Nearly half of all Americans are obese and/or have been diagnosed with diabetes, accounting for over 327 billion dollars in health care costs in the United States each year. Increasing evidence suggests that chronic short-sleep durations contribute to these diseases, but the specific mechanisms as to how short-sleep durations results in weight gain and diabetes are debated.
Reports of weight gain due to sleep restriction do not comply with the energy balance hypothesis, which would predict that with an increased amount of wakefulness and an associated increase in energy expenditure, there would be a negative shift in energy balance and resulting weight loss over time. Restricting sleep in the laboratory, however, pushes participants towards a positive energy balance via increased daily energy intake when access to food is ad libitum.
The goals of this study are to uncover the impact of chronic sleep restriction, circadian timing, and their combination on energy intake patterns, determine the influence of chronic sleep restriction on food choice when there is equal opportunity to eat at all circadian times, and discover the impact of chronic sleep restriction, circadian timing, and their combination, on glucose tolerance.
1. Ambulatory monitoring: Participants will maintain a consistent 7-day at home 8h sleep schedule at habitual times before both laboratory visits to ensure 1) subjects are not sleep restricted and 2) that they are obtaining the same light-dark schedule prior to each laboratory visit for stable entrainment; verified by actigraphy, sleep logs, and call-ins to a time stamped recorder. Drugs, medications, caffeine, alcohol, and nicotine will be prohibited to use during this time and toxicology analysis will be performed upon admission.
2. Outpatient diet: For 3-days prior to each protocol, participants will consume an outpatient isocaloric diet designed to meet individual daily energy requirements. The diet will consists of a breakfast, lunch, dinner, and snack and participants will be trained by staff in how to prepare the meals. Participants will be instructed to only consume the food provided during these 3-days and be asked by staff to confirm this is all they ate via daily check-ins to ensure adherence.
3. Inpatient protocols: Participants will be admitted to an individual room free of external time cues (e.g. clocks, radios, computers, visits and sunlight). Room temperature is maintained at 21 - 22.2 degrees Celsius and light intensity set at ≤5 lux during forced desynchrony procedures and 0 lux (darkness) during scheduled sleep opportunities. Participants will be instrumented for full polysomnography (PSG) and given a telemetry pill for continuous core body temperature measurement. An 18-gauge IV catheter will also be inserted into the forearm and connected to a triple-stopcock manifold via an IV loop with a 12-foot small-lumen extension cable through which blood sampling can continue in the next room without disturbing leisure activity or sleep.
After instrumentation, participants will be given an 8h sleep opportunity at habitual timing (determined via actigraphy) and will be awakened at habitual wake time in dim-lighting for a baseline "day". During baseline, participants will be given three energy-balanced meals. After baseline, participants' sleep/wake schedule will be advanced by 4h daily for the next 12 calendar days with the participants having access to ad libitum food. Prior to arriving to the laboratory, participants will be randomized to either sleep restriction first (equivalent to obtaining 5.5h of sleep per 24h; n=10) or control conditions first (equivalent to 8h sleep per 24h; n=10); crossover to the other condition will occur on day 8 of the protocol. Because the protocol requires participants to live on a 20h-day, during the control condition participants will experience 13.33-hour wake episodes followed by 6.67-hour sleep opportunities, while during the sleep restriction condition they will experience 15.33-hour wake episodes followed by sleep episodes of 4.67 hours long, in the range typically experienced by individuals who habitually restrict their sleep. Providing ad libitum food during this time will be accomplished, as done previously, by providing participants a breakfast, lunch and dinner at \~130-150% more calories than their baseline day and switching out sets of snacks between meals - "morning" (between breakfast and lunch), "afternoon" (between lunch and dinner), and after-dinner (between dinner and sleep). Snacks will be of a variety of healthy (i.e., grapes, low-fat yogurts, whole-grain crackers, nuts, etc.) and unhealthy (i.e., ice cream, cookies, chips, sodas, etc.) options and participants will not need to ask or record what they eat.
