Nutrition is intimately linked to pulmonary function and an understanding of these relationships have therapeutic utility. Malnutrition is known to be associated with impaired mechanical function of the lung in both chronic and acute respiratory insufficiency. Refeeding results in improvement in functional characteristics and may be critical in the weaning of patients from mechanical ventilation. In contrast, overfeeding may result in an increased ventilatory demand resulting in the inability to wean from respiratory support. This article considers the background as well as recommendations for the nutritional care of patients with acute and chronic respiratory failure.