The power of descriptive social norms at lunch time: when behaviour becomes contagious

BACKGROUND. Descriptive social norms, which indicate what most people do, are increasingly being used to nudge healthier choices. However, evidence of their effectiveness is mixed in adults, and their application to guide food choices is recent. This study evaluates the effectiveness of a descriptive social norm intervention in increasing healthy food choices among users in three hospital canteens in the Friuli Venezia Giulia region (Italy). METHODS. For two months, descriptive social norms regarding fruit choice (instead of dessert) and vegetables (at least one portion), were posted in three hospital canteens (C1, C2 and C3), then removed just before data collection. Users’ trays were photographed at their first access during 5 working days between August and September 2023. A questionnaire was distributed to collect users’ characteristics and assess correct recall of the messages. Multiple logistic regression (alpha < 0.05) was performed to examine the association between each message and the corresponding choice, adjusted for sex, age group, typology of work (shift/non-shift). RESULTS. 1,624 user questionnaires and trays were analyzed (1,005 from C1, 348 from C2, 271 from C3). The total sample included 899 females and 725 males; the median age was 45 years. 83% of those who correctly recalled the fruit message chose fruit (vs. 74% of those who did not). 83% of those who recalled the vegetable message chose at least one portion (vs. 73% who did not). A significant association emerged with users who remembered the message being more likely to choose fruit (OR: 1.91 [1.21-3.04]), and vegetables (OR: 1.90 [1.29-2.81]). CONCLUSIONS. Descriptive social norms showed positive effects on fruit and vegetable intake, suggesting their potential as a tool for promoting healthier food choices in hospital canteens and their possible scalability to all workplace canteens.