Nutritional Support During Critical Illness This PulmCCM topic review will be periodically updated and expanded as new research is published. Originally published September 22, 2013. Most recent update: January 24, 2019. During critical illness, catabolism (breakdown of muscle protein, fat and other complex molecules) occurs faster than anabolism (synthesis of these same macromolecules). Historically, the major goal of nutritional support during this period of acute illness was to ensure the body has adequate energy and nutrients available to slow down this process of fat and muscle loss. Loss of lean muscle mass during acute illness has been associated with