Y khoa, dược - Chapter 4: Carbohydrates: simple sugars and complex chains

Chapter 4 Carbohydrates: Simple Sugars and Complex ChainsWhat Are Carbohydrates?Sugars, starches, and fibersMajor food sources: PlantsProduced during photosynthesisTwo main carbohydrate typesSimple (Sugars)Complex (Starches and fibers)Simple SugarsMonosaccharidesGlucoseFructoseGalactoseSimple SugarsDisaccharides: Consist of two monosaccharides linked togetherSucroseLactoseMaltoseMonosaccharidesGlucoseMost abundant simple sugar in nature Also called dextroseGives food a mildly sweet flavorUsually joined to another sugar in foodsProvides energy to body cellsBody closely regulates blood sugar levelsMonosaccharidesFructoseAlso called levulose or fruit sugarTastes the sweetest of all the sugarsOccurs naturally in fruits and vegetablesFound in fruits, honey, and corn syrupMonosaccharidesGalactoseRarely occurs as a monosaccharide in foodUsually bonds to glucose to form lactosePrimary sugar in milk and dairy productsDisaccharidesSucrose: glucose + fructose“Table sugar”Made from sugar cane and sugar beetsListed as sugar on food labelsLactose: glucose + galactose“Milk sugar”Found in milk and milk productsDisaccharidesMaltose: glucose + glucose“Malt sugar”Seldom occurs naturally in foodsProduct of starch breakdownFound in germinating cereal grainsComplex CarbohydratesChains of two or more sugar moleculesOligosaccharidesThree to ten sugar moleculesExamples sources: dried beans, peas, and lentilsPolysaccharidesLong chains of monosaccharidesStructural differences affect how they behave in water and with heatingDigestible or nondigestibleComplex CarbohydratesStarchPlants store energy as starchFound in grains, legumes, and tubers (potatoes and yams)Long chains of glucose unitsAmylose—straight chainsAmylopectin—branched chainsResistant starch: A starch that is not digestedComplex CarbohydratesGlycogenLiving animals store carbohydrate in the form of glycogenProvides body glucose when blood glucose levels get lowHighly branched chains of glucose unitsMost stored in our skeletal muscle and liverCarbohydrate “loading”Complex CarbohydratesFiberNondigestible carbohydrates and ligninsDietary fiber: Found in plantsFruits, vegetables, legumes, and whole grainsFunctional fiber: Isolated and added to foodsTotal fiber: Sum of dietary fiber and functional fiberComplex CarbohydratesTypes of fiberCelluloseIndigestible by humans and a component of dietary fiberHemicellulosesVariety of monosaccharides with many branching side chainsPectinsDietary fiber found in all plants, especially fruitsComplex CarbohydratesTypes of fiberGums and cilagesGel-forming fibers that help hold plant cells togetherLigninsIndigestible substances that make up woody parts of vegetables and the seeds of fruitsComplex CarbohydratesTypes of fiberBeta-glucansPolysaccharides of branched glucose unitsFound in barley and oatsHelp decrease blood cholesterol levelsChitin and chitosanPrimarily consumed in supplement formMarketed as weight-loss supplementsMay impair absorption of fat-soluble vitamins and some mineralsCarbohydrate Digestion and AbsorptionDigestion breaks down carbohydrates to single sugarsMouthSalivary amylase begins digestion of carbohydratesStomachAcidity of stomach juices halt action of salivary amylase and stops carbohydrate digestionCarbohydrate Digestion and AbsorptionDigestionSmall intestinePancreatic amylase continues starch digestionBrush border enzymes digest disaccharidesOther digestive enzymesMaltase, sucrase, and lactase split maltose, sucrose, and lactose, respectivelyCarbohydrate Digestion and AbsorptionDigestionBonds that link glucose moleculesAlpha bondsBroken down by human enzymesStarchBeta bondsBonds remain unbroken by human enzymesCelluloseCarbohydrate Digestion and AbsorptionDigestionEnzymesHighly specificExamples include lactase and BeanoSome carbohydrates remain intact, such as fiber and resistant starchCarbohydrate Digestion and AbsorptionAbsorption: The small intestine swings into actionEnd products of carbohydrate digestionGlucoseGalactose  glucoseFructose  glucoseLiverStores and releases glucose as need to maintain blood glucose levelsCarbohydrates and Glucose in the BodyGlucose is our primary fuelNeeded to burn fat efficientlyWhen we eat food, our bodiesImmediately use some glucose to maintain normal blood glucose levelsStore excess glucose as glyocgen in liver and muscle tissueCarbohydrates and Glucose in the BodyUsing glucose for energyLiver glycogenMaintains normal blood glucose levelsMuscle glycogenFuels muscle activityCarbohydrates and Glucose in the BodySparing body proteinAdequate carbohydrates prevent body from making glucose from body proteinsPreventing ketosisKetone bodies  ketosis  dehydrationBody needs a minimum of 50 to 100 grams of carbohydrate/day to prevent ketosisCarbohydrates and Glucose in the BodyRegulating blood glucoseTo maintain an adequate supply for cellsControlled by hormonesInsulinKey “unlocking” body cells and allowing glucose to enter and fuel themGlucagonBreaks down glycogen to glucoseEpinephrine“Fight-or-flight” hormoneCarbohydrates and Glucose in the BodyRegulating blood glucoseGlycemic indexFoods vary in their effect on blood glucose levelsIndex measures the effect of food on blood glucose levelsThe Role of Carbohydrates in Our DietRecommended Carbohydrate IntakeRDA = 130 grams per dayDietary Guidelines“Reduce the intake of added sugars”AMDR for added sugars = ½ of all grains as whole grainsThe Role of Carbohydrates in Our DietCurrent Consumption: How much are we eating?AMDR = 45–65% of kcalAverage American adult = 49–50% of kcal13% of population has added sugar intake > 25% of kcalHigh soft drink consumptionMilk consumption and vitamin and mineral quality of diet is decliningThe Role of Carbohydrates in Our DietChoosing Carbohydrates WiselyIncrease fruit, vegetables, whole grains, low-fat milkStrategiesEat peel fruit/vegetablesEat legumesChoose brown riceChoose high-fiber cerealDrink plenty of water!The Role of Carbohydrates in Our DietHigh intake of foods rich in dietary fiber offers many health benefits, including reduced risk ofObesityType 2 diabetesCardiovascular diseaseGastrointestinal disordersIncrease fiber intake gradually while drinking plenty of fluidsCarbohydrates and HealthFiber and obesityPossible role in weight controlFiber and type 2 diabetesBetter control of blood glucoseFiber and cardiovascular diseaseCan lower blood cholesterol levelsFiber and gastrointestinal disordersHealthier gastrointestinal functioningCarbohydrates and HealthNegative effects of excess fiberGradual intake and increased water consumptionCan bind small amounts of mineralsCarbohydrates and HealthModerating sugar intakeUse less added sugarLimit soft drinks, sugary cereals, candy, ice cream, and sweet dessertsChoose fresh fruits or those canned in water or juiceCarbohydrates and HealthNutritive sweetenersMonosaccharides, disaccharides, and sugar alcoholsNatural vs. refinedNon-nutritive sweetenersSaccharinAspartameAcesulfame KSucraloseCarbohydrates and HealthSugar and dental caries promoted by:Carbohydrate remaining in the mouthFood that sticks to teethFrequent consumptionSip high sugar drinks over time