Transcript Carbohydrates - Absorption and Metabolism

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