2009 Cengage - Wadsworth. Carbohydrates

Transcription

1 Carbohydrates

2 The Chemist s View of Carbohydrates Carbohydrates are made of carbon, hydrogen and oxygen atoms. These atoms form chemical bonds that follow the laws of nature. The chemical formula for carbohydrates are similar, C n (H 2 O) n In other words, for every carbon, there is a molecule of water, hence the name carbo-hydrates or hydrated carbons

3 Common Carbohydrates in Human Nutrition Sucrose (table sugar) Lactose (milk sugar) Maltose Oligo/ Polysaccharides; Starch and Glycogen Fiber glucose glucose Glucose Glucose Soluble (fermentable) fructose Galactose Glucose Insoluble

4 Two Monosaccharides: Glucose and Fructose

5 Two Monosaccharides: Glucose & Galactose

6 The Simple Carbohydrates Disaccharides Maltose consists of two glucose units. It is produced during the germination of seeds and fermentation. Sucrose is fructose and glucose combined. It is refined from sugarcane and sugar beets, tastes sweet, and is readily available. Lactose is galactose and glucose combined. It is found in milk and milk products.

7 The Complex Carbohydrates Few (oligo-) or many (poly-) saccharides Multiple glucose units linked together in straight or branched chains. Glycogen (carbohydrate storage in animals) Storage form of glucose in the body Provides a rapid release of energy when needed Starches Storage form of glucose in plants Found in grains, tubers, and legumes

8 The Complex Carbohydrates Dietary fibers provide structure in plants, are very diverse, and cannot be broken down by human enzymes. Soluble fibers are viscous and can be digested by intestinal bacteria (fermentable). These fibers are found in fruits and vegetables. Insoluble fibers are nonviscous and are not digested by intestinal bacteria. These fibers are found in grains and vegetables.

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10 The Complex Carbohydrates Fiber Sources Dietary fibers are found in plant foods. Functional fibers are health-benefiting fibers that are added to foods or supplements. Total fiber considers both dietary and functional fibers. Resistant starch is starch that escapes digestion in the small intestine and that may be fermented in the large intestine.

11 The Complex Carbohydrates Resistant Starch Starches physically inaccessible to digestive enzymes: partly milled grains & seeds Starch resistant to digestion due to the nature of the starch granule: raw potato, unripe banana, some legumes and high amylose starches (e.g., high amylose corn) Starch that forms from retrograded amylose & amylopectin during food processing: e.g. potatoes, bread, cornflakes Starch produced by chemical modification

12 Glucose in the Body Primary role Energy Red blood cells and cells of the nervous system require glucose for energy Other Roles Glycoproteins (e.g. intrinsic factor) Glycolipids 2006 Thomson-Wadsworth

13 Glucose in the Body The body stores glucose as glycogen in liver and muscle cells. The body uses glucose for energy if glycogen stores are available.

14 Glucose in the Body If glycogen stores are depleted, the body makes glucose from protein. Gluconeogenesis is the conversion of protein to glucose. Protein-sparing action is having adequate carbohydrate in the diet to prevent the breakdown of protein for energy. Body fat is metabolized more efficiently when some carbohydrate is available

15 Glucose in the Body In fasting, starvation or situations of carbohydrate depletion, the body can obtain energy by mobilizing fat stores. In the absence of carbohydrate, however this can lead to a condition known as ketosis. The body can use glucose to make body fat when carbohydrates are consumed excessively.

16 Glucose in the Body The Constancy of Blood Glucose The Regulating Hormones Insulin moves glucose into the cells and helps to lower blood sugar levels. Glucagon brings glucose out of storage and raises blood sugar levels. Epinephrine acts quickly to bring glucose out of storage during times of stress. Blood glucose can fall outside the normal range with hypoglycemia or diabetes.

17 Glucose in the Body The Constancy of Blood Glucose Maintaining Glucose Homeostasis Low blood glucose may cause dizziness and weakness. High blood glucose may cause fatigue. Extreme fluctuations can be fatal. Normal blood glucose levels (fasting) mg/dl

18 Maintaining Blood Glucose Homeostasis

19 Glucose in the Body Diabetes Type 1 diabetes is the less common type with no insulin produced by the body. Type 2 diabetes is the more common type where fat cells resist insulin. Prediabetes is blood glucose that is higher than normal but below the diagnosis of diabetes. Hypoglycemia is low blood glucose and can often be controlled by dietary changes.

20 Health Effects and Recommended Intakes of Sugars Dental caries Caused by bacteria residing in dental plaque Bacteria ferment the sugars from food and the breakdown of starches in the mouth, producing an acid that erodes tooth enamel Factors involved Length of time sugars are in contact with the teeth. Stickiness of the sugar-containing food

21 Health Effects and Recommended Intakes of Sugars Excessive sugar intake can contribute to the development of body fat by adding to excess kcalorie intake. Sugar may be able to alter blood lipid levels and contribute to heart disease in some. E.g. a high intake of simple carbohydrates is associated with elevations of blood triglycerides

22 Health Effects and Recommended Intakes of Sugars Excessive intakes of sugar may displace nutrients and contribute to obesity. Natural does not always mean nutritious. (e.g., honey) Foods with added sugars are part of discretionary kcalories Foods with added sugars have sugars listed as a first ingredient. Naturally occurring sugars from fruits, vegetables and milk are acceptable sources.

23 Health Effects and Recommended Intakes of Sugars There is no scientific evidence that sugar causes misbehavior in children and criminal behavior in adults. Sugar consumption per se does not cause diabetes.

24 Health Effects and Recommended Intakes of Sugars Recommended Intakes of Sugars The USDA Food Guide states that added sugars can be included in the diet as part of discretionary kcalories. Dietary Guidelines for Americans 2010: Limit SoFAS (Solid Fats and Added Sugars) DRI suggest added sugars should contribute no more than 25% of a day s total energy intake.

25 Look for these ingredients as added sugars on food labels Brown sugar Corn sweetener Corn syrup Dextrose Fructose Fruit juice concentrate Glucose High-fructose corn syrup Honey Invert sugar Lactose Maltose Malt syrup Molasses Raw sugar Sucrose Sugar Syrup

26 Health Effects and Recommended Intakes of Starch and Fibers Health Effects of Starch and Fibers May be some protection from heart disease and stroke Soluble fibers bind with and increase excretion of bile. Since bile is made from cholesterol, the body must use its cholesterol stores to make new bile acids. As a result, blood cholesterol levels are decreased. Fiber may also displace fat in the diet.

27 Health Effects and Recommended Intakes of Starch and Fibers Reduce the risk of type 2 diabetes by decreasing glucose absorption Enhance the health of the GI tract which can then block the absorption of unwanted particles May protect against colon cancer by removing potential cancer-causing agents from the body

28 Dietary Fiber Soluble Fiber Oatmeal Oat bran Nuts & seeds Most fruit (e.g., strawberries, blueberries, pear, apples) Dry beans & peas Insoluble Fiber Whole wheat bread Barley Brown rice Couscous Bulgur or whole grain cereals Wheat bran Seeds Most vegetables Fruits

29 Health Effects and Recommended Intakes of Starch and Fibers Promote weight control Complex carbohydrates provide less fat and added sugar. High fiber increases viscosity of GI contents & results in slower transit time (greater time in contact with satiety receptors)

30 Health Effects and Recommended Intakes of Starch and Fibers Recommended Intakes of Starch and Fibers RDA for carbohydrate is 130 g per day AMDR for carbohydrate is 45-65% of total kcalories Dietary Guidelines for Americans 2010 encourage a variety of whole grains, vegetables, fruits and legumes daily.

31 Health Effects and Recommended Intakes of Starch and Fibers Recommended Intakes of Fiber FDA: 25 grams for a 2,000-kcalorie diet. DRI: 14 g per 1000 kcalorie intake (28 grams for a 2,000 kcalorie diet) American Dietetic Association: g per day. World Health Organization suggests no more than 40 g per day.

32 Health Effects and Recommended Intakes of Starch and Fibers Harmful effects of excessive fiber intake Displaces energy and nutrient-dense foods Abdominal discomfort and distention May interfere with nutrient absorption

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34 Comparison of Bread Labels

35 Voluntary Whole Grain Stamps from the Whole Grain Council Whole grain stamp for products offering ½ serving or more of whole grain 100% whole grain stamp for products where ALL of the grain is whole grain