Sulfur amino acids are involved in central metabolic processes. The sulfur-containing amino acids, methionine and cysteine, are required for diverse, critical biologic functions, including protein synthesis, methylation, fatty acid metabolism, osmotic regulation and regulation of cell division and growth (1-5). Methionine (Met) is an essential amino acid and is metabolized in individuals by the transulfuration pathway to form cysteine (Cys) (6). In addition to use in the primary sequence of most proteins, both Met and Cys are required for other metabolic functions. Met is converted to S-adenosylmethionine, which is used for methylation reactions (1) for structural and functional modifications of proteins, RNA and DNA, as well as synthesis of phospholipids and signaling molecules. Cysteine is used for biosynthesis of glutathione (GSH) and sulfate (2). GSH functions in redox regulation (7) and detoxification of oxidants and reactive electrophiles (8); sulfate is used as a structural component of oligosaccharides (3), transport of steroid hormones (4) and detoxification of foreign compounds (9). Because the SAA are irreversibly modified in the aforementioned processes, there is a requirement for adequate sulfur amino acid intake that extends beyond the need for adequate amounts to maintain normal protein synthesis and turnover.