 Surgical stress creates a state of insulin resistance which has been related to increased postoperative complications. Fasting before surgery induces a catabolic state that contributes to the development of insulin resistance. The aim of this study is to evaluate the effect of preoperative oral carbohydrates on postoperative insulin resistance in patients undergoing OPCAB off-pump coronary artery bypass surgery. Sixty patients, aged 20 to 79 years, scheduled for OPCAB will be divided into carbohydrate n30 and control n30 groups. Randomly selected patients of the carbohydrate group are given 400ml of 12.8 g100 ml carbohydrate beverage in the evening before surgery and in the morning of the operation day 3 hours before their scheduled operation. In contrast, patients in the control group consume no food or drink after midnight before their surgery. The primary endpoints are postoperative insulin resistance measured by short insulin tolerance test. 