Self-Reported Chronotype and Diet Quality in Chinese Adolescents: Insights from a Cross-Sectional Study in Xiamen

Background: External constraints can disrupt adolescents’ circadian rhythms, potentially increasing their risk of obesity and metabolic diseases. Methods: This cross-sectional study examined the association between chronotype and dietary quality among 982 adolescents recruited through stratified random sampling in Xiamen, China. Chronotype and dietary quality were assessed using the Morningness–Eveningness Questionnaire (MEQ-19) and the Diet Quality Questionnaire (DQQ), respectively. Results: Univariate analysis indicated that Global Diet Recommendations (GDR) scores, the index of DQQ, varied significantly across grades, BMI and chronotypes (p < 0.05). Multiple linear regression revealed a positive association between MEQ score and GDR-Total (p < 0.001), which appeared to be primarily related to GDR-Health rather than GDR-Limit. Sensitivity analyses confirmed the robustness of these associations when MEQ was treated as either a continuous or categorical variable. Exploratory restricted cubic spline analyses suggested an apparent inverted-U-shaped association between MEQ score and GDR-Total, although its shape was sensitive to knot specification and the inclusion of observations at the distributional tails. GDR-Health showed a predominantly increasing pattern, whereas GDR-Limit showed a U-shaped pattern. Conclusions: Thus, dietary quality initially improved as chronotype shifted from eveningness toward morningness but deteriorated at extreme morningness, suggesting an optimal chronotype range for healthy dietary patterns. These findings support personalized interventions for adolescents that combine improved sleep patterns with increased consumption of health-promoting foods, rather than focusing solely on restricting unhealthy foods.