哈医大精品课程营养与食品卫生学第一章营养学基础2

第一章营养学基础碳水化合物CarbohydratesMaincontentsDefinitionofcarbohydratesClassificationofcarbohydratesDigestion&absorptionofCHOFunctionsofcarbohydratesDisordersrelatedtoCHOmetabolismDietaryreferenceintakesofCHOsCarbohydratesareoneofthethreemacronutrienttypesthatprovideenergytoourbodies.Carbohydratescontaincarbon,hydrogen,andoxygen.碳水化合物：属三大能量营养素之一，主要由碳、氢、氧构成。一、碳水化合物的定义Whatarecarbohydrates?Carbohydratecanbeabbreviatedas“CHO”.Weobtainedcarbohydratespredominantlyfromplantfoodssuchasfruits,vegetables,andgrain.Why?PlantsmakecarbohydratesthroughtheprocessofphotosynthesisEnergyfromsunCarbondioxidefromairGlucosestoredinplantWaterWater+CarbondioxideGlucose光合作用二、碳水化合物的分类ClassificationofcarbohydratesCarbohydratesSimpleComplexDisaccharidesMonosaccharidePolysaccharidesOligosaccharide寡糖单糖双糖多糖HOHCH2OHHOHOHHOHHHGlucoseOHOHHOHHOHCH2OHCH2OHFructoseHOOHOHOHHHHHCH2OHGalactoseThethreemostcommonmonosaccharides.ALLofthemcontainidenticalatoms……StructureofmonosaccharidesMonosaccharides-Glucose（葡萄糖）Glucoseisthemostabundantsugarmoleculefoundinourdietsandinourfoods.Glucosedoesnotgenerallyoccurbyitselfinfoodsbutattachestoothersugarstoformdisaccharidesandcomplexcarbohydrates.Inourbodies,glucoseisthepreferredsourceofenergyforthebrain.食物中最多的单糖，但不以单独形式存在，常与其他糖形成双糖或多糖的形式存在，葡萄糖优先为大脑提供能量。Monosaccharides-Fructose（果糖）Fructoseisalsocalledfruitsugar.Fructoseisthesweetestnaturalsugar,occursnaturallyinfruitsandvegetables.PrefixMonosaccharides-Galactose（半乳糖）Galactosedoesnotoccuraloneinfoods.Itjoinswithglucosetocreatelactose,oneofthedisaccharides.Sweetestmonosaccharides?Themostabundantmonosaccharides?Thesweetest：fructoseThemostabundant：glucoseDisaccharide（双糖）Disaccharide:Acarbohydratecompoundconsistingoftwosugarmoleculesjoinedtogether.Thethreemostcommondisaccharidesfoundinfoodsarelactose（乳糖）,maltose（麦芽糖）,andsucrose（蔗糖）.Disaccharides–Lactose（乳糖）＋GlucoseGalactoseLactoseLactose:Consistofoneglucosemoleculeandonegalactose(半乳糖）molecule.Disaccharides—Maltose（麦芽糖）Maltose:alsocalledmaltsugar,consistoftwomoleculesofglucose.Itdoesnotgenerallyoccurbyitselfinfoods,butresultsasaby-productofdigestion.＋GlucoseDisaccharides—Sucrose（蔗糖）Sucroseiscomposedofoneglucosemoleculeandonefructose（果糖）molecule.＋Sucroseprovidesmuchofthesweettastefoundinhoney,fruits,andvegetables.HowabouttheSucroseandfructose?Sweeterthanlactoseormaltose,why?哪种双糖最甜--麦芽糖，蔗糖，乳糖？麦芽糖--2个葡萄糖蔗糖--1个葡萄糖+1个果糖乳糖--1个葡萄糖+1个半乳糖蔗糖Oligosaccharide（寡糖）Oligosaccharidearecomposedof3to10monosaccharides.Themostcommonoligosaccharidesareraffinose（棉籽糖）andstachyose（水苏糖）.Theycannotbedegradedbyenzymesinthesmallintestine,butcanbebrokedowninthelargeintestine.Polysaccharides（多糖）Polysaccharidesincludestarch（淀粉）,glycogen（糖原）andmostfibers（纤维）.PolysaccharidesStarchGlycogenFiber淀粉糖原纤维Polysaccharide--StarchStarch:Apolysaccharidestoredinplantsandisthestorageformofglucoseinplants.（淀粉是葡萄糖在植物中的贮存形式）Excellentfoodsourcesofstarchinclude?grains(wheat,rice,corn,oats,andbarley),legumes(peas,beans,andlentils),andtubers(potatoesandyams).Ourbodieseasilydigestmoststarches，wecallthemdigestiblestarch(可吸收淀粉）.根据其结构可分为直链淀粉（amylose）和支链淀粉（amylopectin），前者易使食物老化，后者易使食物糊化（gelatinization）。However,somestarchinplantsisnotdigestibleandiscalledresistantstarch（抗性淀粉）.抗性淀粉：指健康者小肠中不吸收的淀粉及其降解产物。Whenourintestinalbacteriatrytodigestresistantstarch,afattyacidcalledbutyrateisproduced.Consumingresistantstarchmaybebeneficialbecausebutyrateissuggestedtoreducetheriskofcancer.豆科食物（Legumes）含有的抗性淀粉比谷类、蔬菜和水果多。BeansproutGreensoybeanGlycogen:Apolysaccharidestoredinanimals,includinghumans.Verylittleglycogenexistsinfood.Thus,glycogenisnotadietarysourceofcarbohydrate.Polysaccharide-Glycogen（糖原）Whichtissuesareabundantinglycogen?Westoreglycogeninourmusclesandliver.Wecanbreakdownglycogenveryquicklyintoglucosewhenweneeditforenergy.Basedonthewatersolubleability,fibercanbeclassifiedintosolublefibersandinsolublefibers.Insolublefibers（不溶性纤维）:cellulose（纤维素）,hemicellulose（半纤维素）andxylogen（木质素）.Solublefibers（可溶性纤维）:果胶（pectin)，树胶和粘胶.Polysaccharide--Fiber膳食纤维（dietaryfiber）：是指植物性食物或原料中糖苷键大于3个，不能被人体小肠消化和吸收，但对人体健康有意义的碳水化合物。膳食纤维包括部分非淀粉多糖（纤维素、半纤维素、木质素、果胶等）、抗性淀粉、葡聚糖以及部分低聚糖等。(1)增强肠道功能、有利粪便排出Helpspreventconstipationandotherintestinalproblemsbykeepingourstoolsmoistandsoft.FunctionsofdietaryfiberDietaryfiberincreasesfaecalbulkthroughwaterbindingbyfiber.Fibergivesgutmuscles“somethingtopush”andmakesiteasiertoeliminatestools.(2)控制体重和减肥Mayenhanceweightloss,aseatingahighfiberdietcausesapersontofeelmorefull.Fiberabsorbswater,expandsinourintestine,andslowsthemovementoffoodthroughtheupperpartofthedigestivetract.(3)降低血糖和血胆固醇DecreasethelevelofbloodsugarandcholesterolMayreducetheriskofheartdiseasebydelayingorblockingtheabsorptionofdietarycholesterolintothebloodstream.(4)降低结肠癌的发病风险Mayreducetheriskofcoloncancer.Whilethereisstillsomecontroversysurroundingthisissue,manyresearchersbelievethatfiberbindscancer-causingsubstancesandspeedstheireliminationfromthecolon.三、碳水化合物的消化及吸收WehavelearnedmanyformsofCHOscontaininginourfoods,whichoneistheformofenergyusedbyourbodies?TheprimarygoalofCHOdigestionistobreakdownpolysaccharidesanddisaccharidesintomonosaccharidesthatcanbeconvertedtoglucose.Digestionofcarbohydratesinfoods(Inthemouth)CHOdigestionbeginsinthemouth.Question:Whenyoueatsteamedbread（馒头）,noticethatyoucanactuallytasteitbecomingsweeter,Why?Salivaamylase（淀粉酶）breaksstarch(淀粉）intosmallerparticlesandeventuallyintothemaltose（麦芽糖）.Disaccharidesarenotdigestedinthemouth.Inthestomach,alldigestionofCHOsceases.Digestionofcarbohydratesinfoods(Inthestomach)Becausetheacidinthestomachinactivatesmostofthesalivaryamylaseenzyme.Wouldyouguessthereasons?Themajorityofcarbohydratedigestionoccursinthesmallintestine.Digestionofcarbohydratesinfoods(Inthesmallintestine)Pancreaticamylasesecretedbythepancreasintothesmallintestine.Pancreaticamylasecontinuestodigestanyremainingstarchintomaltose（麦芽糖）.Additionalenzymesfoundintheintestinaltractbreakdowndisaccharidesintomonosaccharides.MaltoseSucroseLactoseGlucoseGlucose&FructoseGlucose&GalactoseMaltaseSucraseLactaseAbsorbedbymucosalcellsBloodstream麦芽糖蔗糖乳糖TransformofcarbohydratesintheliverFructose&galactoseGlucoseCellEnergyGlycogenBloodvesselsBloodvesselsExcessglucosecanbetransformedandstoredasglycogeninliverandmuscles.Ourlivercanstore70g(or280calories)ofglycogen.Ourmusclescannormallystoreabout120g(or480cal)ofglycogen.TransformofcarbohydratesintheliverLiverglycogen：maintainsbloodglucoselevels,providetheneedsofourcells,includingthoseofourbrain,spinalcordandredbloodcell.Inaddition,Itprovideenergytothemusclesduringintenseexercise（剧烈运动）.Wedonotpossessenzymesthatcanbreakdownfiber.Thus,fiberpassesthroughthesmallintestineundigestedandentersthelargeintestineorcolon.Thereisnoanydigestedprocessforfiber。Onceintothelargeintestine,bacteriabreakdownsomeundigestedcarbohydrates,causingtheproductionofgasandafewfattyacids（产酸、产气）.Digestionofcarbohydratesinfoods(Inthelargeintestine)Thecellsofthelargeintestineusethesefattyacidsforenergy.Thefiberremaininginthecolonaddsbulktoourstoolsandisexcretedinfeces.Salivaryamylasebreaksdownstarchintoshorterpolysaccharidesandafewmaltose.NodigestiontakesplacePancreaticamylaseissecretedintosmallintestine.Majorityofstarchweredigested.Pancreaticamylase…Specificenzymes…；Allmonosaccharidesareabsorbedbysmallintestineandenterbloodstream.Monosaccharidestraveltoliverinbloodstream,thentocellstoprovideenergy;Excessglucoseisstoredasglycogeninliver.BacteriabreakdownsomeundigestedCHO;remainingfiberisexcretedinfeces.Summary四、碳水化合物的功能Functionofcarbohydrates1.提供和贮存能量（provideandstoreenergy）Howmuch？4kcal/g.Someofourcellscanalsousefatandevenproteinforenergyifnecessary.However,ourredbloodcellscanutilizeonlyglucoseandourbrain&othernervoustissuesprimarilyrelyonglucose.CarbohydrateFatAmountsofcarbohydrateandfatusedduringthedifferentextentofexercise.LightModerateIntense67%45%13%87%55%33%PercentcontributiontototalenergyFatbreakdownisaslowprocessandrequireoxygenwecanbreakdownglucoseveryquicklyeitherwithorwithoutoxygen.Functionofcarbohydrates2.节约蛋白质作用(CHOsspareproteins)定义：当摄入足够的碳水化合物时，可以防止体内和膳食中的蛋白质转变为葡萄糖.糖异生(gluconeogenesis)Gluconeogenesis:Thegenerationofglucosefromthebreakdownofproteinintoaminoacids.Whenourbodyusesproteinsforenergy,theaminoacidsfromtheseproteinscannotbeusedtomakenewcells,repairtissuedamage,supportourimmunesystem,orperformanyoftheirotherfunctions.Usingaminoacidsinthismanneroveraprolongedperiodoftimecancauseserious,possiblyirreversible,damagetotheseorgans.3.抗生酮作用（Preventthegenerationofketones)Ketoacidosis:Aconditioninwhichexcessiveketones（酮体）arepresentintheblood,causingthebloodtobecomeveryacidic,whichaltersbasicbodyfunctionsanddamagestissues.FunctionofcarbohydratesLowcarbohydrateintakecanleadtoketoacidosis(酮症酸中毒）Thus,whencarbohydrateintakeisinadequate,ourbodyseeksanalternativesourceoffuelforthebrainandbeginstobreakdownstoredfat.acetyl-CoAisthemetabolitesoffattyacidoxidation.Ifinadequatecarbohydrateintakecontinuesforanextendedperiodoftime,excessacetyl-CoAcanbeconvertedtoketones.Thehighacidityofthebloodinterfereswithbasicbodyfunctions,causesthelossofleanbodymass,anddamagesmanybodytissues.Wheredoketonescomefrom?4.机体的构成成分5.改变食物的色、香、味、型6.提供膳食纤维Functionsofcarbohydrates五、碳水化合物代谢相关疾病糖尿病低血糖症乳糖不耐症Glucosemoleculesaretoolargetocrossthecellmembranesofourtissuesindependently.Togetin,glucoseneedsassistancefromthehormoneinsulin.血糖的调节过程GlucoseinbloodenterscellsInsulinstimulatesglucosetransportintocellInsulinsecretedbypancreasentersbloodstreamTissuecellmembraneWhenbloodglucoseishigh……GlucagonsecretedbypancreasentersbloodstreamGlucagonstimulatesglycogenbreakdownGlucoseissecretedintobloodstreamandtransportedtocellsLivercellmembraneWhenbloodglucoseislow……胰高血糖素Normally,insulinandglucagonbalanceeachothertomaintainbloodglucosewithinahealthyrange.Ifthisbalanceisaltered,itcanleadtohealthconditionssuchasdiabetes（糖尿病）orhypoglycemia（低血糖症）.血糖指数（Glycemicindex，GI）定义：50g含碳水化合物的食物血糖应答曲线下面积与同一个体摄入50g碳水化合物的 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 食物（葡萄糖或面包）血糖应答曲线下面积之比。血糖指数是食物升高血糖潜力的一个参考指标，反应了食物对血糖的影响程度。高GI食物能使血糖突然升高。血糖指数的应用指导合理膳食，有效控制血糖糖尿病人低血糖症患者、运动员有助于控制体重改善胃肠道功能Lactoseintolerance:Adisorderinwhichthebodydoesnotproducesufficientlactaseenzyme（乳糖酶）andthereforecannotdigestfoodsthatcontainlactose,suchascow’smilk.乳糖不耐症（Lactoseintolerance）主要症状：胃肠不适、胀气、痉挛和腹泻等。Itisestimatedthatupto70%oftheworld’sadultpopulationsufferthisdisorder.Noteveryoneexperienceslactoseintolerancetothesameextent(smallamounts,nottolerantany)LactoseintoleranceLactoseintoleranceshouldnotbeconfusedwithamilkallergy.Peoplewhoareallergictomilkexperienceanimmunereactiontotheproteinsfoundincow’smilk.六、膳食参考摄入量Dietaryreferenceintakes中国营养学会推荐我国居民的碳水化合物的膳食推荐摄入量占总能量的55%～65%。食物GI食物GI食物GI大米饭88柚子25熟香蕉52酸奶83鲜桃28猕猴桃52牛奶27.6梨36芒果55鲜豆腐31.9苹果36菠萝66生香蕉30柑43西瓜72小结碳水化合物的分类及功能膳食纤维的定义及功能乳糖不耐症