Chapter 4 Carbohydrates PDF

4 Carbohydrates  Facts Primary source of energy for the body Least expensive and most abundant of the energy nutrients Named for the chemical elements they are composed of—carbon, hydrogen, and oxygen 4-0...

4 Carbohydrates  Facts Primary source of energy for the body Least expensive and most abundant of the energy nutrients Named for the chemical elements they are composed of—carbon, hydrogen, and oxygen 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Functions Provide energy Protein-sparing (action-cuts out from carbs and add fats from diet) Normal fat metabolism Provide fiber 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Providing Energy Each gram of carbohydrate provides 4 calories. A body needs a constant energy supply. A half day’s supply of carbohydrates is stored in the liver and muscles for use as needed. Stored form is called glycogen. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Protein-Sparing Action The primary function (additional of proteins fats from diets) is to build and repair tissues. When enough carbohydrates (at least 50–100 g/day) are ingested, proteins are spared to be used for their primary function. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Normal Fat Metabolism Without an adequate supply of carbohydrates, fat is metabolized to meet energy requirements. Ketones are produced as a byproduct of fat metabolism. Ketosis may result. “Ketones”-is build up in blood and urine if body fats breaks down fast Ketosis-characterized by raised level of ketone bodies in body tissues 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Providing Fiber Dietary fiber is found in grains, vegetables, and fruits. Recommended intake is 20–35 g/day. Fiber lowers blood glucose levels; may prevent some colon cancers; and helps prevent constipation, hemorrhoids, and diverticular disease by softening stool. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Food Sources Principal sources of carbohydrates are plant foods: Cereal grains Vegetables Fruits Nuts Sugars The only substantial animal source is milk. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Classification Monosaccharides –sugar that cannot split in simple sugar Simple sugars-most basic form in sugar which can easily absorb in blood stream Disaccharides- simple sugar that soluble in water Polysaccharides-form of carbohydrate stored in animal organism Complex carbohydrates- found most common in peas,beans ,whole grain and veggies 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Monosaccharides Simplest form of carbohydrates Absorbed directly into the bloodstream from the small intestine Glucose –simple sugar which an important energy source in living organism Fructose-sugar found in honey and fruit Galactose-milk sugar 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Monosaccharides Glucose Also called dextrose All other forms are converted to glucose for eventual metabolism. Berries, grapes, sweet corn, and corn syrup Central nervous system, red blood cells, and brain use only glucose as fuel. 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Monosaccharides Fructose Also called fruit sugar Ripe fruits, honey, and soft drinks Sweetest of all the monosaccharides Galactose Product of the digestion of milk Not found naturally Source is lactose 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Disaccharides simple sugar soluble in water Pairs of monosaccharides Must be changed to simple sugars by hydrolysis before absorption Sucrose, maltose, and lactose 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Disaccharides Sucrose Composed of glucose and fructose Form of carbohydrate present in granulated, powdered, and brown sugar, and in molasses One of the sweetest and least expensive sugars Sources: sugar cane, sugar beets, maple syrup, candy, jams, and jellies 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Disaccharides Maltose Intermediary product in the hydrolysis of starch Also created during the fermentation process that produces alcohol Found in some infant formulas, malt beverage products, and beer Not as sweet as glucose or sucrose 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Disaccharides Lactose Sugar found in milk Distinct from other sugars in that it is not found in plants Helps body absorb calcium Not as sweet as monosaccharides or other disaccharides 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Polysaccharides (number of sugar molecules bonded together) Complex carbohydrates Compounds of many monosaccharides Important polysaccharides in nutrition Starch Glycogen Fiber 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Polysaccharides Starch Found in grains and vegetables Storage form of glucose in plants Supplies energy over a longer period of time because it takes the body longer to digest polysaccharides than monosaccharides or disaccharides. 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Polysaccharides Glycogen Sometimes called animal starch because it is the storage form of glucose in the body Hormone glucagon helps liver convert glycogen to glucose as needed 4-0 (continues) Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  (continued) Polysaccharides Fiber It is indigestible because it cannot be broken down by digestive enzymes. Insoluble: does not readily dissolve in water (cellulose, hemicellulose, lignins) Soluble: partially dissolves in water (gums, pectins, some hemicellulose, mucilages) 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Sources of Polysaccharides Starch: cereals, grains, potatoes, corn, beans, and yams Glycogen: glucose stored in liver and muscles Cellulose: wheat bran, whole-grain cereals, fruits, green, and leafy vegetables Hemicellulose: whole grains 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Digestion and Absorption: Monosaccharides Simple sugars absorbed directly into the bloodstream Carried to the liver; fructose and galactose changed to glucose Glucose then carried to cells 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Digestion and Absorption: Disaccharides Enzymes sucrase, maltase, and lactase convert sucrose, maltose, and lactose to simple sugar glucose Simple sugars absorbed directly into the bloodstream Glucose carried to cells 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Digestion and Absorption: Polysaccharides More complex; digestibility varies Cellulose wall broken down, starch changed to intermediate product dextrin(thickening agent in food and gums) then maltose, and finally glucose Starch digestion begins in the mouth where the enzyme salivary amylase begins to change starch to dextrin 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Metabolism Islets of Langerhans(cluster of pancreatic cells) in pancreas secrete insulin. Insulin is the hormone that controls glucose metabolism. Impaired or absent insulin secretion results in high blood glucose level (hyperglycemia). Low blood glucose level of < 70 mg/dL (hypoglycemia) may occur with too much insulin or insufficient food intake. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Dietary Requirements Food and Nutrition Board of the National Research Council recommends: Half of one’s energy requirement should come from carbohydrates, preferably complex Weight loss and fatigue can result from a diet deficient in carbohydrates. Severe deficiency can result in ketosis. Surplus become adipose tissue. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.  Conclusion Carbohydrates provide energy. Carbohydrates should be the major source of energy. These nutrients spare protein, maintain normal fat metabolism, and provide fiber. Excessive carbohydrate intake may lead to obesity, dental caries, and digestive disturbances. 4-0 Copyright © 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.