI reporting had no effect on BMI z score change (-0.003; 95% CI, -0.02 to 0.01 at 1 year and 0.01; 95% CI, -0.02 to 0.03 at 2 years). Weight dissatisfaction increased more among students having BMI screened at school (8694 students in groups 1 and 2) than among control participants (5674 students in group 3). Results of the effect of BMI reporting on other adverse outcomes were mixed: compared with the control (group 3), among students weighed at school (groups 1 and 2), weight satisfaction declined more after 2 years (-0.11; 95% CI, -0.18 to -0.05), and peer weight talk increased more after 1 year (0.05; 95% CI, 0.01-0.09); however, concerning weight control behaviors declined more after 1 year (-0.06; 95% CI, -0.10 to -0.02).

Conclusions and relevance

Body mass index reports alone do not improve children's weight status and may decrease weight satisfaction. To improve student health, schools should consider investing resources in evidence-based interventions.

Trial registration

ClinicalTrials.gov Identifier: NCT02088086.