Background/aim: The aim of this prospective study was to determine whether the preoperative oral intake of carbohydrate-rich drinks by patients undergoing a coronary artery bypass graft attenuates postoperative insulin requirements, improves postoperative patient discomfort, provides inotropic support, shortens the length of the ICU stay, and shortens the duration of postoperative mechanical ventilation. Materials and methods: This randomized prospective clinical study included 152 patients with coronary artery disease who were divided into 4 groups. Carbohydrates were administered to 3 groups at different hours and doses before operation. The fourth group had an 8-h preoperative fasting period. The inotropic and vasopressor requirements, ventilation time, and ICU stay time were recorded for all of the groups. Patient wellbeing, mouth dryness, hunger, anxiety, and nausea were assessed using VAS scores of 1-10. Results: Mouth dryness and hunger were significantly higher in the control group (P = 0.03, P = 0.02). The increase in blood glucose level was significantly higher in the control group (P = 0.04). The exogenous insulin requirement was significantly higher in the control group than in the other groups (P = 0.04). Conclusion: The administration of carbohydrates before elective cardiac surgery reduced insulin resistance. Based on the VAS scores, the intake of carbohydrates reduced mouth dryness and hunger. Overall, preoperative oral carbohydrate treatments can improve the postoperative outcomes of coronary artery bypass graft surgeries.