Galactose and fructose are two other monosaccharides that can
provide fuel for cellular metabolism; however, their role is much less
significant than that of glucose. Galactose is derived from lactose
(galactose + glucose), which is found primarily in milk
and milk products. If necessary, galactose can be incorporated into
glycogen via galactose-1-phosphate and glucose 1-phosphate, becoming
a source of glucose. Galactose is also an important component for
certain glycolipids, glycoproteins, and glycosaminoglycans. The
two dietary sources of fructose are sucrose (fructose + glucose),
a commonly used sweetener, and fructose, which is found in fruits,
vegetables, and honey.