Figure 1.

Example Study Protocol. A 16 day study protocol for a participant with a habitual sleep schedule of 24:00−08:00. The 8 h self-selected sleep schedules maintained at home are represented by black bars on days 1−7 and 9−15. During days 6−8 and 14−16, participants were provided an energy-balanced diet. Participants arrived at the laboratory on the evening of the 8th and 15th days of the study and were maintained in dim light for the study visit during scheduled wakefulness (represented by the gray bars) and darkness during scheduled sleep (represented by black bars). Participants were assigned first to either an 8 h sleep opportunity at their habitual time as a control condition or a 6.5 h sleep opportunity that began 1 h prior to habitual bedtime and ended 2.5 h prior to habitual wake time as a simulated early morning shiftwork condition. For each visit, participants completed baseline metabolic testing and blood samples were taken for metabolic and circadian markers after scheduled wake time. Participants were served an identical breakfast ~45 min after waking in each condition (represented by “B”) and post-meal testing continued for ~3 h.