0043 Circadian Rhythm of Energy Expenditure and Substrate Utilization During Constant Routine Conditions

Introduction Findings from previous studies indicate daily variation in energy expenditure (EE) depends on circadian phase in humans, though findings have been inconsistent. Changes in energy expenditure throughout the day and night during non-fasting conditions are important to understand factors influencing energy metabolism. The aim of this study was to determine the circadian rhythm of resting EE, respiratory quotient (RQ), and substrate utilization using a constant routine protocol. Methods Six healthy adults (3F, age 27.7±2.2 years, BMI 24.7±3.2; mean±SD) participated in a 26-hour constant routine study following 1 week of outpatient monitoring. Subjects arrived at the laboratory in the evening and were provided an 8-hour sleep opportunity. After waking at their habitual time, participants remained in constant conditions, which included dim light (