Fig. 2. The appetite-stimulating hormone ghrelin and the satiety hormones leptin and PYY are affected by energy intake, sleep and circadian rhythm in healthy adults.

The figure shows blood hormonal profiles during adequate sleep with diet controlled for energy balance at baseline as well as the circadian rhythm of these hormones during a constant routine protocol with hourly snacks. During conditions of habitual sleep timing with adequate sleep and an energy-balanced diet, levels of ghrelin peak near the beginning of sleep and decrease across the sleep episode (part a). From a circadian perspective, levels of ghrelin increase across the biological day and decrease across the biological night (part b). During conditions of habitual sleep timing with adequate sleep and an energy-balanced diet, levels of leptin are higher during sleep than during wakefulness, peak near the beginning of sleep and decrease thereafter (parts c), while levels of peptide-YY (PYY) are higher during wakefulness than during sleep (parts e). From a circadian perspective, levels of leptin decrease across the biological night and increase across the biological day; inset shows the percentage change for the circadian variation in leptin (part d). By contrast, levels of PYY increase across the biological night and decrease across the biological day (part f). Graphs show mean data with b-spline creating smooth curve fits. For comparison purposes, data for each hormone are plotted on the same scale. Parts a, c and e: Adequate sleep with diet controlled for energy balance at baseline. Parts b, d and f: circadian rhythm constant routine with hourly snacks. B, breakfast timing; D, dinner timing; L, lunch timing. Data from refs.^76,80.