“A cysteine-dependent increase of glutathione was also observed in rats fed a diet containing gelatin with cysteine , but the increase was relatively lowered compared with rats fed a protein-free diet containing the same amount of cysteine.”
“Addition of excess cysteine to the diet masked the effects of gelatin and tryptophan, stimulated glutathione synthesis in the liver as well as incorporation of dietary cysteine into protein fractions.”