What Are Carbohydrates? Chapter 4 Carbohydrates: Simple Sugars and Complex Chains. Monosaccharides. Simple Sugars 6/17/16. BIOL 103, Spring 2016

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1 What Are Carbohydrates? Chapter 4 Carbohydrates: Simple Sugars and Complex Chains BIOL 103, Spring 2016 Sugars, starches, and fibers Major food sources: Plants Produced during photosynthesis Two main carbohydrate types Simple (Sugars) Complex (Starches and fibers) Monosaccharides Glucose Fructose Galactose Simple Sugars Monosaccharides Glucose/Dextrose Most simple sugar in nature Gives food a mildly sweet flavor Usually joined to another sugar in foods to form disaccharides, starch, dietary fiber Provides energy to body cells Blood sugar levels Only fuel source used by brain 1

2 Monosaccharides Fructose/Levulose Tastes the of all the sugars Occurs naturally in fruits and vegetables Found in fruits, vegetables, honey, and corn syrup High Fructose Corn Syrup Why do we use it? Before 1970s à U.S. cane sugar à too expensive 1980s, food companies switched to cheaper corn Pepsi/Coke switched in 1984 High Fructose Corn Syrup How is it made? 1. Convert glucose à fructose, using isomerase 2. Add corn syrup, then a specific ra\o of glucose Example: HFCS 55 (so_ drinks) Why is High Fructose Corn Syrup associated with weight gain? 1. Corn is cheap à cheaper soda à supersize à drink more à more calories 2. Fructose does NOT release insulin and lep:n à does not feel full à drink more à more calories However, note that overconsump\on of ANY forms of sugar will contribute to weight gain. 2

3 Monosaccharides Galactose Rarely occurs as a monosaccharide in food Usually bonds to glucose to form Simple Sugars Disaccharides: Consist of two monosaccharides linked together Sucrose: Lactose: Maltose: Linked by bonds Disaccharides Sucrose: glucose + fructose Made from sugar cane and sugar beets Listed as sugar on food labels Lactose: glucose + galactose Found in milk and milk products Lactose Intolerance Who has it? Anyone who does not have enough, which normally converts (lactose à glucose + galactose) Why do you get it? Lactase nonpersistence (most common) Injury/infec\on to intes\ne usually during infancy Developmental lactase deficiency in premature infants Congenital lactase deficiency: rare gene\c disorder from birth 3

4 Disaccharides Maltose: glucose + glucose Seldom occurs naturally in foods Product of starch breakdown Found in germina\ng cereal grains Chains of three or more sugar molecules Oligosaccharides 3-10 sugar molecules Examples sources: dried beans, peas, and len\ls Polysaccharides Long chains of monosaccharides Structural differences affect how they behave in water and with hea\ng Diges\ble (e.g. starch) or nondiges\ble (e.g. fiber) Starch Storage form of energy in Found in grains, legumes, and tubers (potatoes and yams) Long chains of glucose units Amylose Amylopec:n Digested more rapidly than amylose Resistant starch: A starch that is not digested 4

5 Glycogen Storage form of carbohydrates in Highly branched chains of glucose units Blood glucose Most stored in our and Carbohydrate loading Fiber Nondiges\ble carbohydrates and lignins Dietary fiber: soluble + insoluble fiber Fruits, vegetables, legumes, and whole grains Func:onal fiber: Isolated and added to foods Total fiber: Sum of dietary fiber and func\onal fiber Types of Dietary Fiber Soluble Insoluble 5

6 (Dietary Fiber) Gums and mucilages Gums: Gel- forming fibers in plant cell walls and seeds Mucilages: gela\nous soluble fiber found in seaweed Pec:ns Sugar acids ; keeps fruits in shape Dietary fiber found in all plants, especially fruits and berries Pec\ns + acid + sugar = jam (Dietary Fiber) Beta- glucans Polysaccharides of branched glucose units linked with beta glycosidic bonds Found in barley and oats Help decrease blood cholesterol levels Lignin: Non actually carbohydrates; composed of mul\- ring alcohol units that compose the only non- carbohydrate component of dietary fiber Found in cell walls of woody plants and the seeds of fruits (Dietary Fiber) Cellulose: long, straight chains of glucose molecules with beta glycosidic bonds Structural func\on in plants: forms the woody fibers in trees and strong plant cell walls Hemicelluloses: variety of monosaccharides with many branching side chains Usually mixed with cellulose in plants Outer bran layer in cereal grains, legumes, vegetables, nuts Dietary Fiber 6

7 Carbohydrate Diges\on Diges\on breaks down carbohydrates to single sugars Mouth Stomach s acidity stops the ac\on of salivary amylase à stops carbohydrate diges\on Diges\on Small intes\ne Carbohydrate Diges\on amylase con\nues starch diges\on enzymes digest disaccharides Other diges\ve enzymes: Maltase, sucrase, and lactase Carbohydrate Diges\on Diges\on Bonds that link glucose molecules Alpha bonds Beta bonds 7

8 Carbohydrate Absorp\on Absorp\on in the small intes\ne Glucose, galactose, fructose molecules travel to the liver through the portal vein converts the absorbed monosaccharaides to : Galactose à glucose Fructose à glucose Carbohydrates and Glucose in the Body Excess glucose is stored as Liver glycogen Muscle glycogen Carbohydrates and Glucose in the Body Glucose is our primary fuel To drive chemical processes To maintain normal blood glucose levels Other sources of energy: fat, protein What is the order of energy usage by body? 8

9 Consequence of Low Blood Sugar Sparing body protein Adequate carbohydrates prevent body from making glucose from body proteins Preven\ng ketosis Ketone bodies à ketosis à dehydra\on Body needs a minimum of 50 to 100 grams of carbohydrate/day to prevent ketosis Carbohydrates and Glucose in the Body Regula\ng blood glucose Hyperglycemia vs. Hypoglycemia Controlled by hormones: Insulin Glucagon Epinephrine (Adrenaline) Fight- or- flight hormone Regula\ng Blood Glucose Glycemic Index measures effect of food on blood levels Different foods vary in their effect on blood glucose levels Foods with High Glycemic Index cause faster and higher rise in blood glucose 9

10 Glycemic Index High Blood Glucose: Diabetes Mellitus What is diabetes? Normally: Eat food with glucose à blood and cells If too much blood glucose à pancreas releases insulin à blood glucose decreases If you have diabetes: Pancreas: liple or no insulin OR cells do not respond appropriately to insulin à hyperglycemia High Blood Glucose: Diabetes Forms of diabetes mellitus: Diabetes Type I: Diabetes Type II: Gesta:onal diabetes: The Role of Carbohydrates in Our Diet Cons: excess simple sugar à weight gain, poor nutrient intake, tooth decay Pros: high intake of foods rich in dietary fiber offers many health benefits, including reduced risk of: Obesity Type 2 diabetes Cardiovascular disease Gastrointes\nal disorders Increase fiber intake gradually while drinking plenty of fluids 10

11 Carbohydrates and Health Fiber and obesity Fiber and type 2 diabetes Fiber and cardiovascular disease Fiber and gastrointes:nal disorders Carbohydrates and Health Nega\ve effects of excess fiber: If add supplemental fiber too quickly, may have side effects: abdominal bloa\ng, gas Can bind small amounts of minerals à prevent some mineral absorp\on Examples: Zinc, Calcium, Iron Fiber does not have UL: because ea\ng a lot of fiber (found naturally in foods) doesn t really affect overall health of healthy people. Carbohydrates and Health Modera\ng sugar intake Use less added sugar Limit so_ drinks, sugary cereals, candy, ice cream, and sweet desserts Choose fresh fruits or those canned in water The Role of Carbohydrates in Our Diet Choosing Carbohydrates Wisely Increase fruit, vegetables, whole grains, low- fat milk Strategies Eat peel fruit/vegetables Eat legumes Choose brown rice Choose high- fiber cereal Drink plenty of water! 11

12 Carbohydrates and Health Nutri:ve sweeteners: Monosaccharides, disaccharides, and sugar alcohols Natural vs. refined Non- nutri:ve sweeteners: Saccharin Aspartame Acesulfame K Sucralose Nutri\ve Sweeteners Nutri:ve Sweeteners: substances that sweeten food and can absorbed and yield energy in the body. Types: 1. Natural: mono + di- saccharides e.g. honey, maple syrup 2. Refined: mono + di- saccharides extracted from plant food e.g. white sugar, fructose 3. Sugar Alcohol/Polyols: may be sugar/sucrose free, but not always calorie free e.g. xylitol Non- Nutri\ve Sweeteners Non- nutri:ve sweeteners: ar\ficial sweeteners ; yields almost no energy Types: 1. Saccharin (1970s; bladder cancer) 2. Aspartame (phenylalanine + aspar\c acid; PKU) 3. Acesulfame K (stable under heat) 4. Sucralose (used in baked goods, beverages, gela\n, etc.) 12