Patients undergoing sleeve gastrectomy as bariatric procedure ara randomized into 3 groups: those patients receiving a preoperative regular diet of 900 Kcal/day (Group 1), those receiving preoperative balanced energy high protein formula (Group 2) and those receiving preoperative Immunonutrition formula (Group 3). Postoperative pain and acute phase reactants at 24hours after surgery are investigated.