Fatty acid metabolism months, and, during this entire period, the energy is derived from degradation of fat stores. Migrating birds similarly build up large fat reserves before embarking on their intercontinental journeys. Thus the young adult human’s fat stores average between about 10–20 kg, but varies greatly depending on age, gender, and individual disposition. By contrast the human body stores only about 400 g of glycogen, of which 300 g is locked inside the skeletal muscles and is unavailable to the body as a whole. The 100 g or so of glycogen stored in the liver is depleted within one day of starvation.
Glycogen debranching enzyme as Glycogen storage disease type III can result. Glucosyltransferase and glucosidase are performed by a single enzyme in mammals, yeast, and some bacteria, but by two distinct enzymes in "E. coli" and other bacteria, complicating nomenclature. Proteins that catalyze both functions are referred to as glycogen debranching enzymes (GDEs). When glucosyltransferase and glucosidase are catalyzed by distinct enzymes, "glycogen debranching enzyme" usually refers to the glucosidase enzyme. In some literature, an enzyme capable only of glucosidase is referred to as a "debranching enzyme". Together with phosphorylase, glycogen debranching enzymes function in glycogen breakdown and glucose mobilization. When phosphorylase has digested