0039 Sex Differences In The Effects Of Circadian Misalignment On Appetite Hormones And Substrate Utilization

Abstract

Introduction: Shift work is known to cause circadian misalignment and increase the risk for weight gain and obesity. While emerging evidence indicates some characteristics of the human circadian system and energy metabolism to differ between men and women, little is known about whether sex modulates the effects of circadian misalignment on energy homeostasis. Here we explore the sex differences in the effects of circadian misalignment on appetite hormones, energy expenditure, and substrate utilization. Methods: Fourteen healthy young adults (mean age ± SD, 28 ± 9 y; BMI, 25.4 ± 2.6 kg/m2; 8 men) each underwent two highly controlled 8-day laboratory protocols: a circadian alignment protocol and circadian misalignment protocol in a randomized, cross-over design. Participants consumed an isocaloric diet per 24 h. Identical test meals were given 1 h and 13 h following wake time. Indirect calorimetry measurements were assessed for these test meals sessions. Hourly leptin and active ghrelin concentrations were assessed for 24 h on the first and third test day. Results: The effects of circadian misalignment on the 24-h average level of the satiety hormone leptin differed significantly between women and men (P<0.0001), with ∼7% decreased levels in women (P<0.05) and ∼11% increased levels in men (P<0.0001). Consistently, circadian misalignment also increased the hunger hormone ghrelin by ∼8% during wake periods in women (P<0.05), without significant effect in men. While circadian misalignment had no sex-dependent effect on the percentage change in fasting and postprandial energy expenditure, there were significant sex-dependent effects on glucose and lipid oxidation (P<0.05 and P<0.01, respectively), with significantly lower fasting glucose oxidation (P<0.01), and higher fasting and postprandial lipid oxidation (P<0.001 and P<0.01, respectively) in women, and again no significant effects in men. Conclusion: These findings demonstrate that sex modulates the effects of circadian misalignment on energy metabolism, indicating possible sex-specific mechanisms and countermeasures for unwanted weight gain and obesity in male and female shift workers.