This pilot clinical trial will test the hypotheses that sleep restriction (for 5 nights), in comparison to "normal sleep", will:

1. Decrease peripheral insulin sensitivity and glucose tolerance, as measured by the hyperinsulinemic-euglycemic clamp and oral glucose tolerance test.
2. Decrease hepatic insulin sensitivity, as assessed by stable isotope studies of endogenous glucose production, gluconeogenesis and glycogenolysis.

Over the past 50 years, the incidence of diabetes has increased dramatically, while sleep duration in the US has decreased significantly. Epidemiological studies and small clinical trials suggest that these trends are causally related. In this study, our goal is to determine the mechanisms by which decreased sleep duration directly affects insulin sensitivity. The investigators will perform a clinical study in 20 healthy volunteers to determine whether 5 nights of sleep restriction decreases insulin sensitivity in the peripheral tissues (ie, skeletal muscle) or liver.

Peripheral insulin sensitivity will be measured by the hyperinsulinemic-euglycemic clamp, and hepatic insulin sensitivity will be quantified by measurement of hepatic glucose production, gluconeogenesis and glycogenolysis (using stable isotope tracer methods). Subjects will be randomized to an initial period of "normal sleep" or sleep restriction and will be admitted to the Clinical Research Center (CRC) for 9 days to undergo comprehensive metabolic studies and sleep assessments under the assigned sleep condition. After a 1-month washout period, subjects will be re-admitted to the CRC to undergo these same assessments under the opposite sleep condition.

Inclusion Criteria:

• Age 18-45 years
• Regular work hours (ie, no night-time or shift work within the past 6 months)
• Pittsburgh Sleep Quality Index (PSQI) Score <5
• Average nightly sleep duration 6-9 hours (per screening actigraphy)

Exclusion Criteria:

• Current or prior diabetes, gestational diabetes, impaired glucose tolerance or impaired fasting glucose
• Type 2 diabetes in biological parents
• BMI >=25
• Pregnancy
• Chronic medical condition, including: psychiatric disorders, heart disease, pulmonary disease, infectious diseases, rheumatological and neurological disorders
• Use of prescribed medications on a regular basis.
• History of disorder involving hypothalamic, pituitary or adrenal glands
• History of or current sleep disorders (insomnia, restless leg syndrome, sleep disordered breathing, narcolepsy, etc)
• Anemia
• Cognitive impairment