Background and Aims: The aim of this study was to evaluate the preventive effects of high-fat enteral feeding on glycemic control and clinical outcomes in critically ill patients: a randomized clinical trial. Materials and Methods: This study was done on 42 normoglycemic patients admitted to Intensive Care Unit (ICU). Patients were randomly classified into three groups of 14 each. Control group (A) received carbohydrate-based diet (protein: 20%, fat: 30%, and carbohydrate: 50%), study groups received two types of high-fat diet; Group B (protein: 20%, fat: 45% including half of olive oil and half sunflower oil, and carbohydrate: 35%); and Group C (protein: 20%, fat: 45% including sunflower oil, and carbohydrate: 35%) in the first 48 h of admission. Results: Basal characteristics of participants were the same. After the feeding trial, there was no difference between the groups in mean plasma and capillary glucose levels and insulin requirements. Serum high density lipoprotein (HDL)-cholesterol level was increased significantly in Group B on day 10 compared to admission level (40.75 ± 5.58 vs. 43.56 ± 2.25, P = 0.05). We did not find any difference in organ failure involvement and mortality rate between groups. The number of ICU free days was significantly more in Group B compared to the control group (P = 0.04). Conclusion: High-fat diets have no preventive effect on stress hyperglycemia. High monounsaturated fat diet may increase serum HDL-cholesterol level and decrease the length of stay in ICU.