Evaluating the mechanisms of action and participant experiences of a web-based, evolutionary mismatch-framed intervention targeting physical activity and diet.

Background
This study sought to understand the mechanisms through which a novel web-based intervention for adults with overweight/obesity brought about change in physical activity and dietary behaviours. The intervention used a rationale based on the evolutionary mismatch hypothesis and aimed to support behaviour change through the inclusion of self-regulatory techniques delivered in an autonomy supportive climate.
Methods
Men and women aged 35-74 years with a body mass index of 25-39kg/m2 were eligible. Fifty-nine participants were randomised to receive the intervention (n=30) or standard NHS resources (control). The 12-week intervention consisted of a website hosting behaviour change techniques, pedometers and dietary feedback. Physical activity level (PAL), energy intake (EI) and anticipated mediators of change – autonomous motivation, self-efficacy, self-regulation, habit and social support – were assessed at baseline and post intervention. Semi-structured interviews were conducted with intervention group to explore their experience with the intervention.
Results
Differences between groups’ PAL and EI change scores were of small to medium effect size but was not statistically significant (d=0.32 and d=-0.49, respectively). The intervention led to small but meaningful increases in autonomous motivation and self-efficacy, and these were associated, as predicted, with large increases in self-regulatory behaviours. Regression-based mediation analysis found action planning to be a significant mediator for the intervention’s impact on physical activity. Other anticipated mediating relationships (involving self-monitoring, coping planning, social support and habit) for physical activity and diet were not supported by the process analysis results. Participants reported finding the intervention acceptable and the mismatch concept interesting; setting weekly goals and plans was reported as the most helpful aspect of the intervention.
Conclusion and implications
Within this sample, action planning was the only mediator to explain changes in behaviour, lending support to the evidence base for including goal setting and planning in physical activity and dietary behaviour change interventions.