Using routinely collected growth data to assess a school-based obesity prevention strategy

Studies of school-based anti-obesity interventions have yielded inconsistent results. Using growth screening data from a school administrative database, we re-evaluated an obesity prevention strategy that was previously reported to have a beneficial effect on weight status of a sample of students in grades 5-7.

Ten K-8 schools (five control and five intervention) participated in a 2-year cluster-randomized trial of a multi-component nutrition education intervention. We obtained student height and weight data for 6 consecutive school years and imputed missing baseline and follow-up measurements (53% and 55%, respectively) and defined the target population based on the intent-to-treat principle. We analyzed changes in body mass index (BMI) Z-scores via mixed-effects linear regression and in the prevalence of overweight/obesity via conditional logistic regression. We also assessed incidence and remission of overweight/obesity and long-term effects.

We analyzed data for 8186 (96%) K-8 students in the 10 schools (4511 in intervention; 3675 in control). From baseline to the end of the intervention period, mean increases in BMI Z-score were 0.10 and 0.09 in the control and intervention groups, respectively (P=0.671). The prevalence of overweight/obesity increased by 3% in both groups (P=0.926). There was no significant intervention effect on the incidence or remission of overweight/obesity. Among 5469 students who attended study schools during both years of the intervention, there was no significant intervention effect. Furthermore, there was no long-term effect among students with up to 2 years of data beyond the end of the intervention.

Using routinely collected data for the entire target population, we failed to confirm earlier findings of an intervention effect observed in a subset of students in grades 5-7. Volunteer bias in the prior evaluation and/or measurement error in the routinely collected data are potential reasons for the discrepant findings.