Health messages to promote fruit and vegetable consumption at different stages: A match-mismatch design

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.