HUN1201 LECTURE NOTES CHAPTER 4 Carbohydrates Plant Derived Energy Nutrients What are Carbohydrates Macronutrient Major source of energy for all cells Carbon Hydrogen Oxygen CHO Good sources fruits vegetables grains Glucose The most abundant carbohydrate Produced by plants through photosynthesis Simple carbohydrates Contain one or two molecules Commonly referred to as sugars Monosaccharides contain one molecule Glucose fructose and galactose Disaccharides contain two molecules Lactose maltose and sucrose Complex carbohydrates Oligosaccharides contain 3 to 10 monosaccharides Most polysaccharides consist of hundreds to thousands of glucose molecules Starch glycogen most fibers Complex Carbohydrates Starch Plants store carbohydrates as starch Amylose straight chain of glucose Amylopectin branched chain of glucose Resistant starch fiber glucose molecules linked by beta bonds are largely indigestible Sources grains legumes fruits vegetables Glycogen Not found in food and therefore not a source of dietary Storage form of glucose for animals humans carbohydrate Stored in the liver and muscles Long polysaccharide chains Fiber Dietary fibers are non digestible parts of plants Functional fibers are non digestible forms of carbohydrates extracted from plants and have known health benefits Total fiber Dietary fiber Functional fiber Soluble fibers Dissolve in water viscous and gel forming Associated with risk reduction of cardiovascular disease and type 2 Fermentable digested by intestinal bacteria diabetes Examples pectin gum mucilage Found in citrus fruits berries oats beans Insoluble fibers Not water soluble nonviscous Cannot be fermented by bacteria in the colon Promote regular bowel movements alleviate constipation and reduce diverticulosis Examples lignins cellulose hemicelluloses Good sources whole grains seeds legumes fruits and vegetables Carbohydrate Digestion Salivary amylase Enzyme that begins carbohydrate digestion in the mouth Breaks carbohydrates down to maltose Carbohydrate digestion does not occur in the stomach Stomach acids inactivate salivary amylase Most chemical digestion of carbohydrates occurs in the small intestine Pancreatic amylase Enzyme produced in the pancreas and secreted into the small intestine Digests carbohydrates to maltose Additional enzymes in the microvilli digest disaccharides to monosaccharides Maltase Sucrase Lactase Monosaccharides are absorbed into the cells lining the small intestine and then enter the bloodstream All monosaccharides are converted to glucose by the liver Glucose circulating in the blood is our primary energy source Excess glucose is stored as glycogen in the liver and muscles We do not have the enzymes necessary to digest fiber Bacteria in the large intestine can break down some fiber Most fiber remains undigested and is excreted in the feces Blood Glucose Regulation Blood glucose must be closely regulated Hormones control blood glucose levels Insulin Glucagon Epinephrine Norepinephrine Growth hormone Cortisol Insulin Glucagon Secreted by beta cells of the pancreas Stimulates glucose transporters carrier proteins to help take glucose from the blood across the cell membrane Stimulates the liver to take up glucose and convert it to glycogen Secreted by alpha cells of the pancreas Stimulates the liver to convert glycogen to glucose Stimulates gluconeogenesis the production of glucose from amino acids Epinephrine and Norepinephrine Secreted by the adrenal glands and nerve endings when blood glucose is low Increase glycogen breakdown in the liver releasing glucose into the blood Responsible for our fight or flight reactions to danger Blood Glucose Regulation Growth hormone Secreted by the adrenal glands to act on the liver muscle and adipose tissue Cortisol increase gluconeogenesis decrease muscle glucose use Decrease muscle glucose uptake Increase fatty acid mobilization Increase liver glucose output A food s potential to raise blood glucose Foods with a high glycemic index cause a sudden surge in blood glucose Increase insulin Decrease blood glucose Foods with a low glycemic index cause low to moderate fluctuations in blood glucose Not always easy to predict Food s absorption rate varies with type of carbohydrate preparation methods and its fat and fiber content Most foods are eaten in combination in a meal Glycemic Load Determines the effect of a food on a person s glucose response Grams of carbohydrates in a food are multiplied by the glycemic index Glycemic index and glycemic load remain controversial Evidence of health benefits is weak Value of Lower Glycemic Index Less fluctuations in blood glucose Risk reduction for heart disease and colon cancer High fiber intake helps to improve fat levels in the blood higher HDL and lower LDL Foods with lower glycemic index Beans fresh vegetables whole wheat The role of carbohydrates Energy Red blood cells use only glucose for energy Both carbohydrates and fats supply energy for daily activities Glucose is especially important for energy during exercise Ketosis Fat breakdown during fasting forms ketones Excess ketones increase blood acidity and cause ketoacidosis Sufficient energy from carbohydrates prevents ketone production as alternate energy source Carbohydrates Spare Protein Gluconeogenesis occurs when a diet is deficient in carbohydrate The body will make its own glucose from protein Amino acids from these proteins cannot be used to make new cells repair tissue damage support the immune system or perform any of their other functions Complex Carbohydrates Have Health Benefits Fiber May reduce the risk of colon cancer Helps prevent hemorrhoids constipation and other intestinal problems May reduce the risk of diverticulosis May reduce the risk of heart disease May enhance weight loss May lower the risk of type 2 diabetes How much carbohydrate RDA 130 grams day to supply adequate glucose to the brain AMDR 45 to 65 of daily calories Focus on fiber rich carbohydrate foods Simple Carbohydrates Diets high in simple sugars Can cause tooth decay May increase bad cholesterol May decrease good cholesterol May contribute to obesity Complex Carbohydrates Most Americans eat too little complex carbohydrates Enriched foods nutrients are lost during processing and have been added back so the food meets a specified standard Fortified foods have nutrients added that did not originally exist in the food or existed in insignificant amounts Adequate Intake AI for fiber 25 g per day for women 38 g per day
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