Is Better Diet Quality Linked to Better Competitive Functioning? An Integrative Multi-Analytic Study of Sleep Difficulty and Subjective Vitality Among Chinese Collegiate Athletes

Background: Diet quality may be associated with recovery-related experiences and self-reported physical and psychological functioning in athletes. However, the roles of sleep difficulty and subjective vitality in these associations, together with their item-level network structure and predictive relevance, have not been examined within an integrated analytical framework. This study investigated the associations of diet quality with self-rated physical fitness and competitive psychological readiness among collegiate athletes and examined cross-sectional indirect associations involving sleep difficulty and subjective vitality. Methods: A cross-sectional survey was conducted among 1641 collegiate athletes participating in provincial-level university sporting events in Yunnan and Guizhou, China. Assessments were completed on the athletes’ competition check-in day. All core variables were assessed using self-report instruments, including diet quality, sleep difficulty, subjective vitality, self-rated physical fitness, and competitive psychological readiness, with the latter operationalized using mental toughness. Cross-sectional indirect associations were estimated using PROCESS Model 6. Regularized partial-correlation networks and bridge centrality analyses were used to characterize item-level conditional associations. Ridge regression and XGBoost were further applied to evaluate out-of-sample predictive performance, and SHAP values were used to quantify the relative predictive contribution of variables within the XGBoost models. Results: Higher diet quality was significantly associated with fewer sleep difficulties and with higher subjective vitality, self-rated physical fitness, and competitive psychological readiness. Significant indirect associations were observed involving sleep difficulty alone, subjective vitality alone, and the ordered sleep difficulty–subjective vitality term in both outcome models; the subjective-vitality-only estimate was the largest. Network analysis indicated that sleep-difficulty nodes were predominantly characterized by negative bridging connections, whereas subjective-vitality nodes showed primarily positive bridging connections across communities. In the predictive analyses, Ridge regression achieved holdout R2 values of 0.415 for self-rated physical fitness and 0.341 for competitive psychological readiness. In exploratory XGBoost analyses, subjective vitality showed the highest relative SHAP importance in both models. Conclusions: Diet quality was associated with self-rated physical fitness and competitive psychological readiness, operationalized using mental toughness, with additional indirect associations involving sleep difficulty and subjective vitality. These findings provide a conceptual basis for considering nutrition, sleep, and daytime vitality within an integrated athlete-support framework. Their temporal ordering and the effects of modifying these factors require longitudinal and experimental testing.