When we eat plants, we take in a large amount of plant cells surrounded by a fibrous complex called a cell wall. A major component of this cell wall is cellulose. Humans do not manufacture the cellulase enzyme needed to digest this type of fiber and must rely on fermentation by the flora in the large intestine.
A protease (also known as a proteolytic enzyme, peptidase or proteinase) is an enzyme that helps digest different kinds of proteins in a process called proteolysis. Proteases are a category of enzymes; some are produced by the body, some are found in foods, and some are produced by bacteria and other microbes. Proteases assist with many different body processes including digestion, immune system function, and blood circulation.