Betaine is a methyl derivative of glycine first isolated from the juice of sugar beets. Betaine is found in many common foods, but concentrated significantly in beets, spinach, wheat foods, and shellfish. In addition, betaine can be synthesized within the human body. Betaine participates in the methionine cycle, which produces vital biomolecules including proteins, hormones, phospholipids, polyamines, and nutrients. Betaine is used as a dietary supplement and has a beneficial effect on the human health. In the USA, FDA approved a betaine-containing drug Cystadane for the treatment of homocystinuria. The drug acts as a methyl group donor in the remethylation of homocysteine to methionine.