NS 315 Unit 3: Carbohydrate Digestion and Absorption Jeanette Andrade MS,RD,LDN,CDE Kaplan University

Objectives DefinitionsDefinitions Dietary CarbohydratesDietary Carbohydrates Digestion/absorption of carbohydratesDigestion/absorption of carbohydrates Glycemic IndexGlycemic Index Glycemic LoadGlycemic Load Case StudyCase Study

Definitions Carbohydrates: mainly comprised of sugars and starchesCarbohydrates: mainly comprised of sugars and starches Sucrase: Splits sucrose into glucose and fructoseSucrase: Splits sucrose into glucose and fructose Lactase: Splits lactose into glucose and galactoseLactase: Splits lactose into glucose and galactose Amylase: Enzyme produced in the pancreas and salivary glands that helps in the digestion of starchesAmylase: Enzyme produced in the pancreas and salivary glands that helps in the digestion of starches Glycolysis: anaerobic catabolism of glucose (more about this in Unit 4)Glycolysis: anaerobic catabolism of glucose (more about this in Unit 4)

Definitions Dextrins: various polysaccharides obtained from starch by the application of heat or acids and used mainly as adhesives and thickening agentsDextrins: various polysaccharides obtained from starch by the application of heat or acids and used mainly as adhesives and thickening agents Glycogen: Highly branched polysaccharide of glucose chains stored primarily in liver and muscle to be used as energyGlycogen: Highly branched polysaccharide of glucose chains stored primarily in liver and muscle to be used as energy Glycogenolysis: The hydrolysis of glycogen to glucose in the liver or muscle to provide energyGlycogenolysis: The hydrolysis of glycogen to glucose in the liver or muscle to provide energy Glyconeogenesis: The synthesis of glucose from molecules that are not carbohydrates: amino acids and fats. During times when the liver is limited in glycogen stores.Glyconeogenesis: The synthesis of glucose from molecules that are not carbohydrates: amino acids and fats. During times when the liver is limited in glycogen stores.

Definitions 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: Monosaccharides Single Sugars- Glucose, Fructose, Galactose What are some foods that contain these saccharides? C 6 H Share same molecular formula: C 6 H

Dietary Carbohydrates: Disaccharides 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: Polysaccharides 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?

Amylose and Amylopectin

Dietary Fiber Dietary FiberDietary 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 3 rd ed)

Digestion of Carbohydrates What enzymes aid in breaking down carbohydrates? What organs aid in breaking down carbohydrates?

Digestion 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, & Distribution 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 Carbohydrates Transporter Major Sites of Expression Characteristics SGLUT 1 Intestinal mucosaIntestinal mucosa, kidney tubules Co-transports one molecule of glucose or galactose along with two sodium ions. Does not transport fructose. GLUT-1 Brain, erythrocyte, endothelial cells, fetal tissues Transports glucose (high affinity) and galactose, not fructose. Expressed in many cells. GLUT-2 Liver, 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.pancreatic beta cells GLUT-3 Brain, placenta and testes Transports glucose (high affinity) and galactose, not fructose. The primary glucose transporter for neurons. GLUT-4 Skeletal and cardiac muscle, adipocytes The insulin-responsive glucose transporter. High affinity for glucose.insulin-responsive GLUT-5 Small intestine, sperm Transports fructose, but not glucose or galactose. Present also in brain, kidney, adipocytes and muscle.

Glycemic Index Why may this be important? What problems do you think happen with the glycemic index?

Carbohydrates- Case Study After 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.