Objective: To examine the effectiveness of matching health messages promoting fruit and vegetable intake to the Health Action Process Approach stages of change.Design: In a randomised controlled trial, 205 undergraduate students (non-intenders n=123; intenders n=82) were exposed to one of three health messages, targeted at non-intenders, intenders and controls.Main outcome measures: Three longitudinal assessments of stage, fruit and vegetable intake, and social-cognitive determinants were obtained.Results: Stage-specific effects of the interventions were confirmed. For self-efficacy, a stage by health message crossover interaction emerged, with both non-intenders and intenders in the matched conditions scoring higher in self-efficacy. Furthermore, in line with predictions, non-intenders in the matched condition showed higher risk perception, outcome expectancies, intention, and stage progression immediately after message exposure, and lower levels of action planning and coping planning a week later in the mismatched condition, but for these outcomes no differences across conditions were obtained among intenders. Multiple mediation analyses confirmed the facilitating role of self-efficacy and behavioural intention among non-intenders.Conclusions: Stages should be considered when designing health messages, although more interactive interventions for intenders and extended measurement time frames may be required.

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Fruit and vegetable intake,Health message targeting,Stages of change,Randomised controlled trial,Multiple mediation analyses

• Psychology - Social Sciences