Adherence to healthy and sustainable diets and health-related behaviors in a Spanish online university setting

Background Universities represent strategic environments for promoting healthy behaviors. Evaluating dietary quality and sustainability alongside other health-related factors is essential for developing health promotion strategies. Objective This study aimed to assess adherence to diets based on the latest Spanish healthy and sustainable dietary guidelines, and to explore associations between diet, health-related behaviors, and sociodemographic characteristics among students and staff at the Open University of Catalonia (UOC). Methods An online cross-sectional survey was conducted during the 2020–2021 academic year ( n = 2,608; 2,075 students, 533 staff). Data on food intake (via a semi-quantitative food frequency questionnaire), physical activity (PA), sedentary behavior (SB), sleep quality, and emotional well-being were collected. HEAlthy and SUStainable diet index (HEASUS) was computed using a continuous gradient-based scoring system for 18 food groups, ranging from −1 (lowest adherence) to 10 (highest adherence). Quantile regression models were employed to examine determinants of HEASUS adherence across tertiles, accounting for health-related and sociodemographic covariates. Results Overall, many participants exhibited low PA, insufficient sleep, and elevated stress. Adherence to healthy and sustainable diet according to HEASUS was moderate (students: 5.9 ± 1.5; staff: 6.2 ± 1.4). Higher PA and active commuting were positively associated with HEASUS, while SB, male gender, and overweight status were inversely associated. Health-related factors showed stronger associations with HEASUS adherence at lower quantiles, indicating that unhealthy behaviors cluster and reinforce each other more strongly among those with poorer dietary adherence. Although females scored slightly higher on HEASUS, they reported greater stress, poorer sleep, and higher SB. Conclusion Our findings underscore the importance of integrated, gender-sensitive strategies that jointly address diet quality, PA, sleep, and emotional well-being. Online universities represent an important setting for promoting both health and sustainability, especially through targeted actions that support a plant-rich, nutrient-dense dietary pattern, enhance emotional well-being, and encourage more active daily routines.