ObjectivesTo assess the amount of nutrients delivered, prescribed, and required for critically ill patients and to identify the reasons for discrepancies between prescriptions and requirements and between prescriptions and actual delivery of nutrition.DesignProspective cohort study.SettingTwelve-bed medical intensive care unit in a university-affiliated general hospital.PatientsFifty-one consecutive patients, receiving nutritional support either enterally or intravenously for ≥ 2 days. We followed patients for the first 14 days of nutritional delivery.Measurements and Main ResultsThe amount of calories prescribed and the amount actually delivered were recorded daily and compared with the theoretical energy requirements. A combined regimen of enteral and parenteral nutrition was administered on 58% of the 484 nutrition days analyzed, and 63.5% of total caloric intake was delivered enterally. Seventy-eight percent of the mean caloric amount required was prescribed, and 71% was effectively delivered. The amount of calories actually delivered compared with the amount prescribed was significantly lower in enteral than in parenteral administration (86.8% vs. 112.4%,p< .001). Discrepancies between prescription and delivery of enterally administered nutrients were attributable to interruptions caused by digestive intolerance (27.7%, mean daily wasted volume 641 mL), airway management (30.8%, wasted volume 745 mL), and diagnostic procedures (26.6%, wasted volume 567 mL). Factors significantly associated with a low prescription rate of nutritional support were the administration of vasoactive drugs, central venous catheterization, and the need for extrarenal replacement.ConclusionsAn inadequate delivery of enteral nutrition and a low rate of nutrition prescription resulted in low caloric intake in our intensive care unit patients. A large volume of enterally administered nutrients was wasted because of inadequate timing in stopping and restarting enteral feeding. The inverse correlation between the prescription rate of nutrition and the intensity of care required suggests that physicians need to pay more attention to providing appropriate nutritional support for the most severely ill patients.