[Providing nutritionally balanced meals and examining the factors associated with choice: An intervention study using nudges in a local restaurant].

Abstract

Objectives　This study implemented nutritionally balanced meals (T-set meals) at a local restaurant, and nudged selection of those meals, to evaluate the changes in menu usage and clarify the reasons for customers' meal choices.Methods　This pre-post intervention study was conducted at the T Restaurant in Toda City over 8 weeks (September-October 2024). The interventions included: (1) provision of T-set meals based on the Smart Meal^® criteria (two types of meals offered over two 4-week phases); (2) information provision using menu displays. Weeks 1-2 and 5-6 constituted Intervention Period A, during which menus displayed only meal names and prices. Weeks 3-4 and 7-8 comprised Intervention Period B, during which photographs and menu details were added. Development of the T-set meals and menu displays was based on the CAN nudge framework (C = Convenient, A = Attractive, N = Normative). The primary outcome was a change in the number and composition ratio of meals sold by category, evaluated by (1) changes in the outcome in the month before and after the intervention; (2) comparing Intervention Periods A and B. To examine the reasons for selecting T-set meals, online surveys were conducted during weeks 5 and 7. Only first-time respondents were included in that analysis. The characteristics of respondents and reasons for their selection were compared. In a sub-analysis, the reasons for selecting T-set meals were compared between for week 5 (Period A) and week 7 (Period B).Results　During weeks 1-4, the composition ratio of all menu (except T-set meals) categories significantly decreased compared with the pre-intervention period. However, in weeks 5-8, the proportion of grand menu items (set meal) increased again, returning to the pre-intervention level (27.6% vs. 30.6%). The proportion of T-set meals significantly increased during Period B in weeks 1-4 but significantly decreased during Period B in weeks 5-8. During intervention Period B, more number of respondents cited reasons such as "collaboration with Kagawa Nutrition University," "contains a lot of vegetables," "looks tasty," and "affordable price" for selecting the T-set meals.Conclusion　These findings suggest that menu displays incorporating nudges, particularly those emphasizing visual appeal and pricing advantages, can positively influence meal selection. However, when a dish is unfamiliar or does not align with customer preferences, informational nudges alone may be insufficient to drive choice.