Serine is found in soybeans, nuts, eggs, lentils, shellfish, and meats.

Serine is a nonessential amino acid used in protein biosynthesis and can be derived from four possible sources: dietary intake, degradation of protein and phospholipids, biosynthesis from glycolysis intermediate 3-phosphoglycerate, or from glycine.

Serine is used to synthesize ethanolamine and choline for phospholipids. Serine is essential for the synthesis of sphingolipids and phosphatidylserine in CNS neurons.

In the folate cycle, glycine and serine are interconverted. These methyltransferase reactions and interconversions are readily reversible depending on the needs of the folate cycle. Dietary serine is not fully converted to glycine; therefore, serine supplementation has little value, though is not harmful.

Glycine and serine’s interconversion are important in mitochondrial glycolysis. Glycolysis provides ATP and energy in most cell types. Serine-glycine biosynthesis is a component in glycolysis-diverting pathways and nucleotide biosynthesis. This is clinically important, and specifically evident, in cancer. Cancer cells use glycolysis to sustain anabolism for tumor growth. Genetic and functional evidence suggests that abnormalities in the glycine-serine pathway represent an essential process in cancer pathogenesis by promoting energy production and promoting defective purine synthesis.

Serine is also a cofactor for the transsulfuration enzyme cystathionine-β-synthase making its availability important for glutathione production.