Applying the Social Norms Approach to reduce unhealthy dietary behaviours amongst secondary school students.

Adolescence is a period of rapid growth, and optimal nutrition during this period is essential for healthy development. Adolescents tend to align their dietary behaviours with the perceived normative dietary behaviours of their peers; however, these normative perceptions are not always accurate with adolescents tending to overestimate the extent of peers’ unhealthy dietary practices which can lead to personal unhealthy dietary practices. The Social Norms Approach (SNA) operates on the premise that challenging these misperceptions should decrease the social pressure to engage in the behaviour, leading to a reduction in the behaviour.

This thesis aims to examine whether an in-school SNA intervention could reduce the unhealthy dietary behaviours of secondary school students. Study One used focus groups to explore the perceived influences of healthy and unhealthy food choices amongst students. The systematic review presents a review of the literature focused on school-based interventions which have been designed to improve dietary behaviours of adolescents. The findings from Study One together with results from both the systematic review and a narrative review, and input from key stakeholders, informed the design of the in-school SNA intervention. Study Two tested for the existence of unhealthy snacking-related misperceptions amongst students and whether these misperceptions are associated with personal unhealthy snacking behaviour. Study Three tested the ability of the SNA intervention to challenge commonly held normative misperceptions as a means of reducing unhealthy snacking amongst students. Finally, Study Four qualitatively explored students' and teachers’ experiences of the intervention.

Study One indicated that although students had a good understanding of healthy dietary behaviours, they would often skip meals and consume unhealthy snacks. Study Two found that normative misperceptions predicted young adolescents’ unhealthy snacking consumption, and Study Three demonstrated that the in-school SNA feedback intervention was an effective strategy for reducing personal unhealthy snacking behaviours amongst 11- to 12-year-olds. Study Four found that the intervention was an age-appropriate engaging method for delivering SNA feedback to young adolescents, but these students needed to be afforded more time to process, discuss and understand the SNA feedback being communicated. The findings of this thesis indicate that SNA interventions can be applied successfully within a school setting to reduce unhealthy snacking of younger adolescents.