Efficacy of health behaviour interventions using the health action process approach: a systematic review and...

The Health Action Process Approach (HAPA) is a prominent social-cognition model of health behaviour change, but its efficacy across diverse domains and populations requires systematic evaluation. This systematic review and meta-analysis evaluated the overall efficacy of HAPA-based interventions and examined potential moderators. Eligible studies were randomized controlled trials that explicitly nominated the HAPA as an intervention basis and assessed at least one health behavior outcome. Five electronic databases were searched from inception to February 2025, identifying 74 randomised controlled trials (197 effect sizes) comprising 9,115 intervention and 8,858 control participants. A random-effects multilevel meta-analysis revealed a significant overall post-intervention effect on health behaviours (d = 0.459). Significant effects emerged for physical activity (d = 0.504), fruit and vegetable consumption (d = 0.636), and other dietary behaviours (d = 0.776). Subgroup analyses identified several key moderators: interventions targeting approach behaviours yielded significant effects (d = 0.497), whereas those targeting avoidance behaviours were non-significant. Dual-phase interventions targeting both motivational and volitional constructs (d = 0.532) outperformed volitional-only (d = 0.350) or motivational-only (d = 0.289) designs. Furthermore, larger effect sizes were observed for interventions using inactive control groups (d = 0.543), delivered to clinical populations (d = 0.559), employing hybrid delivery modes (d = 0.672), and lasting 12-24 weeks (d = 0.619). These findings demonstrate that HAPA-based interventions are effective, particularly when utilising dual-phase, hybrid, and longer-term designs for clinical groups. Future research should focus on optimising intervention design and elucidating mechanisms underlying sustained behaviour change.