The times that we choose to go to bed and wake up are rarely fixed. As with any behavior, sleep timing is variable and influenced by a host of biological and environmental factors. Presumably, the circadian system and sleep homeostat evolved to cope with day-to-day changes in sleep timing within a certain range, beyond which maladaptive responses occur. For example, in shift workers there is often a large mismatch between their daily activity patterns (e.g., sleeping and eating) and the timing of their circadian system. This misalignment contributes to sleep disturbances and is associated with impaired glucose tolerance.1,2 Epidemiological studies have shown that chronic exposure to shift work is associated with increased risk of obesity, metabolic syndrome, and type 2 diabetes.3,4 These findings suggest that keeping a highly irregular sleep-wake schedule contributes to poor metabolic health.