The Carbohydrates: Sugars, Starches, and Fibers PDF

11/7/2023 1 THE CARBOHYDRATES: SUGARS, STARCHES, AND FIBERS Fall 2023 Dr. Hala Nawaiseh 11/7/2023 2 The Chemist’s View of Carbohydrates Carbohydrates Compounds composed of carbon, ox...

11/7/2023 1 THE CARBOHYDRATES: SUGARS, STARCHES, AND FIBERS Fall 2023 Dr. Hala Nawaiseh 11/7/2023 2 The Chemist’s View of Carbohydrates Carbohydrates Compounds composed of carbon, oxygen, and hydrogen arranged as monosaccharides or multiples of monosaccharides. Most, but not all, carbohydrates have a ratio of one carbon molecule to one water molecule: (CH2 O)n. 11/7/2023 3 The Chemist’s View of Carbohydrates The dietary carbohydrate family includes: Monosaccharides: Single sugars Disaccharides: Pairs of monosaccharides Polysaccharides: Chains of monosaccharides Simple carbohydrates: Monosaccharides and disaccharides. Complex carbohydrates: Starches and fibers 11/7/2023 4 The Chemist’s View of Carbohydrates Monosaccharides Carbohydrates of the general formula C n H2nOn that typically form a single ring. The monosaccharides important in nutrition are hexoses, sugars with six atoms of carbon and the formula C6 H12O6. The three monosaccharides most important in nutrition all have the same numbers and kinds of atoms (6 carbon atoms, 12 hydrogens, and 6 oxygens) :Glucose, Galactose, and Fructose. The monosaccharides differ in their arrangements of the atoms. 11/7/2023 5 Monosaccharides Glucose A monosaccharide; sometimes known as blood sugar in the body or dextrose in foods. It serves as an essential energy source for all the body’s activities. Glucose is one of the two sugars in every disaccharide and the unit from which the polysaccharides are made almost exclusively. 11/7/2023 6 Monosaccharides Fructose Monosaccharide; sometimes known as fruit sugar or levulose. Fructose is the sweetest of the sugars. Fructose has exactly the same chemical formula as glucose—C6H12O6—but its structure differs. Fructose occurs naturally in fruits and honey; soft drinks, ready-to-eat cereals, and desserts that have been sweetened with high-fructose corn syrup. 11/7/2023 7 Monosaccharides Galactose A monosaccharide; part of the disaccharide lactose. Occurs naturally in foods as a single sugar only in very small amounts. It has the same numbers and kinds of atoms as glucose and fructose in yet another arrangement. 11/7/2023 8 Disaccharides Disaccharides The disaccharides are pairs of monosaccharides. The three disaccharides most important in nutrition all contain glucose; the second member of the pair is fructose, galactose, or another glucose. These carbohydrates and all the other energy nutrients are put together and taken apart by similar chemical reactions: condensation and hydrolysis. 11/7/2023 9 Disaccharides Maltose A disaccharide composed of two glucose units; sometimes known as malt sugar Consists of two glucose units. Maltose is produced whenever starch breaks down as happens in human beings during carbohydrate digestion. It also occurs during the fermentation process that yields alcohol. Maltose is only a minor constituent of a few foods, most notably barley. 11/7/2023 10 Disaccharides Sucrose A disaccharide composed of glucose and fructose; commonly known as table sugar, beet sugar, or cane sugar. Sucrose also occurs in many fruits and some vegetables and grains. Fructose and glucose together form the disaccharide sucrose. Sucrose is the sweetest of the disaccharides. These sugars account for the natural sweetness of fruits, vegetables, and grains. 11/7/2023 11 Disaccharides Lactose Disaccharide composed of glucose and galactose. Known as milk sugar. Lactose contributes half of the energy (kcalories) provided by fat-free milk. 11/7/2023 12 polysaccharides Polysaccharides Compounds composed of many monosaccharides linked together. An intermediate string of 3 to 10 monosaccharides is an oligosaccharide. Polysaccharides are slightly more complex, containing many glucose units and, in some cases, a few other monosaccharides strung together. 11/7/2023 13 polysaccharides Three types of polysaccharides are important in nutrition: glycogen, starches, and fibers. Glycogen is a storage form of energy in the body; Starch is the storage form of energy in plants; Fibers provide structure in stems, trunks, roots, leaves, and skins of plants. Both glycogen and starch are built of glucose units. Fibers are composed of a variety of monosaccharides and other carbohydrate derivatives. 11/7/2023 14 Polysaccharides 11/7/2023 15 Polysaccharides Glycogen An animal polysaccharide composed of glucose. A storage form of glucose manufactured and stored in the liver and muscles. Glycogen is not a significant food source of carbohydrate and is not counted as a dietary carbohydrate in foods. Found to only a limited extent in meats and not at all in plants. 11/7/2023 16 Polysaccharides Starches: plantpolysaccharides composed of many glucose molecules. Long, branched or unbranched chains of hundreds or thousands of glucose molecules linked together. The human body stores glucose as glycogen, but plant cells store glucose as starch. All starchy foods come from plants. 11/7/2023 17 Polysaccharides Fibers Dietary fibers are the structural parts of plants and thus are found in all plant-derived foods—vegetables, fruits, whole grains, and legumes. Most dietary fibers are polysaccharides. Nonstarch polysaccharides 11/7/2023 18 Polysaccharides Fibers The nonstarch polysaccharide fibers include: cellulose, hemicelluloses, pectins, gums, and mucilages. Fibers also include some nonpolysaccharides such as lignins. Dietary fibers are fermented by bacteria in the colon to short- chain fatty acids, which are absorbed and metabolized by cells in the GI tract and liver. 11/7/2023 19 11/7/2023 20 Digestion and Absorption of Carbohydrates 11/7/2023 21 Carbohydrate Digestion In the Mouth The salivary enzyme amylase starts to work in the mouth, hydrolyzing starch to shorter polysaccharides and to the disaccharide maltose. In the Stomach Carbohydrate digestion ceases in the stomach. The activity of salivary amylase diminishes as the stomach’s acid and protein-digesting enzymes inactivate the enzyme. The stomach’s digestive juices contain no enzymes to break down carbohydrates. Fibers are not digested. 11/7/2023 22 Carbohydrate Digestion In the Small Intestine The small intestine performs most of the work of carbohydrate digestion. A major carbohydrate-digesting enzyme, pancreatic amylase, enters the intestine via the pancreatic duct and continues breaking down the polysaccharides to shorter glucose chains and maltose. The final step takes place on the outer membranes of the intestinal cells. 11/7/2023 23 Carbohydrate Digestion In the Small Intestine There specific enzymes break down specific disaccharides: Maltase breaks maltose into two glucose molecules. Sucrase breaks sucrose into one glucose and one fructose molecule. Lactase breaks lactose into one glucose and one galactose molecule. At this point, all polysaccharides and disaccharides have been broken down to monosaccharides. 11/7/2023 24 Carbohydrate Digestion In the Large Intestine Within 1 to 4 hours after a meal, all the sugars and most of the starches have been digested. Only the nondigestible carbohydrates remain in the digestive tract 11/7/2023 25 11/7/2023 26 11/7/2023 27 The Constancy of Blood Glucose Maintaining Glucose Homeostasis To function optimally, the body must maintain blood glucose within limits that permit the cells to nourish themselves. If blood glucose falls below normal, a person may become dizzy and weak; if it rises above normal, a person may become fatigued. Among the dietary factors that most influence these fluctuations in blood glucose are carbohydrate (quality and quantity), protein, and fiber intakes. 11/7/2023 28 The Constancy of Blood Glucose The Regulating Hormones Blood glucose homeostasis is regulated primarily by two hormones: Insulin, which moves glucose from the blood into the cells. Glucagon, which brings glucose out of storage when needed. 11/7/2023 29 11/7/2023 30 The Constancy of Blood Glucose Balancing within the Normal Range The maintenance of normal blood glucose depends on foods and hormones. When blood glucose falls below normal, food can replenish it, or in the absence of food, glucagon can signal the liver to break down glycogen stores. When blood glucose rises above normal, insulin can signal the cells to take in glucose for energy. Eating balanced meals that provide abundant carbohydrates, including fibers, and a little fat help slow down the digestion and absorption of carbohydrate so that glucose enters the blood gradually. Eating at regular intervals also helps the body maintain a balance between the extremes. 11/7/2023 31 The Constancy of Blood Glucose Falling outside the Normal Range In some people, blood glucose regulation fails. When this happens, either of two conditions can result: diabetes or hypoglycemia. People with these conditions need to plan their diets and physical activities to help maintain their blood glucose within a normal range. Table 4-3 presents the blood glucose levels defining hypoglycemia, normal, prediabetes, and diabetes. 11/7/2023 32 Health Effects of Sugars Obesity and Chronic Diseases High-fructose corn syrup (beverages) is composed of fructose and glucose in a ratio of roughly 50:50. Compared with sucrose, high-fructose corn syrup is less expensive, easier to use, and more soluble. Research findings tend to support an association between consuming sugary beverages and increases in energy intake and body weight. Reducing the consumption of sugar-sweetened beverages or replacing them with beverages such as water or milk can help support a healthy body weight 11/7/2023 33 Health Effects of Sugars Obesity and Chronic Diseases Added sugars in general (fructose) in particular, favor the fat- making pathways and impair the fat-clearing pathways in the liver. The resulting blood lipid profile increases the risk of heart disease. Researchers suggest replacing sugar-sweetened beverages with water. The American Heart Association recommends limiting added sugars to no more than : 100 kcalories/day (women)……5% of 2000 -kcalorie diet. 150 kcalories/per day (men)….. 5% 2500-kcalorie diet. 11/7/2023 34 Recommended Intakes of Sugars Food labels currently list the total grams of sugar a food provides, which reflects both added sugars and those occurring naturally in foods. keep in mind that 1 teaspoon of sugar (white sugar, brown sugar, corn syrup, honey, nectar, jam, jelly, maple syrup, or molasses : Provides 4 grams of carbohydrate and about 20 kcalories per teaspoon. 1 tablespoon of ketchup supplies about 1 teaspoon of sugar. Those who drink soft drinks regularly should keep in mind that a 12-ounce can of soda delivers about 10 teaspoons of sugar. 11/7/2023 35 Recommended Intakes of Sugars The Dietary Reference Intakes (DRI) committee did not publish a Tolerable Upper Intake Level (UL). Dietary Guidelines for Americans urge consumers to limit their daily intake of added sugars to 10 percent of total kcalories. Alternative sweeteners: Artificial sweeteners, Highintensity sweeteners, Sugar alcohols 11/7/2023 36 Health Effects and Recommended Intakes of Starch and Fibers Heart Disease Diets rich in whole grains, legumes, vegetables, and fruits may protect against heart attack and stroke by lowering blood pressure, improving blood lipids, and reducing inflammation. Vegetable proteins, and phytochemicals are associated with a lower risk of heart disease. Oatmeal was one of the first foods recognized for its ability to reduce blood cholesterol and the risk of heart disease. 11/7/2023 37 Health Effects and Recommended Intakes of Starch and Fibers Heart Disease Foods rich in soluble fibers (such as oat bran, barley, and legumes) lower blood cholesterol by binding with bile acids in the GI tract and thereby increasing their excretion. In addition, the bacterial by-products of fiber fermentation in the colon inhibit cholesterol synthesis in the liver. 11/7/2023 38 Health Effects and Recommended Intakes of Starch and Fibers Diabetes High-fiber foods especially whole grains play a key role in managing and preventing type 2 diabetes. When soluble fibers trap nutrients and delay their transit through the GI tract, glucose absorption is slowed, which helps prevent glucose surge and rebound. 11/7/2023 39 Health Effects and Recommended Intakes of Starch and Fibers Cancer The findings support dietary fiber, not fiber supplements or additives, which lack valuable nutrients and phytochemicals that also help protect against cancer. Fibers may help prevent colon cancer by diluting, binding, and rapidly removing potential cancer-causing agents from the colon. Soluble fibers stimulate bacterial fermentation of resistant starch and fiber in the colon, a process that produces short- chain fatty acids that lower the pH. These small fat molecules activate cancer-killing enzymes and inhibit inflammation in the colon. 11/7/2023 40 Health Effects and Recommended Intakes of Starch and Fibers Weight Management Foods rich in fiber tend to be low in solid fats and added sugars and therefore prevent weight gain and promote weight loss by delivering less energy per bite. As fibers absorb water from the digestive juices, they swell, creating feelings of fullness and delaying. 11/7/2023 41 Health Effects and Recommended Intakes of Starch and Fibers Recommended Intakes of Starch and Fibers The DRI suggest that carbohydrates provide about half (45 to 65 percent) of the energy requirement 11/7/2023 42 THE END