Monetary Incentive Interventions Can Enhance Psychological Factors Related to Fruit and Vegetable Consumption

Incentive interventions have gained popularity to motivate health behavior change, but some psychological theorists caution that they may have deleterious effects on factors that potentiate behavior maintenance. Importantly, no empirical study has tested whether incentives indeed have iatrogenic effects on key psychological constructs associated with health behavior change and maintenance. The study aims to explore the effects of monetary incentives on theoretically informed psychological constructs and fruit and vegetable consumption. Individuals reporting insufficient fruit and vegetable consumption were randomly assigned to receive either daily monetary incentives, delayed monetary incentives, or no incentives for their fruit and vegetable consumption during a 3-week intervention period. Behavior engagement and psychological factors were measured at baseline, at the end of the intervention, and 2 weeks following the cessation of the intervention. Participants in the daily incentive condition demonstrated the greatest increase in self-reported consumption during the intervention and at the follow-up. Moreover, increases in consumption during the intervention period were associated with increases in attitudes and self-efficacy, which, in turn, predicted behavior maintenance at follow-up. Intrinsic motivation to consume fruits and vegetables increased over time across the entire sample but did not differ between groups. Monetary incentives can alter health behavior engagement without decreasing intrinsic motivation or other relevant cognitive and motivational constructs. Further, although incentives may serve as a vehicle to initiate behavior change, increased experience with the behavior may then lead to enhancements in key psychological constructs that serve as mechanisms to potentiate behavior maintenance following the cessation of incentives. The trial was registered with the ClinicalTrials.gov database (NCT02594319).