Patients who become critically ill can have problems maintaining nutritional intake and it can be challenging for nurses to provide nutritional support. No one assessment method can identify each patient's risk of malnutrition, so nurses need to look at different aspects in their nutritional assessment and refer for specialist help from dietitians and nutrition support teams when needed. This article focuses on how severe physiological stress affects patients who are critically ill and impacts on their nutritional requirements. A nursing nutritional assessment is explored, as are nutritional support methods that may be used to manage these patients' nutritional needs.