The purpose of this study is to test the effects of sleep and meal timing, independent of sleep duration, on glucose regulation and metabolic and hormonal control of energy balance in normal weight adults.

This study will be a 4-phase, randomized controlled study of 5 days each in which participants will undergo 2 phases of late sleep times that differ in meal timing (normal or late) and 2 phases of normal sleep times that differ in meal timing (normal or late).

The Aims and Hypotheses of this study are:

Aim 1: To compare hormonal regulation of food intake and metabolic risk markers in response to altered sleep and meal timing.

• Hypothesis 1: There will be an interaction between sleep and meal time on glucose, insulin, and glucose and insulin area under the curve after the glucose tolerance test such that the late sleep/late meal will result in the worst metabolic profile, normal sleep/late meal and late sleep/normal meal will have an intermediate profile, and normal sleep/normal meal will result in the best metabolic profile.
• Hypothesis 2: There will be an interaction between sleep and meal time on leptin and ghrelin concentrations such that the late sleep/late meal timing phase will result in low leptin/high ghrelin, normal sleep/late meal timing and late sleep/normal meal will have an intermediate profile, and normal sleep/normal meal timing will result in high leptin/low ghrelin.

Aim 2: To compare food intake over a 24-h period in response to altered sleep and meal timing.

• Hypothesis 3: Energy and fat intakes will be greater during the late sleep timing phase compared to normal sleep timing.

Inclusion Criteria:

• Body mass index 22-25
• Normal scores on sleep questionnaires (PSQI, ESS, Berlin, SDIQ)
• Normal score on Beck Depression Inventory
• Intermediate chronotype on Composite Scale of Morningness/Eveningness

Exclusion Criteria:

• Neurological, medical, or psychiatric disorders
• Eating disorders
• Diabetes
• Sleep disorders
• Travel across time zones
• History of drug/alcohol abuse
• Caffeine intake >300 mg/d
• Excessive daytime sleepiness
• Pregnancy or within 1 y post-partum