The plasma level of glutathione (GSH) is typically depleted in individuals with metabolism related disorders. However, cellular GSH levels cannot be increased by supplementing GSH and it must be synthesized within the liver either de novo or by salvation pathway. The investigators found that the level of GSH is not enough to maintain and regulate the thiol redox status of the liver in subjects with high hepatic steatosis at fasting stage due to the depletion of glycine. Glycine can be synthesized via the interconversion of serine through serine hydroxymethyl transferases (SHMT1 and SHMT2) with concomitant conversion of tetrahydrofolate (THF) into 5,10-methylene-THF (CH2-THF). It has been shown that the serine synthesis is downregulated in patients with NAFLD and supplementation of serine has attenuated alcoholic fatty liver by enhancing homocysteine metabolism in mice and rats.