Our ancestors ate whole animals. Skin, cartilage, tendons, bones, organs. That meant they consumed massive amounts of glycine from collagen rich tissues. Modern humans eat almost exclusively muscle meat, which is extremely high Glutathione vs. NAC: An Expert Comparison of Antioxidants Transparent Labs Figure 3 from Glutathione synthesis. Semantic Scholar Glutathione Dependent Pathways in Cancer Cells Appraising the Role of Astrocytes as Suppliers of Neuronal Glutathione Precursors