Assessment of Nutritional Status After Gastric Bypass Surgery

This study is aimed at assessing how Roux-en-Y gastric bypass (RYGP) impacts on energy and nutrients' intake, energy expenditure, and nutritional status in obese patients. It will try quantitate energy and protein balance after RYGP, and to identify how RYGP effects the intake of various common dietary protein sources 16 female patients with BMI \> 40 kg/m2 and on a waiting list for bariatric surgery will be included. The following measurements will be performed before, and 1, 3, 6, 12, and 36 months after RYGP * body weight * body composition (bio impedancemetry) * basal metabolic rate (open circuit indirect calorimetry) * 24-hour urinary urea excretion * fasting blood chemistry * energy and macronutrient's intake (3-day dietary recall)