Influencing dietary behaviours in adolescents to reduce the risk of obesity
: a mixed methods approach

  • Lauren Devine

Student thesis: Doctoral Thesis


Optimal nutritional intake during adolescence is widely recognised as essential for current and future health, with dietary habits established during this life stage reported to track into adulthood. Additionally, adolescence represents a time of nutritional vulnerability, with many failing to meet current dietary recommendations. Consequently, there is an urgent need to develop effective and sustainable health promotion strategies among this population group to minimize the risk of ill-health and schools are emerging as a promising environment for dietary intervention. Therefore, the aim of this thesis was to design, deliver and evaluate the feasibility and effectiveness of a peer-led, school-based intervention at improving adolescents’ dietary intakes in the canteen setting, using a mixed-methods approach. An extensive review of the literature highlighted the efficacy of delivering dietary interventions within the post-primary school-setting, albeit identified that the most effective strategy is yet to be determined and further research is needed to reach consensus. To provide an insight into adolescents’ dietary habits, secondary data analysis of participants (n=694; aged 10-13 years) from the Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) Belfast Cohort study was used to identify dietary patterns. Principal Component Analysis identified three dietary patterns, namely, ‘processed’, ‘healthy’ and ‘staple’, with a ‘processed’ dietary pattern typically characterized by energy-dense, high-fat and sugar and low-fibre foods associated with an increased risk of obesity development. To understand common barriers to healthful dietary choices, focus groups with adolescents (n=86) and interviews with school staff (n=29) were conducted highlighting a number of components that could be employed in future school-based dietary interventions, namely, placement manipulations, labelling/ menu strategies, rewards and peers. These findings led to the development of a 12-week peer-led (aged 16-17 years), school-based (3 intervention; 1 control) pilot feasibility study which targeted Year 8 pupils (aged 11-12 years) to promote improved dietary choices in the canteen setting. Cashless canteen till systems were used to collect data which showed positive findings at improving the selection of ‘dessert’ items; however, no difference was observed in those categorized as ‘main’ meals, potentially as a result of several limiting factors. Process evaluation of this study demonstrated that the intervention was viewed as feasible and acceptable among participants, further identifying barriers to implementation and solutions for future intervention design. This thesis shows promising findings which warrant further investigation in a larger, more representative fully-powered cluster-randomised controlled trial, taking process evaluation findings into consideration for optimal design.
Date of AwardOct 2023
Original languageEnglish
SponsorsDepartment for the Economy
SupervisorAlison Gallagher (Supervisor) & Alyson Hill (Supervisor)


  • School
  • Post-primary
  • Dietary choices
  • Canteen

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