The digestion of food lipids consists of a series of enzyme-catalyzed steps resulting in absorbable components. Food lipids (fats and oils) are digested initially in the mouth and then in the stomach and intestine. The digestion of lipid is begun in the mouth with the mastication of food and its mixing with the acid-stable lingual lipase. The mixing action separates the lipid particles, exposing more surface area for enzyme action and providing the opportunity for emulsion formation. These changes in physical state are essential steps that precede absorption. In the stomach, the proteins of lipid-protein complexes are denatured by gastric hydrochloric acid and attacked by the proteases (pepsin, parapepsin I, and parapepsin II) of the gastric juice with the resultant release of lipid. Little degradation of fat occurs in the stomach except that catalyzed by lingual lipase. Lingual lipase originates from glands in the back of the mouth and under the tongue. This lipase is active in the acidic environment of the stomach. However, because of the tendency of lipid to coalesce and form a separate phase, this lipase has limited opportunity to attack triacylglycerols. Those that are attacked release a single fatty acid, usually a short- or medium-chain one. The remaining diacylglycerol is subsequently hydrolyzed in the duodenum. In adults consuming a mixed diet, lingual lipase is relatively unimportant. However, in infants having an immature duodenal lipase, lingual lipase is quite important. In addition, this lipase has its greatest activity on the triacylglycerols commonly present in whole milk. Milk fat has more short- and medium-chain fatty acids than fats from other food sources.