Glycogen often referred to as "animal starch" is a multi-branched glucose polysaccharide that is used as a source of energy storage in animals, fungi and bacteria. Glycogen functions as one of two forms of energy reserves, glycogen being stored for the short term and triglyceride being stored in adipose tissue (i.e. body fat) for long-term storage. In humans, glycogen is produced and stored primarily in the liver and skeletal muscle cells.