Free ghrelin and leptin response to a meal in young and older participants at baseline, following an average of 19 days of prolonged sleep restriction combined with circadian disruption, and following 9 days of stable re-entrainment and recovery sleep. In young (panels A, C, E, G) and older subjects (panels B, D, F, H), mean profiles (± 95% C.I) are depicted for free ghrelin (panels A-D) and leptin per percent body fat (panels E-H) and aligned relative to an identical, standardized breakfast (time=0) under conditions of baseline sleep replete (≥10 h TIB/24 h [dashed black line]), history of prolonged sleep restriction combined with circadian disruption (5.6 h TIB/24 h [solid red line]), and following 9 days of stable circadian re-entrainment and recovery sleep (10 h TIB/24 h [solid grey line]). In each condition, breakfast was served at the same circadian temperature phase ± 4 h (0.7 h ± 1.8 h). Sleep periods are depicted by horizontal bars, meals by vertical bars.