Protein digestion and absorption in man. Normal mechanisms and protein-energy malnutrition.

Protein is an essential nutrient normally assimilated in an efficient manner following the action of gastric, pancreatic and small intestinal enzymes. After hydrolysis, protein digestion products in the form of amino acids and small peptides undergo mucosal uptake by distinct transport mechanisms. Although gastric and pancreatic enzymes are important, the small intestine appears to be the critical rate-limiting tissue in this process. Impaired intake, assimilation or excessive enteric protein loss may occur with several diseases leading to protein-energy malnutrition. Although the clinical and laboratory features of this condition are nonspecific and wide ranging in spectrum, their presence may provide a clue to underlying disease and serve as an index of patient nutritional status. Disease of the exocrine pancreas or small intestine may cause significant protein-energy malnutrition which, in turn, can cause major structural and functional abnormalities in these tissues.