Fig. 2.

(A) Experimental protocol included three baseline nights of 8 h in bed (white bars), followed by six night of sleep restriction (4 h in bed; black bars), ending with a seven night period of sleep extension (12 h in bed; light gray bars). The last 2 d of the sleep-debt and sleep-extension periods included identical meals for breakfast, lunch, and dinner (small arrows), an ivGTT to assess glucose metabolism (large arrow), and 24-h blood sampling to examine circulating hormonal profiles (dashed lines). (B) In a randomized cross-over design, two nights of either bedtime extension (10 h in bed; dark gray bars) or sleep restriction (4 h in bed; black bars) were followed by 12 h of blood sampling, coupled with a constant glucose infusion and hourly questionnaires regarding hunger/appetite, mood, and sleepiness. (C) In a randomized cross-over design, two nights of normal sleep (8 h in bed; white bars) or three nights of slow-wave sleep suppression (hatched bars) were followed by an ivGTT (arrow) to assess glucose metabolism.