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