This prospective randomized, controlled clinical study was carried out in the Department of Anesthesiology and Intensive Care Unit and Department of Surgery at the Cantonal Hospital Zenica, Bosnia and Herzegovina. After obtaining ethical committee approval 50 participants, scheduled for elective open colon surgery were included into study. Sample size was estimated using sample size calculator software and power analysis with 95% confidence interval and power of 80%. Statistical significance was considered as p\< 0,05. The calculation indicated 19 participants per group would be sufficient to detect a 50% difference for insulin resistance between the groups. Assuming dropout would lead to a total sample size of 50 participants. Before each participant agreed to the join the study, the purpose and procedures of the study were fully explained and informed and written consent was obtained from each participant. A preoperative anesthetic examination was conducted the day before surgery. The participants who fulfilled study criteria were randomly allocated into two groups of 25 participants, depending on the preoperative treatment. The intervention group, received preoperative carbohydrate oral supplementation (CHO group) and the control group (FAST group) underwent to a conventional routine of preoperative fasting. Randomization was performed by computer generated randomization codes. The codes which indicated the treatment were held in sealed opaque envelopes. Nurse who conducted randomization and opened the envelopes the night before surgery was blinded to the study protocol as well as the surgeons, nurses, anesthesiologists and staff involved in data collection.

The participants of FAST group were undergone to the traditional concept of preoperative fasting before surgical procedure. The participants in the intervention group received carbohydrate oral supplement at 10:00 pm the evening before surgery and again on the day of surgery, 2 hours before induction of anesthesia. Assessment of clinical parameters started at 06:00 am on the day of surgery (basal value). The fasting peripheral venous blood samples were collected to measure serum levels of glucose, insulin, C-reactive protein, albumin and IL-6, and further 6 hours post-surgery, at 06.00 am on the first postoperative day and at 06:00 am on the second postoperative day. All patients underwent general anesthesia followed by colon surgery. Assessment of subjective well-being was performed immediately before induction into anesthesia using a 10 cm horizontal Visual Analogue Scales and then repeated for 0-4, 4-8, 8-12 and 12-24 hours post-surgery. Pain at rest, pain with mobilization, thirst, hunger, mouth dryness, anxiety and weakness were evaluated. The patients were explained how to use the scale. Surgical outcome was evaluated by postoperative return of gastrointestinal function, time to independent ambulation and postoperative discharge day. Postoperative data included and the time to oral intake. The following data were recorded also: age, sex, body weight, body mass index, American Society of Anesthesiologists (ASA) physical status class, nutritional status of the participants according to Nutritional Risk Screening 2002 (NRS-2002), tumor localization, type of surgery, duration of surgery, preoperative fasting time and, blood loss during surgery