CYSTEINE RESTRICTION

Cysteine is a non-essential sulfur containing amino acid. Cysteine is obtained from the diet as cystine which is two cysteine molecules bonded together. Cysteine is also obtained from conversion methionine in limited amounts. Cysteine itself is an antioxidant and is a component of glutathione. Depletion of glutathione can lead to cancer cell death or reversal of chemoresistance.

Experimental evidence demonstrates a high dependence of cysteine in cancer cells and deprivation of cysteine can lead to cancer cell death. Of all of the dietary amino acids, cysteine is the most essential for tumor growth and resistance to treatment. A methionine restricted diet is by default a cysteine restricted diet. The same foods high in methionine are high in cysteine, namely animal proteins. A plant-based diet is lower in cysteine (cystine) than a western diet. For therapeutic purposes, a diet consisting of mostly fruits and select vegetables will limit cysteine to an intake level that will impact cancer cell growth and survival. The addition of vitamin B6 (P5P) will further lower the availability of cysteine.

NORI is the pioneer in applying methionine and cysteine restriction as an element of alternative or integrative cancer treatment. Cysteine is a key dietary target that is proving to be the key to effective treatment free of adverse side effects. Below is a small selection of recent scientific studies focused on cysteine deprivation in cancer.