The main sources of galactose in the human diet are milk and milk products. The disaccharide lactose from these sources is hydrolyzed in the intestine to its constituent monosaccharides, glucose and galactose. Galactose is metabolized primarily in the liver in a sequence of three reactions that yield one molecule of glucose 1-phosphate per molecule of galactose. First, it is phosphorylated to yield galactose 1-phosphate. Then, galactose 1-phosphate and UDP-glucose react to form UDP-galactose and glucose 1-phosphate, and UDP-galactose undergoes epimerization to form UDP-glucose. In a reaction shared with other pathways, glucose 1-phosphate can be converted into glucose 6-phosphate (Holton et al. 2001; Elsas and Lai 2001).