Background: Having a late chronotype, that is, the tendency to go to sleep and wake up at later hours, influences an individual's physical and mental health. Despite a few studies noting the association of chronotype with healthy dietary patterns, this relationship remains unclear. Purpose: This study aimed to describe the association of chronotype with healthful and unhealthful plant-based diet quality in female Japanese undergraduate students. Design: Cross-sectional. Participants and setting: A total of 218 female university students in Tokyo, Japan. Main outcome measures: Healthful and unhealthful plant-based dietary index-Japanese version (hPDI-J and uPDI-J), calculated using the validated brief-type self-administered diet history questionnaire. Statistical analyses performed: A five-model stepwise multiple linear regression analysis was conducted. Independent variables were hPDI-J and uPDI-J scores, and dependent variables were various lifestyle habits related to the circadian rhythm and demographic characteristics. Results: Mean (standard deviation) sleep duration, midpoint of sleep, sleep latency time, and social jetlag were 411 (60) min, 03:56 (00:57), 21 (27) min, and 50 (39) min, respectively. Chronotype and several variables, such as residential status, energy and alcohol intake, and nutritional knowledge, were associated with healthful and unhealthful plant-based diet quality. Individuals who had higher hPDI-J scores were more likely to have an earlier chronotype (β = −0.168, P = 0.019) and better nutritional knowledge (β = 0.164, P = 0.022) than those with lower hPDI-J scores. Individuals were more likely to have higher uPDI-J scores if they were living alone (β = −0.301, P < 0.001), had a later chronotype (β = 0.181, P = 0.001), higher frequency of snacking (β = 0.164, P = 0.019), lower total energy (β = −0.445, P < 0.001), and worse nutritional knowledge (β = −0.172, P = 0.001). Conclusion: This study provided new evidence as to the relationship between sleep and dietary habits, the interaction of which may affect women's health.
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