title: Carbohydrate intolerance.
abstract: OBJECTIVE
  The small intestinal mucosa is highly specialized for terminal digestion of nutrient polysaccharides and disaccharides and absorption of monosaccharides. However, in the case of digestive or absorptive deficiency, symptoms of carbohydrate intolerance result. Significant progress has been made toward defining the molecular genetic mechanisms responsible for several carbohydrate intolerances.
  
  
  RESULTS
  This review summarizes monosaccharide and disaccharide intolerance conditions and recent clinical and basic science reports related to carbohydrate digestion and membrane transport. Genetic polymorphisms closely associated with lactase persistence/nonpersistence have been identified. Lactose intolerance is capable of preventing the achievement of adequate peak bone mass in susceptible young adults and may predispose to osteoporosis. Recent studies support previous reports that fructose malabsorption is associated with unexplained gastrointestinal symptoms. GLUT2 may be recruited from the basolateral to the apical membrane of enterocytes to facilitate small intestinal fructose absorption.
  
  
  CONCLUSIONS
  Knowledge regarding the clinical aspects of and the physiologic mechanisms responsible for specific carbohydrate intolerances has allowed for improved diagnostic and treatment options and has contributed to continuing investigation of intestinal gene expression.
authors.affiliation: Stanford University School of Medicine, Stanford, California 94304, USA. eric.sibley@stanford.edu
authors.forename: Eric
authors.initials: E
authors.lastname: Sibley