Design and evaluation of the "Feel Good" feasibility study - a multi-component fruit and vegetable intervention in children measuring cognitive and mental health outcomes.

Background: Observational evidence suggests that increasing fruit and vegetable (FV) intake has the potential to improve children's cognitive function and mental well-being, but this has not yet been empirically tested in intervention research. This study assessed the feasibility and acceptability of a multi-component FV intervention which measures mental and cognitive health outcomes in children.

Methods: The 'Feel Good Study' was a cluster-randomised controlled feasibility study conducted in four New Zealand primary schools, with equal allocation of schools to intervention and wait-list control arms. The intervention group received a 10-week FV programme informed by behavioural theory, including school- and home-based components designed to improve FV availability and acceptance. The wait-list control group received a simplified 5-week version of the intervention. Dietary, cognitive, and mental health outcomes were completed by children and parents/caregivers at the start and end of the 10-week study period. Primary outcomes of this feasibility study were recruitment, retention, and data collection rates. Process evaluation captured measures of intervention fidelity and dose, acceptability, reach, and barriers or facilitators to implementation.

Results: Seventy children were recruited (79% of target recruitment rate), with an average retention rate of 89%. Diet, cognitive, and mental health data collection procedures were feasible, with all data valid for analysis except for 6% of children's dietary questionnaires. All intervention components were delivered (100% dose delivered), with high levels of fidelity (82% - 100% of components implemented as planned). All teachers and parents strongly agreed that they would recommend other schools/families take part in the study, indicating high levels of acceptability. Process evaluation revealed areas for refinement including more cohesive connections between school- and home-based intervention components, strengthening or adding new intervention components, and simplifying enrolment procedures with longer recruitment periods.

Conclusion: Having satisfied key feasibility and acceptance measures in the Feel Good Study, we recommend intervention refinement and progression to a definitive trial where the efficacy of increased FV intake for mental health and cognitive function can be tested in children for the first time.

Trial registration: The trial protocol was prospectively registered with the Australia and New Zealand Clinical Trials Registry (ACTRN12623000533695) on 2 May 2023, https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=385829&isReview=true .