Amino acids are the "alphabet" of protein structure, determining many of the properties of proteins. Amino acids are rapidly absorbed and readily available in the blood. In the cell, amino acids maintain protein stores and counteract hormone-mediated catabolic stimuli. Thus, amino acid supplementation may be effective in counteracting the metabolic and morphologic consequences of the hypercatabolic state of chronic diseases such as heart failure, diabetes mellitus, or liver cirrhosis.