chapter 6 脂肪 英文版 营养学.docx
- 文档编号:2404574
- 上传时间:2022-10-29
- 格式:DOCX
- 页数:26
- 大小:1.18MB
chapter 6 脂肪 英文版 营养学.docx
《chapter 6 脂肪 英文版 营养学.docx》由会员分享,可在线阅读,更多相关《chapter 6 脂肪 英文版 营养学.docx(26页珍藏版)》请在冰豆网上搜索。
chapter6脂肪英文版营养学
LipidBasics
Idon'thaveanycleversongparodiesthisweek.:
(Iknow,it'sdisappointing.Maybeyoucanmakeoneupandpostitintheforums?
Ourfabulousandexcitingtopicthisweekislipids!
Sotasty,andsoabused.Let'sstartwiththebasics,asusual.
Technicallyspeaking,therearethreetypesofmoleculesthatfallunderthecategoryof"lipids."Theseare triglycerides, phospholipids,and sterols.It'sprettyeasytoseethatbothtriglyceridesandphospholipidshavefattyacidandglycerolcomponents...butwhataboutsterols?
Theirchemicalstructurelookscompletelydifferent.Evenso,theonethingthatallthreehaveincommonistheirhydrophobicnature,andthisisthebasisoftheircategorizationaslipids.
AsIjustmentioned,bothphospholipidsandtriglycerideshavefattyacidcomponents,solet'stakeacloserlookattheseforamoment. Each fattyacid hasamethylgroup ononeendanda carboxylgroup ontheother.Theseareconnectedbya"carbonbackbone."Thisbackbonecanbejustafewormanycarbonsinlength.Thefattyacidsinfoodsmostcommonlycontainanevennumberofcarbonsintheirchains,andthisisimportantbecauseit'sthecarbonbackbonethatultimatelydeterminestheconsistencyandthetasteofthefat.
Therearetwofeaturesofthecarbonbackbonethatmostinfluenceit'sconsistency.Thefirstisthe length ofthecarbonbackbone.Ifthefattyacidhas2-4carbons,it'sconsideredtobea"short-chain"fattyacid.Ifithas6-10,it'sa"medium-chain"andifithas12ormorecarbonsit'sa"long-chain"fattyacid.Theshorterthefattyacid,themorelikelyitistobeliquidatroomtemperature;conversely,thelongerthefattyacid,themorelikelyitistobesolidatroomtemperature.
Thesecondmajorfactoraffectingconsistencyisthesaturationofthecarbonchain.Rememberfromchemistryclassthatcarboniscapableofmakingfourbonds.Whenallthecarbonsinafattyacidchainareallmakingfourbondseach,thefattyacidissaturated.Ifanyofthecarbonsinthechainaremakingadoublebonds,though,thenthatfattyacidisunsaturated.Ifthere'sjustonedoublebond,it'sa monounsaturated fat,whiletwoormoredoublebondsmakeafattyacid polyunsaturated.Asfarasconsistencygoes,themoresaturatedafattyacidis,themorelikelyitistobesolidatroomtemperature.Fattyacidsthatarepolyunsaturatedaremorelikelytobeliquid.Attheendoftheday,boththelengthandsaturationofthechaininfluencehowliquidorsolidthefatis.Scientistsgobackandforthrepeatedlybetweenmono-versuspolyunsaturatedasfaraswhichtypeoffatisthe"healthiest"toincludeinourdiets.Currentthinkingisthatoncewefulfilourminimumneedforpolyunsaturatedfat(discussedinthenextsection)it'sbesttogettherestofourfatfrommonounsaturatedsources.Weshouldminimizetheamountofsaturatedfatsinourdietasmuchaspossible.
It'sonlyunsaturatedfatsthatcanbe essential.Saturatedfats,whileextemelyimportant,arenotessentialbyournutritiondefinition-yourbodyhastheabilitytomakeallitneedssothere'snoneedforyoutogettheminyourdiet.Ifafatisunsaturated,wecanlookat thepositionofthefirstdoublebond inordertofigureoutwhetherit'sanessentialfattyacidornot.Whenmakingthedetermination,wenumberthemethylcarbonas"carbon#1."Iknow,Iknow,thisdoesnotfollowtherulesyouweretaughtinorganicchemistry.Idon'tknowwhyit'sdonethiswayforfattyacids,butitis.Ifitmakesyoufeelbetteratall,themethylcarbonisalsocalledthe"omegacarbon."Fromcarbon#1wecountdownthechaintothefirstcarboninvolvedinadoublebond.Ifthisendsupbeingbeforetheninthcarboninthechain,it'sanessentialfattyacid(a.k.a.essentialfat).
Checkoutthepolyunsaturatedfattyacidinthepicture,above.Noticethatthefirstdoublebondoccursatcarbonnumbersix.Thisisan omega-6 fattyacid!
Themostcommonexampleofanomega-6fattyacidislinoleicacid.Ontheotherhand,ifthefirstdoublebondwereatcarbonnumberthree,itwouldbean omega-3 fattyacid.Theomega-3'sthatyou'llhearthemostaboutarealpha-linolenicacid,docosahexaenoicacid(DHA)andeicosapentaenoicacid(EPA).Now,althoughhumansdoneedtoobtaintheseessentialfattyacidsinourdiet,itdoesn'ttakemuch-theaverageadultneedsonly2-4tablespoonsofplantoilseachdaytofulfilltherequirement.Fattyfishlikesalmon,halibut,whitefish,etc.arealsoagreatsource-aslongasthey'rebakedorbroiledandnotdeep-fried.
Theomega-3andomega-6fattyacidshavesomevitalbiologicalroles.Mostimportantly,theyaretheprecursorstomoleculescalled eicosanoids.Iknowyourtextbookgoesintosomeprettygorydetailaboutthevariouseicosanoidsandtheirfunctions.However,forourpurposes,Iwouldbethrilled
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- chapter 脂肪 英文版 营养学 英文