Carbohydrates and the glycaemic index - Better Health Channel

The glycaemic index (GI) SkiptomaincontentHealthyeatingHomeHealthyeatingCarbohydratesandtheglycaemicindexActionsforthispageListen Print SummaryReadthefullfactsheetTheglycaemicindex(GI)ratescarbohydratesaccordingtohowquicklytheyraisetheglucoseleveloftheblood. Theglycaemicload(GL)ratescarbohydratesaccordingtotheglycaemicindexandtheamountofcarbohydrateinthefood.AlowGIratingofafooddoesnotmeanyoucaneatalargerserveofthatfood–thetotalamountofcarbohydrateandkilojouleseatenisstillimportant. OnthispageDigestingandabsorbingcarbohydratesTheglycaemicindex(GI)GlycaemicLoad(GL)GIandexerciseUsingtheGIasaguidetohealthyeatingChoosingbetweenhighandlowGIfoodsWheretogethelpFoodsanddrinksprovideourbodywithenergyintheformofcarbohydrates,fat,proteinandalcohol.Carbohydratesarethebody’spreferredenergysource.Theglycaemicindex(GI)isawaythatcarbohydratesinfoodsanddrinksarerankedaccordingtohowquicklytheyraisetheglucoseleveloftheblood(alsoknownas‘bloodsugarlevel’).Ithasreplacedclassifyingcarbohydratesaseither‘simple’or‘complex’.Foodswithcarbohydratesincludebread,breakfastcereals,rice,pasta,legumes,corn,potato,fruit,milk,yoghurt,sugar,biscuits,cakesandlollies.DigestingandabsorbingcarbohydratesThedigestivesystembreaksdowncarbohydratesinfoodsanddrinksintosimplesugars,mainlyglucose.Forexample,bothriceandsoftdrinkwillbebrokendowntosimplesugarsinyourdigestivesystem.Thissimplesugaristhencarriedtoyourbody’scellsthroughthebloodstream.Thepancreassecretesahormonecalledinsulin,whichhelpstheglucosetomovefromyourbloodintothecells.Onceinsideacell,theglucoseis‘burned’alongwithoxygentoproduceenergy.Ourbrain,musclesandnervoussystemallrelyonglucoseastheirmainfueltomakeenergy.Thebodyconvertsexcessglucosefromfoodintoglycogen.Glycogenactsasastorageformofglucosewithinthemuscletissueandtheliver.Itsroleistosupplementbloodglucoselevelsiftheydropbetweenmeals(especiallyovernight)orduringphysicalactivity.Theglycaemicindex(GI)Theglycaemicindex(GI)isawayofrankingcarbohydrate-containingfoodsbasedonhowslowlyorquicklytheyaredigestedandincreasebloodglucoselevelsoveraperiodoftime–usuallytwohours.TheGIusesglucoseorwhitebreadasareferencefood–ithasaGIscoreof100.Carbohydrate-containingfoodsarethencomparedwiththisreferencetoassigntheirGI.Thisensuresallfoodscomparedhavethesameamountofcarbohydrate,gramforgram.Carbohydratesthatbreakdownquicklyduringdigestionhaveahigherglycaemicindex.ThesehighGIcarbohydrates,suchasabakedpotato,releasetheirglucoseintothebloodquickly.Carbohydratesthatbreakdownslowly,suchasoats,releaseglucosegraduallyintothebloodstream.Theyhavelowglycaemicindexes.Thebloodglucoseresponseisslowerandflatter.LowGIfoodsprolongdigestionduetotheirslowbreakdownandmayhelpwithfeelingfull.GIscaleexamplesTheterms‘lowGI’,‘mediumGI’and‘highGI’aregiventofoodsthatfallwithindifferentrangesoftheGI. Theseranges,alongwithsomeexamplefoods,include:lowGI(lessthan55)–examplesincludesoyproducts,beans,fruit,milk,pasta,grainybread,porridge(oats)andlentilsmediumGI(55to70)–examplesincludeorangejuice,honey,basmatiriceandwholemealbreadhighGI(greaterthan70)–examplesincludepotatoes,whitebreadandshort-grainrice.FactorsthataffecttheGIofafoodFactorssuchasthesize,texture,viscosity(internalfrictionor‘thickness’)andripenessofafoodaffectitsGI.Forinstance,althoughbothripeandunripebananashavealowGI(lessthan55),anunripebananamayhaveaGIof30,whilearipebananahasaGIof51. Fat,protein,solublefibre,fructose(acarbohydratefoundinfruitandhoney)andlactose(thecarbohydrateinmilk)alsogenerallylowerafood’sglycaemicresponse.Fatandacidfoods(likevinegar,lemonjuiceoracidicfruit)slowtherateatwhichthestomachemptiesandslowtherateofdigestion,resultinginalowerGI.Otherfactorspresentinfood,suchasphytates(usedtostorephosphorusinplants)inwholegrainbreadsandcereals,mayalsodelayafood’sabsorptionandlowertheGI.CookingandprocessingcanalsoaffecttheGI–foodthatisbrokendownintofineorsmallerparticleswillbemoreeasilyabsorbedandsohasahigherGI.Foodsthathavebeencookedandallowedtocool(potatoes,forexample)canhavealowerGIwheneatencoldthanwhenhot(forexample,potatosaladcomparedwithhotbakedpotato).HighGIfoodsareinfluencedbylowGIfoodsGenerally,eatinglowGIfoodsandhighGIfoodsatthesametimehastheeffectof‘averaging’theGI.Thisisimportant,asmostfoodsareeatenaspartofamealandthisaffectstheGIvalueoffoods.Forexample,eatingcornflakes(ahigherGIfood)withmilk(alowerGIfood)willreducetheoveralleffectofthecornflakesandmilkmealonbloodglucoselevels.GIsymbolandclaimsonpackagedfoodsYoumighthavenoticedthatsomepackagedfoodproductshaveaGIsymbolormakeclaimsaboutthefood’sGIanditshealtheffects(forexample,‘lowGItohelpyoustayfullerforlonger’).Theseareexamplesofnutritioncontentclaimsandgenerallevelhealthclaims,allowedbyFoodStandardsAustraliaNewZealandunderStandard1.2.7Nutrition,healthandrelatedclaims.TheLowGISymbolandclaimsabouttherelationshipofalowGIproductanditseffectonhealthisonlyavailabletopackagedfoodproductsthatmeetstrictnutritionalandtestingcriteria. Thislabellingisnotcompulsoryforfoodcompaniestofollow,sonotallproductsthatareeligiblewilldisplaythesymbolormakeaclaim.Thisisoftenthecaseforsmallercompanieswhomaynothavethemoneytogothroughthenecessaryprocessestobegiventhelabel.Theseclaimsalsowon’tgenerallybeusedonfoodproductsthatwouldbeeligiblebutarenottypicallypackaged(forexample,freshfruitandvegetables).GlycaemicLoad(GL)Theamountofthecarbohydrate-containingfoodyoueataffectsyourbloodglucoselevels.Forexample,eventhoughpastahasalowGI,alargeservingcanstillcausethebloodglucoselevelstorisemorerapidlythanasmallerserving.Thisiswhatiscalledtheglycaemicload(GL). TheGLbuildsonGI,asitconsidersboththeGIofthefoodandtheamountofcarbohydrateinaportion.GLisbasedontheideathatahighGIfoodconsumedinsmallquantitieswouldgivethesameeffectonbloodglucoselevelsaslargerquantitiesofalowGIfood.GLcanbecalculatedeasilyifyouknowwhatthefood’sGIisandhowmuchcarbohydrateispresentintheserving. CalculatingGlycaemicLoad(GL)TheGLcalculationis:GIxtheamountofcarbohydrates(ingrams)inaservingoffood)÷100.Usingapastaexample:GIofastandardwhitewheatpasta,boiledtoaldentetexture=43Thecarbohydratecontentofastandard180gserve=44gGL=43x44/100=19gHowever,ifahalfportionofpastawaseaten,theGLwouldalsohalve:GIofastandardwhitewheatpasta,boiledtoaldentetexture=43Thecarbohydratecontentofahalfportion90gserve=22gGL=43x22/100=9.5gHereisanotherexample,wherebothfoodscontainthesameamountofcarbohydratebuttheirGIsaredifferent:Asmallbakedpotato(GI=80,carbohydrate=15g)GL=80x15/100=12gAnapple(GI=40,carbohydrate=15g)GL=40x15/100=6gBoththesmallbakedpotatoandtheapplehavethesameamountofcarbohydrate(15g).However,becausetheirGIsdiffer(theappleislowwhilethebakedpotatoishigh),theirGLsalsodiffer,whichmeansthebakedpotatowillcausethebloodglucoselevelofthepersoneatingittorisemorequicklythantheapple. TheUniversityofSydney’sGIsearchshowstheGI,GLandcarbohydratecontentperservingofawidevarietyoffoods.GIandexerciseEatinglowGIfoodstwohoursbeforeenduranceevents,suchaslong-distancerunning,mayimproveexercisecapacity.It’sthoughtthatthemealwillhaveleftyourstomachbeforeyoustarttheevent,butremainsinyoursmallintestinereleasingenergyforafewhoursafterwards.ModeratetohighGIfoodsmaybemostbeneficialduringthefirst24hoursofrecoveryafteraneventtorapidlyreplenishmusclefuelstores(glycogen).UsingtheGIasaguidetohealthyeatingTheGIcanbeconsideredwhenchoosingfoodsanddrinksconsistentwiththeAustralianGuidetoHealthyEating,buttherearelimitations.Forexample,theGIofsomeeverydayfoodssuchasfruits,vegetablesandcerealscanbehigherthanfoodstobeeatenoccasionally(discretionary)likebiscuitsandcakes.Thisdoesnotmeanweshouldreplacefruit,vegetablesandcerealswithdiscretionarychoices,becausethefirstarerichinimportantnutrientsandantioxidantsandthediscretionaryfoodsarenot. GIcanbeausefulconceptinmakinggoodfoodsubstitutionchoices,suchashavingoatsinsteadofcornflakes,oreatinggrainybreadinsteadofwhitebread.Usually,choosingthewholegrainorhigherfibreoptionwillalsomeanyouarechoosingthelowerGIoption.It’snotalwayspossibleornecessarytochoosealllowGIfoods.ThereisroominahealthydietformoderatetohighGIfoods,andmanyofthesefoodscanprovideimportantsourcesofnutrients.Remember,bycombiningalowGIfoodwithahighGIfood,youwillgetanintermediateGIforthatmeal.ChoosingbetweenhighandlowGIfoodsThebestcarbohydratefoodtoeatvariesdependingonthepersonandsituation.Forexample,peoplewithtype2diabetesorimpairedglucosetolerancehavebecomeresistanttotheactionofinsulinorcannotproduceinsulinrapidlyenoughtomatchthereleaseofglucoseintothebloodaftereatingcarbohydrate-containingfoods.Thismeanstheirbloodglucoselevelsmayriseabovethelevelconsideredoptimal.Nowconsidertwocommonbreakfastfoods–cornflakesandporridgemadefromwholegrainoats.Therateatwhichporridgeandcornflakesarebrokendowntoglucoseisdifferent.Porridgeisdigestedtosimplesugarsmuchmoreslowlythancornflakes,sothebodyhasachancetorespondwithproductionofinsulin,andtheriseinbloodglucoselevelsisless. Forthisreason,porridgeisabetterchoiceofbreakfastcerealthancornflakesforpeoplewithtype2diabetes.Itwillalsoprovidemoresustainedenergyforpeoplewithoutdiabetes.Ontheotherhand,highGIfoodscanbebeneficialatreplenishingglycogeninthemusclesafterstrenuousexercise.HighGIcanalsoquicklyrestorebloodglucoselevelstonormalwhensomeonewithdiabetesisexperiencinga‘hypo’,whichiswhentheirbloodglucoselevelsfallbelowthenormalrangeof4–8mmol/L.Forexample,eatingfivejellybeanswillhelptoraisebloodglucoselevelsquickly.Apersonwithdiabetesisonlyatriskofa‘hypo’iftakingcertainmedicationsorinjectinginsulin. Ifyouhaveamedicalcondition,suchasdiabetes,it’simportanttogetadvicefromyourdoctororspecialistbeforemakinganychangestoyourdiet.WheretogethelpYourdoctorDietitiansAssociationofAustralia,Tel.1800812942orvisitvisit FindanAccreditedPractisingDietitianpagetofindadietitiannearyou.DiabetesVictoriaTel.1300437386TheGlycemicIndex,2019,TheUniversityofSydney. AustraliaNewZealandFoodStandardsCode–Standard1.2.7–Nutrition,healthandrelatedclaims,2018,FoodStandardsAustraliaNewZealand. SacksFM,CareyVJ,AndersonCAM,MillerER,CopelandT,CharlestonJetal2014,Effectsofhighvslowglycemicindexofdietarycarbohydrateoncardiovasculardiseaseriskfactorsandinsulinsensitivity–TheOmniCarbrandomizedclinicaltrial,JournaloftheAmericanMedicalAssociation,vol.312,no.23,pp.2531–2541. EsfahaniA,WongJM,MirrahimiA,VillaCr,KendallCW2011,Theapplicationoftheglycemicindexandglycemicloadinweightloss:Areviewoftheclinicalevidence,IUBMBLife,vol.63,no.1,pp.7–13. BurdonCA,SpronkI,ChengHL,O'ConnorHT2017,effectofglycemicindexofapre-exercisemealonenduranceexerciseperformance:asystematicreviewandmeta-analysis,SportsMedicine,vol.47,no.6,pp.1087–1101. 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