['The metabolic response to surgery includes a net loss of proteins that influences negatively the clinical evolution of the patients. We investigated the effect of perioperative nutrition on protein metabolism alterations immediately after surgery.', 'A control group of 21 surgery patients were submitted to conventional perioperative nutritional protocol (18 h of fasting plus low-dose glucose after surgery). An experimental group of eight similar patients was given complete parenteral nutrition during 24 h before and 24 h after surgery. Nitrogen balance, whole body protein synthesis, breakdown, and 3-methylhistidine were determined before surgery and 24 h after surgery.', 'The immediate response to surgery with conventional nutritional management was a net protein loss (-1.023 g prot. kg(-1) day(-1)), caused by an increase in the protein breakdown (137.9% of preoperative values), while the protein synthesis remained unchanged (98.4%). The 3-methylhistidine excretion was not increased in respect to perioperative values, suggesting that the degraded protein was not from muscular origin. The experimental group with perioperative nutrition showed neither protein loss (+0.075 g prot. kg(-1) day(-1)) nor changes in protein synthesis or breakdown vs. preoperative values (96.3% and 88.0%, respectively).'] Does perioperative nutrition prevent the early protein losses in patients submitted to gastrointestinal surgery?