A prospective, randomized and controlled study is proposed to establish whether an enteral nutrition support regimen based on pressurized whey protein and glucose improves the postoperative utilization of amino acid substrates compared to a drink based on glucose alone. The kinetics of protein metabolism (protein breakdown, protein synthesis and amino acid oxidation) will be investigated using stable isotope methodology before and after surgery in patients undergoing colon resection. Stable isotope infusions will be conducted one week before surgery and on the second postoperative day for two hours in the fasted state and for four hours while sipping the enteral nutrition support regimen. Patients will consume one of two enteral nutrition support regimens consisting of a drink containing either pressurized whey protein and glucose or glucose alone. It is hypothesized that an enteral nutrition support regimen based on pressurized whey protein and glucose promotes positive protein balance through increased protein synthesis or reduced protein breakdown compared to glucose alone.

Inclusion Criteria:

• age older than 18 years
• ASA class I to III
• colorectal surgery for non-metastatic disease (including right, transverse, left, sigmoid, subtotal, total and hemicolectomy and low anterior resection)
• body mass index >17 and <30 kg.m-2
• stable weight over the preceding three months (<10 % body weight loss)
• serum albumin >35 g/L

Exclusion Criteria:

• severe cardiac, renal or hepatic failure
• diabetes
• hyper and hypothyroidism
• active inflammatory bowel or diverticular disease
• musculoskeletal or neuromuscular disease
• anemia (hematocrit <30)
• albumin < 25 g/l
• pregnancy
• use of steroids.