0118 Endogenous Circadian Rhythm In Diet-induced Thermogenesis In Humans. (27th April 2018) - Vujovic, N
Abstract: Introduction: Recent studies suggest that eating during the biological night/habitual rest phase may increase obesity risk, even when caloric intake and physical activity are controlled for. Preliminary data indicate that the circadian timing system can influence energy expenditure (EE) after a meal, i.e. diet-induced thermogenesis (DIT), with lower DIT in the biological evening (during a night shift simulation protocol). Although circadian unmasking protocols using constant routine (CR) have shown rhythms in overall EE, they have not thus far revealed circadian rhythms in DIT due to their high meal frequency (every 2 hours). To address this question, we used a CR protocol with meals spaced 6 hours apart. Methods: Eleven healthy, overweight adults (BMI 28.7 ± 0.7; age 36 ± 2.6; 2 female) maintained strict regular sleep and meal schedules for 2-3weeks outpatient and 6 days inpatient before participating in a metabolic CR assessment. During CR, participants remained awake for 37 hours in dim (~4lux) light, in constant posture, consuming identical test meals every 6 hours. Using the Vmax Encore indirect calorimeter, EE was measured for 15–20 minutes immediately preceding each meal, then again at 30, 90, 150 and 210 minutes after the start of the meal. DIT for each meal was quantified as area under the curve for that set of 5 recordings. Core body temperature (CBT) was used to assess circadian phase during each individual DIT assessment. A cosinor mixed model was applied to normalized DIT data. Results: Our model indicates a significant circadian rhythm in DIT (p=0.0076), with minimum occurring at 330 degrees (2 hours before CBT minimum), elevated plateau at 90–220 degrees, and an amplitude of 2.5% (of CR mean DIT). This protocol did not reveal significant circadian oscillations in 6-hour fasting EE or respiratory quotient. Conclusion: This is the first characterization of an endogenous circadian rhythm in DIT. Our results suggest that the timing of the circadian nadir in DIT may contribute to positive energy balance in those eating during the biological night. Support (If Any): NIH-R01DK099512, Center for Clinical Investigation at Brigham and Women's Hospital.