Changes in Teenagers’ Dietary Choices in Smart School Canteens: A Pre-Post Single-Arm (Quasi-Experimental) Study of a Digital Nudge Intervention

<b>Background/Objectives</b>: Adequate adolescent nutrition is vital for lifelong health, yet traditional school meal programs often emphasize processed foods. Digital nudges, subtle digital changes, may help promote healthier food choices. This study aimed to evaluate the impact of a digital nudge intervention in a smart school canteen on students' food choices and nutrient intake over three months. <b>Methods</b>: A pre-post single-arm (quasi-experimental) study was conducted among 502 high school students (aged 15-17) in Shenyang, China. In August 2023, the school implemented a smart canteen with a mobile mini-program for meal pre-ordering. Embedded digital nudges included improved visibility of healthy options, nutritional information, and default settings favoring nutritious choices. Dietary intake was assessed using a 3-day 24 h dietary record and a food frequency questionnaire. Paired <i>t</i>-tests, Wilcoxon signed-rank, and chi-square tests were used for analysis. <b>Results</b>: Post-intervention, the weekly consumption frequency of coarse grains (<i>p</i> = 0.017), fruits (<i>p</i> < 0.001), seafood (<i>p</i> < 0.001), and soy products (<i>p</i> < 0.001) significantly increased, while sweets (<i>p</i> = 0.033), sugary drinks (<i>p</i> = 0.015), fast food, and eating out (both <i>p</i> < 0.001) decreased. Daily calcium intake rose from 683.00 mg to 804.11 mg (<i>p</i> < 0.1), and the proportion meeting recommendations increased from 39.3% to 50.9%. No significant change was observed in vitamin C intake (<i>p</i> = 0.192). <b>Conclusions:</b> The digital nudge intervention in the smart school canteen effectively improved students' dietary choices, particularly increasing the consumption frequency of healthy foods and dietary calcium intake.