The objectives of the present study are:

1. to evaluate if overnight weight loss is dependent on sleep structure assessed by polysomnography;
2. to compare weight loss rate during sleep and awake rest;
3. to compare night weight loss profile of normal and obese volunteers.

Weight loss can be caused by loss of body mass due to metabolism and by water loss as insensible water loss, sweating, or excretion in feces and urine. Eighty-three percent of the total weight loss is due to insensible water loss from airways and skin. Water loss rate varies according to changes in activity and ambient temperature and humidity. Although weight loss during sleep is a well-known phenomenon, there are no studies relating it to sleep structure or any other functions during the distinct sleep stages, particularly SWS and REM sleep. There is evidence suggesting a homeostatic mechanism for weight control in animal models and humans. This mechanism is thought to be dependent on energy intake, energy expenditure, and environmental conditions. The literature suggests that sleep is important for weight homeostasis on a long term since sleep shortage is associated with overweight status, but overnight weight variation had not yet been studied. Considering these facts, we hypothesized that the overnight weight loss rate is not uniform throughout the sleep period. We also intend to compare weight loss rate during sleep and awake rest.

Intervention: Normal and obese volunteers will undergo whole night polysomnography with continuous body weight and temperature register after an adaptation night. After that, volunteers will remain awake resting in bed during the following day for continuous weight and temperature register.

Inclusion Criteria:

• normal and obese volunteers

Exclusion Criteria:

• serious medical or neurological condition

Normal and obese volunteers