Hypercatabolic syndrome (HS) is a biochemical state characterized by increased circulating catabolic hormones (eg, cortisol, catecholamines) and inflammatory cytokines (eg, tumor necrosis factors, interleukin–1β), and decreased anabolic insulin effects with consequent insulin resistance. The most important metabolic consequence of HS is the skeletal and cardiac muscle protein breakdown that releases amino acids (AAs), which in turn supports indispensable body energy requirements but also reduces skeletal and cardiac physiologic and metabolic functions. HS occurs in many diseases such as diabetes mellitus, chronic heart failure, chronic obstructive pulmonary disease, renal and liver failure, trauma, sepsis, and senescence. All of these conditions have predominant catabolic molecules with significant muscular wasting and metabolic impairment. Macronutrients such as AA supplements, taken together with conventional therapy, may maintain muscular protein metabolism and cell functions.