An interval-based approach to measuring eating jet lag in female healthcare shift workers

Circadian rhythms regulate physiological and metabolic functions, and their disruption, particularly from shift work, is associated with adverse health outcomes such as obesity or cardiovascular disease. Meal timing variability, or eating jet lag, has emerged as a valuable marker of circadian misalignment. This study introduces a novel method to assess eating jet lag through direct comparison of food intake intervals, addressing limitations of traditional midpoint-based approaches reducing intervals to single values, potentially overlooking meaningful overlap. We conducted a cross-sectional study on 290 female healthcare professionals in Asturias, Spain, from a larger cohort of 679 participants with complete temporal data for meals across morning, afternoon, and night shifts. The proposed method calculates the degree of embedding between intake intervals during work shifts and rest days, and a global index is derived by aggregating alignment values across shifts. Results show that the interval-based method captures temporal overlap not represented by the midpoint-based approach, especially where the midpoint method underestimates alignment. Bland-Altman analysis showed systematic and proportional disagreement between the two approaches, with discrepancies greater at lower levels of alignment. This approach provides complementary information for evaluating eating-window alignment and provides a basis for future studies between eating-window alignment and health-related outcomes.