Validation of the most cost-effective nudge to promote workers’ regular self-weighing: a cluster randomized controlled trial

Regular self-weighing is useful in obesity prevention. The impact of nudge-based occupational self-weighing programs in the cluster randomized controlled trial was examined. The primary outcome was regular self-weighing after 6 months, which we used to compute cost-effectiveness. Participants were Japanese local government employees who underwent 1 h workshops after being assigned to one of the three nudge groups. Each group was designed according to the nudges’ Easy, Attractive, Social, Timely framework: quiz group (n = 26, attractive-type nudges), implementation intentions group (n = 25, social-type nudges), and growth mindset group (n = 25, timely type nudges). A reference group (n = 36, no nudges) was also formed. After 6 months, all three interventions were effective for regular self-weighing, with the growth mindset intervention (60.0%) being significantly more effective. The cost-effectiveness of the growth mindset group was 1.7 times and 1.3 times higher than that of the quiz group and the implementation intentions group, respectively. Findings from our study are expected to facilitate the use of nudges for health practitioners and employers, which in turn may promote obesity prevention.