Adherence to the Planetary Health Diet and Its Association with Diet Quality and Environmental Outcomes in Croatian University Students: A Cross-Sectional Study

Background/Objectives: University students are at a critical life stage for establishing lifelong dietary habits, yet little is known about the sustainability of their diets, especially in Croatia. This study aimed to assess the sustainability and environmental impact of university students' dietary patterns at the University of Rijeka using the Planetary Health Diet Index (PHDI), and to explore associations with demographic, lifestyle, nutritional, and environmental variables. Methods: A cross-sectional study was conducted from October 2023 to March 2024 among 224 students (54% male, mean age 22.7 ± 2.2 years). Data collection included sociodemographic information, physical activity, and dietary intake (semi-quantitative FFQ). Diet quality was assessed using the PHDI, Mediterranean Diet Score (MDS), and Dietary Inflammatory Index. Environmental impact indicators (carbon, water, and ecological footprints) were calculated using energy-adjusted intake data and standardized life cycle assessment data. Results: Students exhibited moderate adherence to the Planetary Health Diet (mean PHDI: 55.5). Higher PHDI scores were significantly associated with vigorous physical activity, higher MDS, and anti-inflammatory dietary patterns (all p<0.001). Despite male students showing slightly higher PHDI scores, their diets had significantly greater environmental impacts. A one-point increase in PHDI correlated with lower environmental footprints (carbon: β=–7.94; water: β=–13.88; ecological: β=–3.15; all p<0.001). Nutrient and food group analysis supported the health-promoting profile of diets aligned with the PHDI. Conclusions: This study highlights moderate sustainability of students’ diets, with significant associations between diet quality and environmental impact. University settings present key opportunities for promoting sustainable, health-oriented eating behaviors among young adults.