Clinical and nutritional benefits of cysteine-enriched protein supplements.

PURPOSE OF REVIEW: To review recently published research into the use of dietary cysteine and/or its derivatives as functional food supplements that will enhance antioxidant status and improve outcome in certain diseases.

RECENT FINDINGS: L-cysteine is now widely recognized as a conditionally essential or (indispensible) sulphur amino acid. It plays a key role in the metabolic pathways involving methionine, taurine and glutathione (GSH), and may help fight chronic inflammation by boosting antioxidant status. In stressed and inflammatory states, sulphur amino acid metabolism adapts to meet the increased requirements for cysteine as a rate-limiting substrate for GSH. Critically ill patients receiving enteral or parenteral nutrition, enriched with cysteine, exhibit decreased cysteine catabolism and improved GSH synthesis. The naturally occurring cysteine-rich proteins, whey or keratin, have the potential to be manufactured into high quality, high cysteine-containing functional foods for clinical investigation.

SUMMARY: Cysteine-rich proteins, such as keratin, may have advantages over the simple amino acid or its derivatives, as nutraceuticals, to safely and beneficially improve antioxidant status in health and disease.