Background/Objectives: Dietary behaviors among young adults in Japan have become increasingly polarized, highlighting the limitations of traditional knowledge-based health education. Behavioral science-based approaches such as nudging and gamification may offer alternative strategies. This study aimed to develop and examine a Theory of Planned Behavior (TPB)-based path model of healthy dietary choice behavior among young Japanese adults and to examine patterns associated with a star-rating gamification feature embedded in a nutrition management mobile application. Methods: A total of 188 participants aged 18–39 years completed an online survey assessing TPB constructs and normative factors. Participants used either a star-rating or non-rating version of the FoodLog Athl application. Composite-score-based path analysis and conditional process analyses were conducted to examine relational patterns among constructs. Results: Intention and self-efficacy jointly explained 48% of the variance in dietary behavior, with self-efficacy emerging as the strongest predictor. Several moderation patterns were observed, including those of gender, university year, diet app use, awareness of consequences, and ascription of responsibility. Compared with users of the non-rating version, star-rating users were observed to show higher nutrient scores but lower self-efficacy and dietary behavior scores, along with greater awareness of dietary consequences. These post-intervention findings are exploratory. Conclusions: Self-efficacy plays a central role in healthy dietary choice behavior among young adults, and its association with behavior appears to be shaped by perceived consequences and responsibility. By applying a composite-score-based path analysis within an SEM framework, this study clarifies the structural relationships among TPB components in everyday dietary choice behavior among Japanese young adults. Star-rating feedback may enhance reflective awareness and shows potential as a gamified nudging tool but further research is needed to clarify its effects.
Akitsu et al. (Fri,) studied this question.