Randomized controlled trials of self-monitoring interventions with or without incentives for diet and exercise among individuals with overweight or obesity: Psychological and behavioural effects.

Objectives: To test the effects of three behavioural interventions (daily monetary incentives + self-monitoring, delayed lump sum monetary incentives + self-monitoring, and self-monitoring only) on psychological constructs and fruit and vegetable consumption or physical activity behaviour change among a sample of adults with overweight or obesity.

Design: A pair of 3-arm longitudinal randomized controlled trials compared daily monetary incentives + self-monitoring, delayed lump sum monetary incentives + self-monitoring, and self-monitoring only interventions for either fruit and vegetable consumption or physical activity.

Methods: Individuals reporting elevated weight status and insufficient engagement in one of the target behaviours were randomly assigned to one of three 3-week interventions. All three interventions involved daily self-monitoring of the behaviour, and two provided monetary incentives contingent upon reported behaviour. Participants completed measures of psychological constructs and reported behaviour at baseline, the end of the intervention, and two and four weeks post-intervention.

Results: Participants across all three intervention conditions demonstrated increased engagement in the target behaviour from pre- to post-intervention and reported behaviour remained above baseline levels at both follow-up time points. Increases in reported behaviour during the intervention were associated with increases in self-efficacy, and this enhanced self-efficacy prospectively predicted sustained reported behaviour at follow-up. However, contrary to hypotheses, the incentive interventions including self-monitoring were not more efficacious than self-monitoring alone, and increased reported behaviour was not associated with enhancements in attitudes.

Conclusions: Self-monitoring interventions can aid behaviour change efforts, and behavioural practice during these interventions can increase self-efficacy. However, among adults with overweight or obesity who are seeking behaviour change interventions, incentive-based self-monitoring approaches may not be superior to self-monitoring alone in driving behaviour change and maintenance.