Evaluation of self-weighing promotion interventions integrating health education with transparent priming and commitment nudges: A one-year randomized controlled trial

Self-weighing can be effective in obesity prevention; however, many individuals tend to procrastinate in adopting this behavior. Nudges can address this procrastination; however, concerns about their long-term durability and their effectiveness under conditions of transparency continue to impede their implementation. This study aimed to evaluate the one-year effects of a self-weighing promotion workshop incorporating disclosed nudges and health education through a randomized controlled trial. In September 2019, participants in a Japanese community-based workshop were assigned to either a negative-priming group or a positive-priming group. At the beginning, priming nudge-based interventions were implemented: the negative-priming group completed quizzes highlighting the disadvantages of obesity, whereas the positive-priming group shared success experiences and received positive feedback. Subsequently, all participants received the same health education and were asked to declare specific self-weighing plans, incorporating a commitment nudge. The modified intention-to-treat analysis was conducted among 62 and 51 participants in the negative-priming and positive-priming groups, respectively. Within-group comparisons showed that both groups had a significant increase in weekly self-weighing frequency after one year; by 1.06 measurements in the negative-priming group (p < 0.001, Cohen's d = 0.44) and by 1.17 measurements in the positive-priming group (p < 0.001, Cohen's d = 0.52). No significant differences were observed between the groups. The effect sizes observed in this study appear to be comparable to or larger than those reported in previous studies, even after one year. These findings suggest that combining health education with transparently disclosed nudges may support self-weighing over one year. • This study is one of the few examining the impact of transparent non-default nudges. • Concerns about nudges' durability and transparency may hinder their wide adoption. • Transparent priming and commitment nudges sustained self-weighing for one year. • Positive effects persisted despite COVID-19 constraints. • The study has practical implications for public health and behavioral economics.