Associations of Temporal Eating Patterns with Nutrient Intake Variability and Diet Quality Among Japanese Female Mobile Application Users

<b>Background/Objectives:</b> Although lifestyle patterns, including sleep and meal timing, have been associated with diet quality, previous studies have frequently relied on time-averaged data, which can obscure day-to-day intake variability. Using data from a food-logging mobile application, we aimed to elucidate the association between mealtime irregularity and nutrient intake variability. Furthermore, we explored whether the association between meal timing and diet quality differs depending on mealtime regularity. <b>Methods:</b> Chrononutritional characteristics were calculated for 742 female mobile application users who provided daily dietary records for approximately 1 month. Nutrient intake variability was evaluated using the coefficient of variation (CV). Diet quality was assessed based on the energy-adjusted ratio of nutrient intake to the reference values from the Dietary Reference Intakes for Japanese. Generalized additive models adjusted for age, body mass index, and physical activity were employed for analyzing associations. <b>Results:</b> Greater mealtime irregularity was associated with higher CVs in the daily intake of most nutrients investigated. Regarding diet quality, a marginal interaction was observed between mealtime regularity and dinner timing (<i>p</i> for interaction = 0.062). Specifically, the irregular mealtime group demonstrated a significant linear decline in diet quality with later dinner times (<i>p</i> for trend = 0.0112), whereas no significant decline was observed in the regular mealtime group (<i>p</i> for trend = 0.5219). <b>Conclusions:</b> Our findings suggest that mealtime regularity, alongside meal timing, is a significant factor involved in nutrient intake variability and diet quality, underscoring its significance as a health-related behavior in chrononutrition.