During the actual operation, tissues are carefully dissected and incised to minimize tissue trauma, then reapproximated with care. A major goal of nutritional support in the trauma patient is to aid host defense by balancing the energy and nitrogen expenditures that occur following injury. Undernutrition may, however, compromise the available host defense mechanisms and thereby increase the likelihood of invasive sepsis, multiple organ system failure, and death. The period of catabolism initiated by surgery and characterized by a combination of inadequate nutrition and alteration of the hormonal environment has been termed the “adrenergic-corticoid phase.” Nutritional support is an essential part of the metabolic care of the critically ill trauma patient and should be instituted before significant weight loss occurs. Nutrition is extremely important to the care of surgical patients because of the changes in their metabolism that surgery, trauma, or sepsis induce.