NS 315NS 315Unit 3: Carbohydrate Digestion Unit 3: Carbohydrate Digestion

and Absorptionand Absorption

Jeanette Andrade MS,RD,LDN,CDE

Kaplan University

ObjectivesObjectives

• DefinitionsDefinitions

• Dietary CarbohydratesDietary Carbohydrates

• Digestion/absorption of carbohydratesDigestion/absorption of carbohydrates

• Glycemic IndexGlycemic Index

• Glycemic LoadGlycemic Load

• Case StudyCase Study

DefinitionsDefinitions• CarbohydratesCarbohydrates:: mainly comprised of sugars and mainly comprised of sugars and

starchesstarches

• Sucrase:Sucrase: Splits sucrose into glucose and Splits sucrose into glucose and fructosefructose

• Lactase:Lactase: Splits lactose into glucose and Splits lactose into glucose and galactosegalactose

• Amylase:Amylase: Enzyme produced in the pancreas and Enzyme produced in the pancreas and salivary glands that helps in the digestion of salivary glands that helps in the digestion of starchesstarches

• Glycolysis:Glycolysis: anaerobic catabolism of glucose anaerobic catabolism of glucose (more about this in Unit 4)(more about this in Unit 4)

DefinitionsDefinitions• Dextrins:Dextrins: various polysaccharides obtained from starch by various polysaccharides obtained from starch by

the application of heat or acids and used mainly as the application of heat or acids and used mainly as adhesives and thickening agentsadhesives and thickening agents

• Glycogen:Glycogen: Highly branched polysaccharide of glucose Highly branched polysaccharide of glucose chains stored primarily in liver and muscle to be used as chains stored primarily in liver and muscle to be used as energy energy

• Glycogenolysis:Glycogenolysis: The hydrolysis of glycogen to glucose in The hydrolysis of glycogen to glucose in the liver or muscle to provide energythe liver or muscle to provide energy

• Glyconeogenesis:Glyconeogenesis: The synthesis of glucose from The synthesis of glucose from molecules that are not carbohydrates: amino acids and molecules that are not carbohydrates: amino acids and fats. During times when the liver is limited in glycogen fats. During times when the liver is limited in glycogen stores.stores.

DefinitionsDefinitions• Glycemic Index:Glycemic Index: an indicator of the ability of

foods that contain carbohydrates to raise blood glucose levels within 2 hours

• Glycemic load:Glycemic load: provide the ranking of the food taking into the account the amount of carbohydrate consumed.

GI

100 x grams Carbs consumed

Dietary Carbohydrates:Dietary Carbohydrates:MonosaccharidesMonosaccharides

• Single Sugars- Glucose, Fructose, Galactose• What are some foods that contain these

saccharides?

• Share same molecular formula: CC66HH12120066

Dietary Carbohydrates:Dietary Carbohydrates:DisaccharidesDisaccharides

• Two monosaccharides linked together formed a glycosidic bond (loss of 1 H and 1 OH group)

• 3 main disaccharides:

– Sucrose: glucose + fructose

– Lactose: glucose + galactose

– Maltose: glucose + glucose

Sucrose

What foods do we see these

saccharides in?

Dietary Carbohydrates:Dietary Carbohydrates:PolysaccharidesPolysaccharides

• Polymers of glucosePolymers of glucose– Amylose: linear, unbranched chains of several glucose

molecules. Forms a colloidal dispersion in hot water (swelling the granules to digest within bodies).

• What foods do we see amylose in?

– Amylopectin: highly branched chains of several glucose molecules. Insoluble when digested, but specialized enzymes take the big branches in small maltodextrose type chains.

• What foods do we see amylopectin in?

http://www.chemie.uni-regensburg.de/Organische_Chemie/Didaktik/Keusch/Grafik/amylo-e.gif

Amylose and AmylopectinAmylose and Amylopectin

Dietary FiberDietary Fiber• Dietary Fiber Dietary Fiber is generally defined as “plant

polysaccharides and lignin which are resistant to hydrolysis by the digestive enzymes of man.” – Cellulose– Pectin– Lignin– Gums– Other (Advanced Nutrition and Human Metabolism 3rd ed)

Digestion of CarbohydratesDigestion of Carbohydrates

• What enzymes aid in breaking down carbohydrates?

• What organs aid in breaking down carbohydrates?

Digestion of CarbohydratesDigestion of Carbohydrates• After eating starches, amylase is produced from the

salivary glands and begins breaking down the compound to maltose, maltotriose and α- dextrins

• This digestion process then continues throughout the stomach into the small intestine

• Products of α-amylase are then hydrolyzed into their respective monosaccharides by enzymes located on the brush border of enterocytes. Amylase free in the small intestine is produced by the pancreas. Other enzymes that aid in digestion are maltase, isomaltase, lactase and sucrase.

Absorption, Transport, & Absorption, Transport, & DistributionDistribution

• Absorption of glucose & galactose– Into cell: active transport - SGLT1– Into blood: diffusion, GLUT2

• Absorption of fructose– Into cell: facilitated transport - GLUT5– Into blood: GLUT2– Limited in 60% of adults

Cengage-Wadsworth, 2009

Absorption of CarbohydratesAbsorption of CarbohydratesTransporter

Major Sitesof Expression

Characteristics

SGLUT 1 Intestinal mucosa, kidney tubulesCo-transports one molecule of glucose or

galactose along with two sodium ions. Does not transport fructose.

GLUT-1Brain, erythrocyte, endothelial

cells, fetal tissuesTransports glucose (high affinity) and galactose,

not fructose. Expressed in many cells.

GLUT-2Liver, pancreatic beta cell, small

intestine, kidney.

Transports glucose, galactose and fructose. A low affinity, high capacity glucose transporter; serves as a "glucose sensor" in pancreatic beta cells.

GLUT-3 Brain, placenta and testesTransports glucose (high affinity) and galactose,

not fructose. The primary glucose transporter for neurons.

GLUT-4Skeletal and cardiac muscle,

adipocytesThe insulin-responsive glucose transporter. High

affinity for glucose.

GLUT-5 Small intestine, spermTransports fructose, but not glucose or galactose.

Present also in brain, kidney, adipocytes and muscle.

http://www.vivo.colostate.edu/hbooks/molecules/hexose_xport.html

Glycemic IndexGlycemic Index• Why may this be important?

• What problems do you think happen with the glycemic index?

Carbohydrates- Case StudyCarbohydrates- Case StudyAfter consuming milk, Bob starts to experience bloating, cramping, and increased gas production. However, when Bob consumes yogurt he does not experience any pain.

1. What is wrong with Bob (What is the name of the condition)?

2. What causes this condition?

3. Why did consuming yogurt not cause the same effects as milk?

4. As a nutritionist, what other products or food sources would you recommend to replace milk or alleviate the symptoms?

5. What nutrients may be inadequate in the diet if dairy products are not consumed?

6. Do you have any problems with consuming milk like Bob? Feel free to share any additional information with the class.