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Download Carbohydrates - Absorption and Metabolism
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Basic Nutrition – Carbohydrate Digestion, Absorption & Metabolism Outline – Dietary Carbohydrates 1. 2. 3. 4. 5. Digestion Monosaccharide Transport Resistant Carbohydrates Metabolism Recommendations - DRI The pancreas • Pancreatic duct penetrates duodenal wall • Endocrine functions • Insulin and glucagon • Exocrine functions • Majority of pancreatic secretions • Pancreatic juice secreted into small intestine – Carbohydrases pancreatic alpha-amylase – Lipases – Nucleases – Proteolytic enzymes Monosaccharides are absorbed by specific transporters at the enterocyte brush border and basolateral membranes GLUT2 Fructose GLUT5 Disaccharidases Glucose Galactose H2O Na+ Brush border membrane Fructose Glucose Galactose SGLT-1 H2O Na+ Fructose Glucose Galactose K+ Na+ Fructose Glucose Galactose Na+ ATPase K+ Basolateral membrane Short-Chain Fatty Acids • Products of fiber fermentation • Acetate, propionate, butyrate comprise 83% of SCFAs • Found in a fairly constant molar ratio of 60:25:15 • Enhance structure and function in adult rodent small intestine • mucosal proliferation in colon, ileum and jejunum (Sakata, 1987; Kripke et al., 1989; Koruda et al., 1990) • transporter activity (Tappenden et al., 1997, 1998; Tappenden and McBurney, 1998) SCFA and Functional Adaptations glucose uptake GLUT2 Fructose GLUT5 Fructose Glucose Galactose SucraseIsomaltase Glucose Galactose H2O Na+ Brush border membrane SGLT-1 H2O Na+ Fructose Glucose Galactose K+ Na+ Fructose Glucose Galactose Na+ ATPase K+ Basolateral membrane What are Dietary Reference Intakes (DRI)? • Daily nutrient consumption recommendations • Collective term including: • Estimated Average Requirement (EAR) • Recommended Dietary Allowance (RDA) • Adequate Intake (AI) • Tolerable Upper Intake level (UL) EAR - Meets the requirement of half the healthy individuals in life stage group RDA - Meets the requirement of 97-98% of the healthy individuals in life stage group (RDA = EAR + 2 × SDrequirement) AI - Experimentally determined approximations for healthy individuals in life stage group (used when no RDA set) UL - Highest average daily nutrient intake level that is likely to pose no risk of adverse health effects Determining Carbohydrate DRI • Primary energy source, along with fat • Preferred substrate for certain metabolic pathways • Body can synthesize de novo • EAR/ AI’s derived from minimum metabolic requirements and decreased disease risk Optimal Carbohydrate Level • Amount necessary for optimal health unknown • Populations consuming minimal CHO for long periods show no decrease in longevity • In absence of CHO, adequate protein and dietary fat needed to provide amino acids and glycerol respectively, for gluconeogenesis • Brain, red and white blood cells, medulla of kidney have absolute glucose requirement Setting the Carbohydrate DRIs • In fasted adults, glucose production is about 2.8 to 3.6 g/kg/d • This equals 210 to 270 g/d in a 70-kg man • Minimum amount required determined by brain usage • Brain glucose requirement reported to be 110 to 140 g/d Carbohydrate DRI Values for Adults Function Age Males Females* AMDR (% total RDA/ RDA/AI energy) AI g/d g/d Primary energy 19-30y 130 source for brain, source of calories to 31-50y 130 maintain body weight 130 45-65 130 45-65 50-70y 130 130 45-65 >70y 130 45-65 130 *Recommendations change for pregnant or lactating women
