One-year post-intervention effectiveness of a proportionate universal intervention in reducing social inequalities of weight status among adolescents.

Introduction: The effectiveness of interventions in reducing social inequalities of weight status among adolescents is challenging. Studies reporting post-intervention effectiveness are scarce. We aimed to evaluate the 1-year post-intervention effectiveness of PRALIMAP-INÈS (PRomotion de l'ALIMentation et de l'Activité Physique - INÉgalité de Santé) trial.

Methods: Participants of the PRALIMAP-INÈS trial, a proportionate universal intervention of 1-year in 11-13 years-old children recruited in 35 schools of Nord-Est France which compared socially advantaged to less advantaged children, who had completed data at 1-year (T1) and 2-year follow-up visit (T2=1-year post-intervention) were included. The first group received a standard lifestyle intervention (advantaged with standard care [A.S]) and the second a reinforced lifestyle intervention (less advantaged with standard and strengthened care [LA.S.S]). This proportionate intervention led to similar benefit in the two groups after 1-year of intervention. The present work looked at the retention effect of this proportionate intervention 1-year after the end of the lifestyle program. The main outcome was the change in body mass index z-score (BMIz) from T1 to T2. Between-group outcomes changes analysis involved the t test for equivalence using a Two One-Side Test procedure and hierarchical mixed models. Multiple imputation was performed to handle missing data.

Results: This study included 505 adolescents (338 in A.S and 167 in LA.S.S groups) of mean age: 15.2±0.7 years. The equivalence was evidenced for BMIz (0.01[90% confidence interval, -0.05 to 0.07]), BMI (0.02[-0.26 to 0.29]), BMI percent of the 95th percentile of Centers for Disease Control and Prevention (CDC) growth chart reference (0.01[-0.94 to 0.96]), BMI minus 95th Percentile of CDC growth chart reference (0.01[-0.26 to 0.29]) and proportion of obesity (-0.01[-0.04 to 0.04]) from T1 to T2 between LA.S.S and A.S. Nevertheless, we did not show significant difference between the two groups for nutrition behaviors outcomes at 1-year post-intervention.

Conclusion: At 1-year post-intervention, we showed equivalence in adolescents' weight status changes whatever the socioeconomic class. Therefore, this proportionate universal intervention applied to adolescents in a school setting seems effective to prevent the worsening of the social inequalities of weight status in response to a lifestyle intervention at 1-year.