The purpose of this study is to determine the effect of different time of sleep restriction on control of food intake and metabolism of obese and normal subjects.

The reduction of sleep time has now become a common habit, driven by the demands and opportunities of modern society. Some studies have suggested that sleep restriction would be an important factor in predisposing to obesity. However studies of sleep restriction in obese individuals have not yet been conducted. Still, the time of sleep restriction varies greatly between studies, making it difficult to compare results.

The investigators aim to recruit 20 young adults, 10 obese and 10 normal weight individuals. The study will be conducted as a randomized, crossover study with three conditions. Each participant will be subjected to reduction of the beginning of sleep (from 3-7h), reduction of the end of sleep (from 23-3h), and normal sleep (from 23-7h), in random order, for three consecutive nights.

In each condition, subjects will stay for 4 days in the laboratory. Three control meals will be offered. Visual analogue scales will be applied before and after each meal to assess hunger and appetite for different food categories. Blood samples will be collected hourly during 24 hours.

Inclusion Criteria:

• obese (BMI>30) and normal weight (BMI between 19 and 24,9)
• regular time of sleep between 6.5 and 8 hours

Exclusion Criteria:

• self-reported sleep problems (Pittsburgh Sleep Quality Index score >5);
• Obstructive sleep apnea (AHI > 5 in polysomnography)
• night work;
• variable sleep habits or habitual daytime naps;
• regular physical exercise (>3 hours/week);
• excessive intake of alcohol (>7 drinks/week);
• excessive intake of caffeine (>300 mg/day);
• smoking;
• substance abuse;
• use of prescription medications or over-the-counter drugs affecting sleep or metabolism;
• chronic diseases (e.g. cancer, asthma, back pain, thyroid disease, heart disease, diabetes, etc.)
• history of neurological, medical or sleep disorders;
• trans-meridian travelling the last month;
• chronotype: extreme morning or extreme evening
• unable to comply with the protocol.

primary care clinic, community sample, residents of the city of Sao Paulo