<P> Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose . Glucose and galactose can be absorbed by the small intestine . Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat unfermented milk - based foods . This is commonly known as lactose intolerance . Lactose intolerance varies widely by ethnic heritage; more than 90 percent of peoples of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent . </P> <P> Sucrase is an enzyme that breaks down the disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar . Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine . </P> <P> DNA and RNA are broken down into mononucleotides by the nucleases deoxyribonuclease and ribonuclease (DNase and RNase) from the pancreas . </P> <P> Some nutrients are complex molecules (for example vitamin B) which would be destroyed if they were broken down into their functional groups . To digest vitamin B non-destructively, haptocorrin in saliva strongly binds and protects the B molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes . </P>

As part of the digestive process the human stomach