Protein-calorie malnutrition as evidenced by loss of weight or of lean body mass is a commonly seen disorder. Although its cause is clearly multifactorial, objective measures of protein-calorie malnutrition have been repeatedly correlated with poor patient outcomes. Total parenteral nutrition was developed to halt or reverse this disorder, but its ability to improve the short- to intermediate-term outcome in patients with impaired nutrient intake has been highly inconsistent. Factors influencing this variable outcome include the degree of functional impairment in the treatment group, the underlying disease causing the impaired intake, and possibly the amount and composition of nonprotein calories delivered. In particular, considerable evidence points to intravenous soybean oil emulsion as a negative factor in the nutritional support of stressed patients. Taken in combination, current information suggests reserving the use of parenteral feeding for patients meeting objective criteria for protein-calorie malnutrition and making parsimonious use of lipid emulsion, especially in stressed patients.