NTR 213 Chapter 4 Notes
NTR 213 Chapter 4 Notes NTR 213
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This 7 page Class Notes was uploaded by bjwall on Monday September 19, 2016. The Class Notes belongs to NTR 213 at University of North Carolina - Greensboro taught by Dr. Seth Armah in Fall 2016. Since its upload, it has received 7 views. For similar materials see Introduction to Nutrition in Nutrition at University of North Carolina - Greensboro.
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Date Created: 09/19/16
Chapter 4 – Carbohydrates: Sugars, Starches, and Fibers 4.1 Carbohydrates in Our Food Unrefined foods – foods eaten either just as they are found in nature of with only minimal processing, such as cooking (corn, until it is refined through grinding, cooking, and drying to end up as cornflakes) Refined – foods that have undergone processing that changes or removes various components of the original food o Increased consumption of refined CHO implicated as one of the causes of the current obesity epidemic and rising incidence of chronic diseases o Healthy diet – select more unrefined sources; whole grains, veggies and fruits, and not candies, cookies and sweetened beverages What is a Whole Grain? When you eat a bowl of oatmeal or a slice of whole-wheat toast, you are consuming a whole-grain product. o Include the entire kernel of the grain: the germ, bran, and endosperm o Refined grain products only contain the endosperm Endosperm – largest part of kernel, made up of starch, contains kernels protein Bran – outermost layer, contain most of the fiber and good source of many vitamins and minerals Germ – base of kernel, embryo where sprouting occurs, source of oil and is rich in vitamin E Refined grains sold in US are required to be enriched to make up some of these losses Enrichment – addition to food of specific amounts of nutrients to replace those lost during processing Foods made with refined grains contain more of some nutrients and less of others than foods made from whole grains What is Added Refined Sugar? Account for almost 15% of the calories consumed in the typical American diet Contribute empty calories to the diet because when refined from their plant sources, lose all good things 4.2 Types of Carbohydrates Chemically, CHO are group of compounds made up of one or more sugar units that contain C as well as H and O in the same 2-to-1 proportion found in water. Sugar Unit – sugar molecule that cannot be broken down to yield other sugars Monosaccharide – CHO made up of a single sugar unit Disaccharide – CHO made up of 2 sugar units Polysaccharide – CHO made up of many sugar units linked together Simple Carbohydrates Monosaccharides and disaccharides are classified as simple carbohydrates and are what we commonly refer to as sugars. o 3 most common monosaccharides: Glucose – 6-Carbon monosaccharide that is the primary form of CHO used to provide energy in the body; most important; blood sugar Fructose (fruits & veggies) Galactose (milk sugar) Each contains 6 C, 12 H, 6 O, differ in arrangement of atoms o 3 most common disaccharides: Maltose (formed when starch is digested, chew bread) – 2 glucose Sucrose (table sugar) – glucose & fructose Lactose (milk sugar found in milk & ice cream) – galactose & glucose Complex Carbohydrates Complex Carbohydrates are polysaccharides that are generally not sweet tasting the way simple CHO are. They include glycogen in animals and starches and fibers in plants. o Glycogen – storage form of CHO in animals, made up of many glucose molecules linked together in a highly branched structure Found in liver & muscles, don’t consume it in our diet because the glycogen in animal muscles is broken down soon after animal is slaughtered o Starch – CHO found in plants, made up of many glucose molecules linked in straight or branched chains Storage form of CHO in plants and provides energy for plant growth and reproduction. When we eat plants, we consume the energy stored in the starch. o Fiber is type of complex CHO that cannot be broken down by human digestive enzymes, cannot be absorbed in small intestine and passes to large intestine Contains several chemical substances, some of which are soluble in water Soluble Fiber – fiber that dissolves in water or absorbs water and is readily broken down by intestinal microflora. It includes pectins, gums, and some hemicelluloses (beans, oats, apples, seaweed) o Bacteria in large intestine can break this down Oligosaccharide – CHO made up of 3 to 10 sugar units o Pass to large intestine, digested by bacteria creating gas Insoluble Fiber – fiber that does not dissolve in water and is less readily broken down by bacteria in the large intestine. Includes cellulose, some hemicellulose, and lignin. o Insoluble fiber comes from structural parts of plants – cell walls Adds bulk to fecal matter because becomes relatively unchanged through GI tract (wheat, rye bran, broccoli, celery) 4.3 Carbohydrate Digestion and Absorption Disaccharides and complex CHO must be digested to monosaccharides before they can be absorbed into body. Once absorbed, travel in blood to liver. Carbohydrate Digestion Begins in mouth, but most starch digestion and breakdown of disaccharides occur in small intestine. CHO that cannot be digested pass to colon, some broken down by bacteria, and those that cannot be are excreted into feces. Lactose Intolerance Disaccharide lactose is broken down by enzyme lactase in small intestine. Lactose Intolerance – inability to completely digest lactose due to a reduction in the levels of the enzyme lactase o when consume milk & dairy, lactose passes into large intestine, where it draws in water and is metabolized by bacteria, producing gas and causing abdominal distension, cramping, and diarrhea. Indigestible Carbohydrates Resistance Starch – starch that escapes digestion in the small intestine of healthy people o Not digested b/c natural structure of the grain protects the starch molecules or because cooking and processing alter their digestibility. Legumes, unripe bananas, and cold cooked potatoes, rice, and pasta Indigestible CHO pass through GI tract, slow rate at which nutrients, such as glucose, are absorbed. Fiber also can bind to certain minerals, preventing their absorption. Also speed transit through intestine by increasing the amount of water and the volume of material in the intestine, stimulate peristalsis helping prevent constipation o Fiber promotes health by slowing digestion & absorption, reducing transit time, increasing stool weight, and promoting the growth of healthy microflora. Carbohydrate Absorption Glycemic Response – the rate, magnitude, and duration of the rise in blood glucose that occurs after food is consumed o How quickly and how high blood glucose levels rise are affected by how long it takes a food to leave the stomach and by how fast the food is digested and the glucose is absorbed. Refined sugars and starches cause greater GR than unrefined CHO because sugars and starches consumed alone leave stomach quickly and are rapidly digested and absorbed (sugary soda blood glucose increases within minutes) 4.4 Carbohydrate Functions Main function of CHO is to provide energy Other functions: o Nerve tissue needs galactose o Breast-feeding women – galactose combines with glucose to produce the milk sugar lactose o Oligosaccharides – cell membranes, help signal info about cells o Large polysaccharides – CT provide cushioning and lubrication Getting Enough Glucose to Cells In order to provide a steady supply of glucose, the concentration of glucose in the blood is regulated by the liver and by hormones secreted by the pancreas. Insulin – a hormone made in the pancreas that allows glucose to enter cells and stimulates the synthesis of protein, fat, and liver and muscle glycogen o Lowers the level of glucose in the blood o Overall effect of insulin is to remove glucose from the blood and promote energy storage Glucagon – a hormone made in the pancreas that raises blood glucose levels by stimulating the breakdown of liver glycogen and the synthesis of glucose o Raises blood glucose by signaling liver cells to breakdown glycogen into glucose, same time signals liver to synthesize new glucose molecules Glucose as a Source of Energy Cellular respiration uses O to convert glucose to carbon dioxide and water and provide energy in the form of ATP Glycolysis – anaerobic metabolic pathway that splits glucose into 2 3-C pyruvate molecules; the energy released from 1 glucose molecule is used to make 2 ATP molecules Anaerobic Metabolism – metabolism in the absence of O Aerobic Metabolism – metabolism in the presence of O. It can completely break down glucose to yield CO2, H2O, and ATP o 36 ATP, 18 times more than glycolysis Limited CHO interferes with fat breakdown Most of energy in body is stored as fat 2 fatty acids are broken down into 2-C units that form acetyl-CoA Ketone or Ketone Body – acidic molecule formed when there is not sufficient CHO to breakdown acetyl-CoA o Heart, muscle, kidney can use ketones for energy Ketosis – high levels of ketones in the blood o Starvation, low-CHO diet, untreated diabetes 4.5 Carbohydrates in Health and Disease Diabetes Diabetes Mellitus – disease characterized by elevated blood glucose due to either insufficient production of insulin or decreased sensitivity of cells to insulin o Leading cause of blindness and account for 44% of new cases of kidney failure and more than 60% of nontraumatic lower-limb amputations Types of Diabetes Type 1 Diabetes – form of diabetes caused by autoimmune destruction of insulin-producing cells in the pancreas, usually leading to absolute insulin deficiency Autoimmune Disease – disease that results from immune reactions that destroy normal body cells This form of diabetes accounts for 5-10% of diagnosed cases and usually develops before age 30 No insulin, must inject insulin in order to keep blood glucose levels in normal range When insulin low, the lack of glucose inside cells leads to ketone formation. o In uncontrolled type 1, ketone levels can get high enough to increase acidity of blood, called diabetic ketoacidosis. Type 2 Diabetes – characterized by insulin resistance and relative insulin deficiency, more common form of diabetes o Doesn’t produce enough insulin o Body cells lose sensitivity to insulin – insulin resistance o Genetic and lifestyle factors, adulthood Progressive disease, it usually begins with prediabetes, a condition in which glucose levels are above normal but not high enough to be diagnosed Gestational Diabetes – elevation of blood sugar that is first recognized during pregnancy Hypoglycemia Hypoglycemia – abnormally low blood glucose levels Occurs most frequently in people who have diabetes as a result of overmedication Also occur people without diabetes – abnormalities in insulin production or by way body responds to insulin or other hormones Fasting hypoglycemia occurs when an individual has not eaten, often related to some underlying condition, such as excess alcohol, hormonal deficiencies, or tumors Reactive hypoglycemia occurs in response to the consumption of high-CHO foods Dental Caries Dental caries, or cavities, are best-documented health problem associated with CHO intake. 85% of people 18 & older have had caries Occur when bacteria in mouth form colonies, known as plaque, on the tooth surface. Not brushed or flossed away, bacteria metabolize CHO from food we eat, producing acids. Acids dissolve tooth enamel and the underlying tooth structure, forming dental caries. o Sucrose most cariogenic b/c is it easily metabolized to acid by bacteria Weight Management CHO and Weight Loss Type of CHO you eat can affect how hungry you feel and whether you lose or gain weight o High in refined – rapid rise in glucose, insulin promotes fat storage, weight gain Pros and Cons of nonnutritive sweeteners One way to reduce amount of refined sugar in diet is to replace sugar with nonnutritive sweeteners (also artificial sweeteners). Foods high in added sugar tend to be nutrient poor, replacing them with these does not increase nutrient density of diet or improve overall diet quality Heart Disease Diets high in fiber reduce heart disease risk by helping to lower blood cholesterol, reduce blood pressure, normalize blood glucose levels, and prevent obesity Bowel Health Fiber and other indigestible CHO add bulk and absorb water in the GI tract, making feces larger and softer and reducing pressure needed for defication. o This helps reduce the incidence of constipation and hemorrhoids, the swelling of veins in the rectal or anal area. o Reduces risk of developing outpouches in wall of colon called diverticula Fecal matter can accumulate in these pouches, causing irritation, pain, and inflammation, condition called diverticulitis May lead to infection 4.6 Meeting Carbohydrate Needs 2 main points: getting enough CHO to meet need for glucose and choosing types that promote health and prevent disease Carbohydrate Recommendations RDA is 130 g/day Acceptable Macronutrient Distribution Range is 45-65% of total calorie intake AI 38 g/day for men and 25 g/day for women; typical intake is only 15 g/day MyPlate recommends 6 oz of grains, 2 cups of fruit, 2 ½ cups of veggies for 2000 calorie diet Make half your grains whole, increase your fruits and veggies, and limit added sugars