RESUMO
OBJECTIVES: Adolescents tend to overestimate the extent of peers' unhealthy snacking consumption and such misperceptions have been associated with increased personal unhealthy snacking. This study aims to test whether a Social Norms Approach (SNA) intervention which challenges these misperceptions of peers' unhealthy snacking will have a positive effect on students' personal unhealthy snacking behaviours, related attitudes, and behavioural intentions. DESIGN: A quasi-experimental study tested the effectiveness of an in-school SNA intervention (n = 163) compared to a control condition (n = 95) among 11-12-year-old students. METHOD: Both conditions received healthy eating information, while students in the SNA intervention received additional normative feedback (outlining the discrepancies between perceived and actual unhealthy snacking of the majority based on baseline data) delivered through an interactive poster-making session. Students completed self-reported measures of personal unhealthy snacking, related-attitudes, behavioural intentions, and normative perceptions (descriptive and injunctive) at baseline, post-intervention, and at a 3-month follow-up. RESULTS: Students who received SNA feedback were significantly less likely to overestimate peers' unhealthy snacking attitudes post-intervention (F(1,232) = 16.405, p < .001), and at 3-month follow-up consumed fewer unhealthy snacks (F(1,232) = 6.133, p = .014) and had less positive attitudes towards unhealthy snacking (F(1,198) = 8.779, p = .003). The changes in personal snacking attitudes at 3-month follow-up were mediated by changes in normative misperceptions about peers' unhealthy snacking attitudes post-intervention, which indicated that the reductions in normative misperceptions following SNA messages mediated the effect of the intervention. CONCLUSION: The results indicate that in-school SNA interventions which challenge normative misperceptions constitute a promising strategy for reducing unhealthy snacking in young adolescents.