Basic Nutrition Carbohydrate Digestion, Absorption

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Basic Nutrition CarbohydrateDigestion,
Absorption Metabolism
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Outline Dietary Carbohydrates

• Digestion
• Monosaccharide Transport
• Resistant Carbohydrates
• Metabolism
• Recommendations - DRI

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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

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Monosaccharides are absorbed by specific
transporters at the enterocyte brush border and
basolateral membranes
GLUT2
Fructose
GLUT5
Fructose Glucose Galactose
Fructose Glucose Galactose
Disaccharidases
Fructose Glucose Galactose
Na
K
Glucose Galactose
ATPase
SGLT-1
Na
K
Na
H2O
H2O
Na
Brush border membrane
Basolateral membrane
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Short-Chain Fatty Acids

• Products of fiber fermentation
• Acetate, propionate, butyrate comprise 83 of
  SCFAs
• Found in a fairly constant molar ratio of
  602515
• 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)

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SCFA and Functional Adaptations
glucose uptake
GLUT2
Fructose
GLUT5
Fructose Glucose Galactose
Fructose Glucose Galactose
Fructose Glucose Galactose
Sucrase- Isomaltase
Na
K
Glucose Galactose
ATPase
SGLT-1
Na
K
Na
H2O
H2O
Na
Brush border membrane
Basolateral membrane
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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)

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• 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

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Determining Carbohydrate DRI

• Primary energy source, along with fat
• Preferred substrate for certain metabolic
  pathways
• Body can synthesize de novo
• EAR/ AIs derived from minimum metabolic
  requirements and decreased disease risk

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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

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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

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Carbohydrate DRI Values for Adults
Recommendations change for pregnant or lactating
women