Gastrointestinal tract lipid digestion

Fats and other lipids are poorly soluble in water. The larger the accessible surface is—i. e., the better the fat is emulsified—the easier it is for enzymes to hydrolyze it (see p. 270). Due to the special properties of milk, milk fats already reach the gastrointestinal tract in emulsified form. Digestion of them therefore already starts in the oral cavity and stomach, where lipases in the saliva and gastric juice are available. Lipids that are less accessible—e.g., from roast pork—are emulsified in the small intestine by bile salts and bile phospholipids. Only then are they capable of being attacked by pancreatic lipase [4] (see p. 270). 

Singh, H., Ye, A., Horne, D.S. (2009). Structuring food emulsions in the gastrointestinal tract to modify lipid digestion. Progress in Lipid Research, 48, 92-100. 

Taurine, which has an amino group in the 6-carbon and a sulfonic acid group instead of COOH, is present in the CNS and as a component of certain bile acids participates in digestion and absorption of lipids in the gastrointestinal tract. 

The clinical abnormalities related to the gastrointestinal tract are not life-threatening and can be treated. In newborns with CF, intestinal obstruction (meconium ileus) can occur in 10-20% of cases due to failure of digestion of intraluminal contents due to lack of pancreatic enzymes in utero. Exocrine pancreatic enzyme deficiency is present from birth affecting both lipid and protein digestion. In general, carbohydrate digestion is not severely impaired. 

Bile fluid performs two important functions (1) the emulsification, solubilization, and transport of lipids and fat-soluble vitamins by the detergent effects of bile acids, and (2) the elimination of many waste products, including bilirubin and cholesterol secreted via the bile into the gastrointestinal tract. Bile acids and bile salts are the principal components of the bile fluid, acting as detergents in the digestion of fat in the intestinal tract. 

Inhibitors of pancreatic lipase (section 4.3.2) do reduce lipid digestion and absorption, and some have been licensed for pharmaceutical use. The problem with their use is that undigested fat in the gastrointestinal tract can cause discomfort and, if enough is present, foul-smelling fatty diarrhoea (steatorrhoea). 

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