basic nutrition – carbohydrate digestion, absorption & metabolism
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Basic Nutrition – Carbohydrate
Digestion, Absorption & Metabolism
Outline – Dietary Carbohydrates
Outline – Dietary Carbohydrates
1.Digestion2.Monosaccharide Transport3.Resistant Carbohydrates4.Metabolism5.Recommendations - DRI
• 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
The pancreasThe pancreas
Monosaccharides are absorbed by specific transporters at the enterocyte brush border and basolateral membranes
Monosaccharides are absorbed by specific transporters at the enterocyte brush border and basolateral membranes
Brush bordermembrane
Basolateralmembrane
Fructose GlucoseGalactose
GlucoseGalactose
Na+
Na+
Na+
K+
Fructose
SGLT-1
GLUT5
Na+
K+ ATPase
GLUT2
Disaccharidases
Fructose GlucoseGalactose
Fructose GlucoseGalactose
H2O H2O
Short-Chain Fatty AcidsShort-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 AdaptationsSCFA and Functional Adaptations
Brush bordermembrane
Basolateralmembrane
Fructose GlucoseGalactose
GlucoseGalactose
Na+
Na+
Na+
K+
Fructose
SGLT-1
GLUT5
Na+
K+ ATPase
GLUT2
Sucrase-Isomaltase
glucose uptake
Fructose GlucoseGalactose
Fructose GlucoseGalactose
H2O H2O
What are Dietary Reference Intakes (DRI)?
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 DRIDetermining 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
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
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
Carbohydrate DRI Values for Adults
Function Age Males RDA/AI g/d
Females*RDA/AI g/d
AMDR (% total energy)
Primary energy source for brain, source of calories to maintain body weight
19-30y
130 130 45-65
31-50y
130 130 45-65
50-70y
130 130 45-65
>70y 130 130 45-65
*Recommendations change for pregnant or lactating women
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