Amylase and lipase present in saliva starts the breakdown of carbohydrates and fats. Food is then carried through esophagus to the stomach. Stomach produces hydrochloric acid and digestive enzymes. The process of digestion really gets under way, with the breakdown of protein, fat and carbohydrates. Partially digested food then moves to the small intestine.
Small intestine is where the bulk of digestion and absorption takes place.
Various digestive enzymes produced either by the lining of the intestine or by the pancreas continue the breakdown of fats, carbohydrates and proteins. Bile, produced by the liver, helps fat digestion and absorption. As the food travels through the 25 feet of small intestine, it is reduced to molecules of sugars, amino acids and fatty acids, which are then absorbed through the wall of the small intestine. The remaining unabsorbable matter moves to the large intestine. It continues the process, compressing undigested material by removing water.