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

Enhanced recovery after surgery (ERAS) programs have progressively shifted perioperative fasting practice away from prolonged fasting toward shorter fasting intervals and the selective use of clear fluids before anesthesia. Preoperative oral carbohydrate loading has been proposed as a metabolic conditioning strategy that may reduce the catabolic effects of fasting, stimulate endogenous insulin secretion, suppress lipolysis, and attenuate the postoperative decline in insulin sensitivity. However, most supporting evidence has been generated in patients without diabetes.

Patients with type 2 diabetes mellitus have baseline insulin resistance, variable pancreatic beta-cell reserve, and altered responses to carbohydrate intake. Surgical stress, anesthesia, pain, and inflammatory responses may further increase hepatic glucose production and reduce peripheral glucose utilization, resulting in postoperative hyperglycemia and worsening insulin resistance. At the same time, prolonged fasting and perioperative changes in glucose-lowering therapy may increase the risks of hypoglycemia and glycemic variability. Therefore, the potential metabolic benefit of preoperative carbohydrate loading in patients with type 2 diabetes must be evaluated together with its effects on perioperative glycemic safety.

This study is designed as a single-center, prospective, three-arm, parallel-group randomized controlled trial in adults with type 2 diabetes undergoing elective gastrointestinal surgery. The trial will compare standard ERAS fasting and non-caloric clear-fluid management with preoperative oral carbohydrate loading. A third group receiving an approximately equivalent amount of glucose intravenously is included as a prespecified mechanistic exploratory comparator.

The principal clinical question is whether preoperative oral carbohydrate loading can attenuate early postoperative insulin resistance compared with standard ERAS fasting management. The primary confirmatory comparison is therefore between the oral carbohydrate group and the standard ERAS group. The intravenous glucose group is not the basis for the primary sample-size calculation and will mainly be used to explore whether any observed metabolic effect is related predominantly to glucose substrate provision or whether the oral gastrointestinal route may provide additional metabolic effects.

To reduce treatment-related heterogeneity, perioperative diabetes management will be standardized as much as clinically feasible. Non-insulin glucose-lowering agents will be discontinued before surgery according to the study protocol and current clinical safety requirements, and insulin-based perioperative glucose management will be used when necessary. Use of insulin, including timing, dose, route, and indication, will be carefully documented because exogenous insulin may influence the interpretation of fasting insulin-based measures of insulin resistance.

Continuous glucose monitoring will be used to characterize perioperative glucose patterns, while point-of-care glucose measurement will be used to confirm clinically important high or low glucose values and to guide treatment decisions. Continuous glucose monitoring data will be analyzed within prespecified perioperative time windows to describe glucose exposure, glycemic variability, and time spent within, above, or below the target glucose range.

Because delayed gastric emptying and aspiration are important concerns in patients with diabetes, individuals with known or suspected gastroparesis, gastric outlet obstruction, upper gastrointestinal obstruction, or other conditions associated with high aspiration risk will be excluded. Gastric antral ultrasonography will be performed before anesthesia as an additional exploratory assessment of gastric contents and aspiration-related safety.

The primary metabolic assessment will focus on insulin resistance on the first postoperative day. Additional metabolic measurements will include glucose, insulin, C-peptide, and selected markers of lipid metabolism, ketone production, and surgical stress. Repeated postoperative measurements will allow evaluation of the early postoperative metabolic trajectory. Perioperative glucose control, patient comfort, postoperative nausea and vomiting, recovery variables, length of hospital stay, postoperative complications, and predefined safety events will also be assessed.

Randomization will be performed in a 1:1:1 ratio using a variable-block randomization sequence with allocation concealment. Because the interventions are visibly different, participants and the personnel administering the interventions cannot be blinded. However, laboratory personnel, outcome assessors, gastric ultrasound assessors, and statistical analysts will remain blinded to treatment allocation whenever feasible.

The study will follow the intention-to-treat principle for the primary analysis. The primary confirmatory analysis will estimate the difference in postoperative day 1 insulin resistance between the oral carbohydrate and standard ERAS groups with prespecified adjustment for clinically relevant baseline covariates. Comparisons involving the intravenous glucose group will be interpreted as mechanistic and exploratory.

This trial is intended to provide clinically relevant evidence regarding the metabolic effectiveness and perioperative safety of preoperative oral carbohydrate loading in carefully selected patients with type 2 diabetes undergoing gastrointestinal surgery, and to help define an evidence-based approach to carbohydrate administration within ERAS pathways for this population.