Fat is broken down into glycerol and fatty acids. Fat breakdown is called lipolysis and is performed by proteins called lipases. Once the fat is broken down, the human body can either utilize it directly for energy or use it to synthesize glucose.
Most fat breakdown occurs in the small intestine and is aided by lipases and bile. Bile is produced in the liver and stored in the gallbladder and aids digestion by emulsifying the fat. A small amount of fat digestion takes place in the mouth and stomach, and the digested fatty acids are absorbed by the body in the large intestine.
Cholesterol is the bile component that transports fat from the large intestine to the rest of the body. Excess cholesterol is reabsorbed into the bloodstream rather than excreted, except when it binds to soluble fiber. A diet high in fiber allows more cholesterol to leave the body.
A healthy digestive system absorbs 95 percent of fat consumed. Diseases such as celiac disease and deficiencies of lipases or bile salts interfere with fat absorption and are collectively called malabsorption disorders. A healthy adult should obtain 30 percent of his daily calories from fat. The typical American diet provides a more than adequate amount of fat for adults without malabsorption disorders.