Preoperative Oral Carbohydrate Loading in Patients With Type 2 Diabetes Undergoing Gastrointestinal Surgery

This study is a single-center randomized controlled trial in adults with type 2 diabetes who are scheduled for elective gastrointestinal surgery. The study aims to find out whether drinking a carbohydrate-containing clear liquid before surgery can reduce early postoperative insulin resistance and improve blood glucose stability without increasing the risk of high or low blood glucose. Participants will be randomly assigned in a 1:1:1 ratio to one of three groups. The first group will receive standard enhanced recovery after surgery (ERAS) fasting and clear-fluid management without a carbohydrate-containing drink. The second group will drink 400 mL of a 12.5% maltodextrin carbohydrate solution, providing about 50 g of carbohydrate, approximately 2 hours before anesthesia. The third group will receive 500 mL of 10% glucose solution intravenously over approximately 2 hours before anesthesia. The intravenous glucose group is included mainly to help explore whether the route of carbohydrate administration affects the metabolic response. All participants will receive standard perioperative care. Blood glucose will be monitored during the perioperative period, including continuous glucose monitoring when available, with point-of-care blood glucose testing used to confirm clinically important high or low glucose readings and to guide treatment when necessary. The primary outcome is insulin resistance on the first day after surgery, measured using the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), which is calculated from fasting blood glucose and fasting insulin concentrations. Secondary outcomes include perioperative glucose levels and glucose variability, time spent within, above, and below the target glucose range, insulin and C-peptide levels, postoperative nausea and vomiting, patient comfort, postoperative recovery, hospital stay, postoperative complications, and safety events such as hypoglycemia, severe hyperglycemia, reflux, or aspiration. The main comparison of interest is between the oral carbohydrate group and the standard ERAS group. The intravenous glucose group will be analyzed mainly as a mechanistic exploratory group.