Colorectal surgery patients face excessive catabolism, increasing inflammation and immune compromise. The administration of nutritional supplements known as immunonutrition before gastrointestinal surgery has been shown to improve clinical outcomes; however, the mechanisms underlying these benefits remain inconclusive.

The objective of the study is to evaluate the effect of preoperative nutritional supplementation with an immunonutrient-enriched formula compared to an isocaloric and isoproteic formula on plasma BCAA concentration in patients undergoing elective colorectal surgery. A double-blind, randomized controlled clinical trial will be conducted. Patients will be required to drink the supplement daily for the 7 days preceding the surgical intervention. Patients in both groups will be instructed to maintain their usual food intake. During the study, there will be two patient assessments and a review of medical records to document the outcomes.

Patients undergoing colorectal surgery, experience excessive and persistent catabolism, leading to skeletal muscle depletion, and increased inflammatory and immunological involvement, this results in greater malnutrition, mortality, and postoperative morbidity. Depletion of amino acids leads to an increased inflammatory response and diminished immunity. Guidelines of leading international societies in the field of clinical nutrition recommend the perioperative administration of oral formulas with immunonutrients in these patients. The administration of nutritional supplements known as immunonutrition (fortified with arginine, glutamine, branched-chain amino acids (BCAAs) and omega-3 polyunsaturated fatty acids) before gastrointestinal surgery has been shown to improve clinical outcomes, such as a reduction in post-surgical infectious, reduced risk of anastomotic leakage and fewer days of hospital stay; however, the mechanisms related to these benefits are not conclusive.

The aim of the study is to evaluate the effect of preoperative nutritional supplementation for 7 days with a formula enriched with immunonutrients compared to an isocaloric and isoproteic formula, on the plasma concentration of BCAAs in patients undergoing elective colorectal surgery. A randomized, double-blind, controlled trial will be conducted with 63 patients per group. The concentration of BCAAs will be measured prior to the 7 days of nutritional supplementation and will be repeated on the day of the surgical intervention before the procedure. The supplements for both groups will provide 500 calories, 41 g of protein, 60 g of carbohydrates, and 11 g of lipids; the supplement for the intervention group is additionally fortified with immunonutrients. Patients will be instructed to consume the supplement daily for the 7 days prior to the surgical intervention. Patients in both groups will be advised to maintain their usual food intake.

The investigators hypothesized that if an oral formula with immunonutrients is administered compared to an isocaloric and isoproteic formula without them for 7 days in the preoperative period in patients undergoing elective colorectal surgery, there will be an increase in the plasma concentration of BCAAs in the intervention group.

Inclusion Criteria:

• Both sexes
• Over 18 years of age
• Scheduled for elective colorectal surgery (Resection and intestinal reconnection)
• Obtaining patient consent

Exclusion Criteria:

• Consumption of nutritional supplements during the 2 weeks prior to patient enrollment
• Consumption of additional nutritional supplements during the 7 days corresponding to the study intervention period
• Patients diagnosed with chronic kidney disease
• Patients diagnosed with hepatic cirrhosis
• Documented allergy to any of the ingredients in the formulas under evaluation (milk and/or soy).