Casein,Whey,andSoyProteinandTheir

RelativeEffectsonMuscleGrowth

GregoryDonlon

November9,2015

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AbstractProteinsupplementationinthepost-exerciseperiodisknowntostimulatemuscleproteinsynthesis(MPS),leadingtomusclegrowthandstrengthincrease.Therearethreetypesofproteinsourcescommonlyusedasasupplement:whey,soy,andcasein.Dothesedifferentproteinscauseanequalincreaseinmusclegrowth,orisonesuperiortotherest?Thepurposeofthisliteraturereviewwastoevaluatethehypothesisthatwheyproteinissuperiortocaseinandsoy.AstudybyTangetal.measuredtheresponseofMPSafterconsumptionofwhey,soy,andcaseinprotein.Subjectsperformedlegresistanceexercises,consumedoneofthethreeproteinsupplements,andmusclefractionalsyntheticrate(FSR)wasdetermined.TheresultsshowedthatwheyproteinstimulatedthegreatestMPS(P<0.05).Hartmanetal.comparedincreasesofleanmassbetweensubjectsthatconsumedfat-freemilkorasoyproteindrinkpost-exerciseforthedurationofagiventrainingprogram.BodycompositionwasmeasuredusingDXAscansbeforeandafterthetwelve-weekregimen.Subjectsinthemilkgroupshowedasignificantlylargerdecreaseinfatmass(P<0.05)andincreasedstrength(4-10%).AthirdstudybyWilkinsonetal.alsocomparedmilktosoyproteinusingacrossoverdesignwhilefocusingondifferencesinmuscleproteinaccretion.Subjectscompletedtworandomtrialsinwhichtheyconsumedasoyormilkbeverageafterexercise.Bloodandmusclesamplesweretakentodeterminethechangesinfractionalsynthesisratesofmuscleproteins.SubjectsshowedsignificantlygreaterMPS(P<0.05)followingconsumptionofthemilkbeverage.Althoughallthreestudiessuggestthatwheyproteinstimulatesthemostmusclegrowthandstrengthincrease,thereisstillmuchroomforresearchwithmoresubjects,andafocusonspecificgroupsofpeoplesuchasathletes,ormalesversusfemales.

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Introduction

Ascollegiateandprofessionalsportsgetmorecompetitive,sportsprogramscontinuetolookforwaystogivetheirplayersthecompetitiveedgetheyneedtowin.Oneofthesewaysisthroughresistancetrainingandrecoverynutritionthroughproteinsupplementation.Resistancetrainingleadstoimprovedmusclesizeandstrength,whichleadstopowerandperformanceonthefield.Thisiswhyalmosteveryelitesportsteamusesresistancetrainingintheirtrainingregimen.Inordertomaximizeprogressintheweightroom,athletesareoftensupplementedwithproteinofsometype.Wheyproteinismostcommonlyusedinathleticprogramsovercaseinandsoy.Thesethreeproteinsareshowntoproducegreatermuscleproteinsynthesis(MPS)wheningestedfollowingresistancetrainingratherthanjustrelyingonproteininthedietalone(1,2).1,2Asubstantialamountofresearchhasbeendonetodetermineexactlywhichtypeofproteinismostbeneficialformusclegrowthandstrengthgains.Thehypothesisbeingtestedisthatwheyproteinismoreeffectiveatincreasingmusclestrengthandsizethansoyorcaseinduetoitsfastdigestionandsuperiorleucinecontent. Proteinsupplementationfollowingresistancetrainingisknowntostimulatemuscleproteinsynthesis(MPS)leadingtomusclegrowththatcanbeseeninstrengthandsize(3).3Therearethreemaintypesofproteinusedasasupplement:whey,soy,andcasein.Proteinscanbecategorizedbyhowfasttheyaredigestedandabsorbed,andbytheirsource.Wheyandcaseinproteins,forexample,arebothfromdairysourcessuchasmilk.Wheyproteinhoweverisafastdigestingprotein,whilecaseinismuchslower(4).4Regardlessoftheirdigestionspeeds,bothoftheseproteinscontaintheaminoacidsneededformuscleresponsessuchasproteinsynthesisfollowingresistanceexercise(5).5Soyprotein,althoughfromadifferentsource,isdigestedsimilarlytowheymeaningthatitisafasterabsorbingproteinthancasein(6).6 Aminoacidsfromtheseproteinsstimulateamildinsulinresponse,puttingthebodyinananabolicstatewhichallowsfortheriseinproteinsynthesis(7).7Aparticularcategoryofaminoacids,branched-chainaminoacids(BCAAs)areespeciallyimportantcontributorstoMPS.OneBCAAinparticular,leucine,isespeciallysignificantinproteinsynthesis.Leucineisanimportantactivatorintheprocessofproteinsynthesis.ItisatranslationinitiationfactorforMPS.

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Figure1:LeucineActivationPathway(8)8 AsshowninFigure1,leucineactivatesthemammaliantargetofrapamycin(mTOR),whichreducestheinhibitoryeffectof4E-BP1throughphosphorylation.Aproteinkinase,mTORalsophosphorylatesS6K1thatinturnphosphorylatesmanyproteinsleadingtotheinitiationandelongationstagesoftranslation.ThisisthetranslationresponsibleforMPS(8,9).8,9

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Table1:AminoAcidConcentrationsofVariousCommonDietaryProteinSources(10)10 Table1showsthatwheyproteinhasthehighestpercentageofleucine.Knowingthis,andleucine’scrucialroleinMPS,isanotherreasonwhywheyproteinishypothesizedtobethemosteffectiveinstimulatingmusclegrowth.ReviewofResearchStudiesTang,J.E.,Moore,D.R.,Kujbida,G.W.,Tarnopolsky,M.A.,&Phillips,S.M.(2009).Ingestionofwheyhydrolysate,casein,orsoyproteinisolate:effectsonmixedmuscleproteinsynthesisatrestandfollowingresistanceexerciseinyoungmen.JournalofAppliedPhysiology,107(3),987-992.doi:10.1152/japplphysiol.00076.2009 ThepurposeofthestudybyTangetal.wastomeasuretheshort-termresponseofskeletalmuscleproteinsynthesis(MPS)followingtheingestionofwhey,micellarcasein,andsoyproteins.Theseresponseswerelookedatbothatrestandfollowingresistanceexercise.ThisstudywaslookingspecificallyatthedifferenceofMPSbasedonthedifferentdigestionspeedsofeachprotein.Tangandhiscontributorshypothesizedthatbecausewheyproteinisthefastesttobeabsorbed,itwouldhavethegreatesteffectonMPS. Eighteenyoungmenwhoregularlyengagedinresistancetrainingweredividedintothreetreatmentgroupsthatwouldeachreceivedifferentkindsof

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proteins.Therewasnostatisticallysignificantdifferenceinage,weight,orheightbetweenthethreegroups.Afterabaselinebloodsamplewasdrawn,thesubjectscompletedintenseunilateralresistanceexercisesatequivalentrelativeworkloads.Oncetheexercisewascompleted,anotherbloodsamplewastaken,andthenthesubjectsconsumedtheirassigneddrink.Thedrinkswereaboutonehundredkilocaloriescontainingwhey(21.4g),casein(21.9g)orsoy(22.2g).Next,acontinuousinfusionofL-[ring-13C6]phenylalaninewasadministeredtomeasuremixedmusclefractionalsyntheticrate(FSR).Bloodsamplesweretakenat30,60,90,120,and180minutesafterconsumptionoftheproteindrink,fromwhichaminoacidandinsulinconcentrationsweretaken.Musclebiopsieswerealsotakenfromboththeexercisedandnon-exercisedlegs180minutesafterconsumption.

Figure2:FSRafteringestionofwheyhydrolysate,casein,orsoyproteinatrestandafterexercise(valuesaremeans+SD;n=6pergroup)(11).11*Significantlydifferentthancaseinforcorrespondingcondition(P<0.01)#Significantlydifferentfromsoyforcorrespondingcondition(P<0.05) Figure2showsthatatrest,wheyandsoygroupssawsignificantlygreaterFSRthancasein(P<0.01),andwhey.WheyFSRwashigherthansoyatrest,howeverthedifferencewasnotsignificant.Asexpected,FSRfollowingexercisewasgreaterthanatrestforallgroups.WheyFSRfollowingexercisewassignificantlygreaterthansoy(P<0.05)andcasein(P<0.01).InadditiontoFSR,bloodconcentrationsofessentialaminoacids(EAA)andleucineweresignificantlygreaterafterconsumptionofthewheyproteinthanthatofthesoyorcaseinproteins(P<0.05). Tang’sstudywasthefirsttogivedirectlymeasuredratesofmixedMPSinresponsetotheingestionofdifferentproteinsknowntohavedifferentratesofdigestion.Thisstudyshowedthatalthoughwheyandsoystimulatesignificantrises

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inbloodaminoacidconcentration,wheyisstillmoreeffectiveatproducingMPS.OnlyacuteMPSwaslookedatinthisstudy,uptoatimepointof180minutes;however,extensionofthetimeperiodswouldlikelynotproducedifferentMPSresultsbecauseaminoacidconcentrationwasbacktobaselinelevelsbyabout240minutespost-consumption.ThedifferencesinMPSfollowingthethreeproteinsbeinglookedatweresurprisingduetothesimilarproteindigestibility-correctedaminoacidscore(PDCAAS)ofwhey,soy,andcaseinproteins.Itwasthoughtthatbecausealloftheproteinsarecompletesourcesofallaminoacids,thattheyshouldbeabletosupportequalproteinsynthesis.Thisspeculationwasrationalizedbythedifferenceinleucinecontentandspeedofdigestion.ItwasspeculatedthatathresholdofleucinemightneedtobemetinthebloodtomaximizeMPS,andthatperhapssoy(andcasein)proteinalonedoesnotmeetthisthreshold. Thisstudythoroughlylookedatthemetabolicandphysiologicaleffectsofwhey,soy,andcaseinsupplementationallthewaydowntothecellularlevel.Itlookedatbloodsamplesandmusclebiopsiestogetawellroundedlookattheseeffects.Althoughtherewasnostatisticaldifferenceinheight,weight,oragebetweenthesubjectgroups,alimitationofthestudyisthattherewasnocontrolgroupreceivingnotreatment.Therewashowever,acomparisonbetweenrestandpost-exerciseMPSforeachtreatmentgroup.Theexerciseswerealsounilateral,soeachsubjecthadacontralaterallegforacontrolofsorts.Allsubjectswerealsoonacontrolleddietfortwodayspriortotrials.Areasonforthelackofatotalcontrolgroupmaybebecauseofoneothershortcomingofthestudy,alackofsubjects(18).Evenwiththeseshortcomings,thestudywasverycomprehensive,andeffectivelyevaluatedtheanaboliccapabilitiesofthesethreeproteins.Hartman,J.W.,Tang,J.E.,Wilkinson,S.B.,Tarnopolsky,M.A.,Lawrence,R.L.,Fullerton,A.V.,&Phillips,S.M.(2007).Consumptionoffat-freefluidmilkafterresistanceexercisepromotesgreaterleanmassaccretionthandoesconsumptionofsoyorcarbohydrateinyoung,novice,maleweightlifters.AmericanJournalofClinicalNutrition,86(2),373-381.Retrievedfrom<GotoISI>://WOS:000248629700015 Thesecondstudyinthisreview,byJosephHartmanandhiscollaborates,focusedonthelong-termconsequencesanddifferencesofmilk,soy,orcarbohydrateconsumptiononleanmassgainfromtraining.Thisstudyusedfifty-sixsubjectsinatwelveweek,fivedaysperweek,splitbodyresistanceexerciseprogram.Itwasathreegrouplongitudinaldesign.Thesubjectswererandomlyassignedtothemilk,soy,orcarbohydrategroup,whichisthedrinktheywouldconsumeimmediatelyfollowingexercise,andonehourafterexercise,forthedurationofthestudy.Allthreedrinkswereisoenergetic,andthemilkandsoydrinkswerealsoisonitrogenousandhadthesamemacronutrientratio.One-repetitionmaxtestingwasdonebeforetraining,everyfourweeksduring,andthreedaysafterthelasttrainingsessionforeachgrouptomonitorstrengthgains.Inordertodetermineadailymacronutrientintake,participantscompletedathreedayweighteddietrecordbeforeandduringthesixthandtwelfthweeks.Thisdatawas

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analyzedbyNUTRITIONISTVsoftware.Musclebiopsiesweretakenbeforeandafterthetwelve-weekprogramtolookatchangesinmusclefibertypes.Subjects’bodycompositionsweredeterminedviaawhole-bodydualenergyX-rayabsorptiometry(DXA)scanbeforeandafterthetwelveweeks.Atweeksevenoftheregimen,subjectshadblooddrawnbeforeexercise,immediatelyafterexercise,andat30,60,90,and120minutesfollowingexercise.Thiswastomeasureaminoacidconcentrationsandplasmainsulinlevels.Asmentionedabove,themainpurposeofthisstudywastolookatthedifferenceinleanmassaccretionbetweengroupsconsumingthedifferentdrinks.ThiswasdonebyusingtheDXAresultstocomparethechangesinfat-andbone-freemasses(FBFM)ofeachgroupoverthetwelve-weekperiod.

Figure3:IndividualandmeanchangesinFBFM.*Statisticallydifferentfromothergroups(P<0.01)(12)12 FigurethreeshowsthechangesinFBFM,withtheindividualpointsrepresentingeachsubject,andthehorizontallinesshowingthemeanchangesinFBFMforeachgroup.Thisfigureshowsthegreatestgaininleanmassfromthemilkgroup,followedbythesoyandcontrolgroups(P<0.01).Allofthesubjects’weightschangedsubstantiallyoverthetwelveweeks.Thecontrolgroupsawagainof2.3+1.1%oforiginalbodyweight;thesoygroupgained3.1+1.7%;andthemilkgroupexperiencedanaveragegainof3.9+1.2%ofbodyweight.Thisstudyalsolookedatstrengthgainsacrossthegroups,andalthoughtheywerenotsignificant,thereweredifferences.Themilkgroupoverallsawthegreateststrengthincreases,followedcloselybysoy,andthecontrolsawtheleastincrease. Thisstudylookedlessattheacuteeffectsandmoreatthechronicaffectsofdifferentproteinsupplementsonmusclegrowthandstrengthincreases.Thisstudy

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contrastedpreviousstudiesthatshowednosignificantdifferencebetweenmilkandcarbohydratesupplementationonmusclegrowth.Hartmanandhiscollaboratesbelievethepreviousstudiesmayhavebeentooshortindurationtoseealegitimatedifference.Thisstudyalsofoundmilksupplementationtoleadtogreaterfatlossalongwiththeincreasedleanmassgain.Hartmanandhiscolleaguesbelievethistobeduetogreatercalciumintake,andduetopropertiesofdairyproteinsthatacceleratelossofadiposetissueduringenergyrestriction. Prosofthisstudyincludearelativelylargenumberofsubjects,andacontrolgroup.Thetrainingprogramwasverycomprehensiveandpractical.Thisstudylookedatmultipleresponses,includingbodycomposition,strength,musclefiberchanges,andbloodresponses.Theinclusioncriteriaofthestudywereveryspecific,assubjectswerenotallowedtohaveliftedwithineightmonthsofparticipation,andcouldnothavebeenconsumingdietaryorproteinsupplementswithintheprevioussixmonths.Aconofthisstudywasthatthedietwasnotcontrolledforatanypoint,althoughdietaryanalyseswereperformed.Wilkinson,S.B.,Tarnopolsky,M.A.,MacDonald,M.J.,MacDonald,J.R.,Armstrong,D.,&Philips,S.M.(2007).Consumptionoffluidskimmilkpromotesgreatermuscleproteinaccretionafterresistanceexercisethandoesconsumptionofanisonitrogenousandisoenergeticsoy-proteinbeverage.AmericanJournalofClinicalNutrition,85(4),1031-1040.Retrievedfrom<GotoISI>://WOS:000245661700016 InthisstudybyWilkinsonetal.,theobjectivewastocomparedifferenceinproteinkinetics,muscleproteinbalance,andthefractionalsynthesisrateofmusclebetweensubjectssupplementedwitheitheramilkorsoyproteindrink.Thiswasarandomized,crossoverdesignstudyincludingeightmenwhoexercisedregularly.Eachsubjectperformedtwotrials,bothweretheexactsame,exceptinonetrialtheyconsumedthemilkproteindrink,anddrankthesoybeverageintheothertrial.Adifferentlegwasalsoexercisedineachtrial.Eachtrialconsistedofaunilaterallegexerciseboutatarelativeintensitytotheindividual’sone-repetitionmax.Thesubjectsconsumedeitherthemilkorsoyproteinbeverageafterexercise.Thedrinkorderandorderofthelegbeingtestedwasrandomized.Bloodsamplesweretakenimmediatelybeforeandafterexercise,andat30,60,90,120,and180minutespost-exercise.Musclebiopsieswereperformedimmediatelybeforeandafterexercise,andat60,120,and180minutesfollowingexercise. Themainresultofthisstudywastheeffectofeachdrinkonmuscleproteinaccretion,asmeasuredbyfractionalsyntheticrate(FSR).Figure4(below)showsthemeanFSRduringexerciseandthreehoursaftercompletionoftheworkoutandconsumptionofeitheramilkorsoybasedproteinbeverage.FSRwassignificantlyhigherinbothgroupsfollowingexerciseascomparedtoduringexercise(P<0.05).Furthermore,themilkgroupexperiencedasignificantlygreaterFSR(34%higher)threehoursafterexercisethandidthesoygroup(P<0.05).

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Figure4:Fractionalsyntheticrateofmuscleproteinsduringexerciseandthreehoursafterward.*Significantlydifferentfromthesoygroupatthegiventimepoint(P<0.05)†Significantly different from exercise (P<0.05)(2)2 Theonlyothersignificantdifferencefoundinthisstudywastotalaminoacidnitrogenbalance(NB).ThemilkgroupshowedahigherNBthanthesoygroupintheexercisedleg(P<0.05). Themainconclusionofthisstudywasthatproteinconsumptioncancreateananabolicenvironmentformuscleproteingrowth.TherewasasignificantlylargeruptakeofaminoacidsandgreaterrateofMPSfollowingmilkconsumptionratherthansoyconsumption.Thestudysuggeststhatthedifferenceinthedeliveryofaminoacidsleadstodifferentpatternsofaminoacidappearance,andthisleadstoadifferenceinMPSfollowingexercise. Thisstudyprovidedacomprehensivelookatnotonlymusclesynthesis,butataminoaciduptake,nitrogenbalance,andinsulinspikesresultingfromtheconsumptionofbothmilkandsoybasedproteinbeverages.Allofthesubjectswererelativelysimilarinage,weight,andheight.Thestudywascompletelyrandomized,andtheexercisewasunilateral,thuseachsupplementwasusedoneachsubject,ratherthanseparategroupsreceivingdifferenttreatments.Consofthisstudywouldbethenumberofsubjectswasverysmall,andtherewasnototalcontrolgroup,inwhichnosupplementwastaken. Conclusions Inconclusion,allthreestudiesinthisreviewsupportthehypothesisthatwheyproteinissuperiortobothsoyandcaseinproteinatincreasingmusclesize

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andstrength.Thesecondtwostudieslookedatmilkratherthanisolatedwhey,butitisknownthatwheyproteinisthemainproteininmilkcontributingtoMPS,ascaseinismuchlesssignificantinthisrole.ThestudybyTangetal.showedthatwheyproteinproducedgreaterFSRbothatrestandafterexercisethansoyandcasein.Thisstudyalsoshowedthatwheyproteinstimulatedagreaterriseinbloodessentialaminoacidconcentration,especiallyleucineconcentration,thantheothertwoproteins.Thesecondstudy,byHartmanetal.,demonstratedthatchronicmilkproteinsupplementationwithtrainingproducesagreatergaininleanmass,andlossoffatmass,thansupplementationwithsoyprotein.Inthethirdstudy,Wilkinsonetal.,FSRisshowntobe34%greaterfollowingmilkproteinsupplementationcomparedtosoyproteinsupplementation.FutureResearch Althoughallthreeofthesestudiesshowstrongevidencethatwheyproteinissuperiortosoyandcasein,thereisstillmuchworktobedone.Noneofthesestudiescontrolleddietthroughoutthetrials,whichcouldhaveabigimplicationofanabolicresponsessuchasmusclegrowth.Thesestudiesalsohadarelativelysmallnumberofsubjects(withtheexceptionofHartmanetal.).Itwouldbebeneficialtohavestudiesliketheseincludemoresubjects,soastostrengthenthedata.Itwouldalsobeinterestingtoseeiftheseproteinshaddifferenteffectsonmenversuswomen.Similarstudiescouldalsobeconductedcomparingdifferencesamongpeopleofdifferentracesorethnicities.Itwouldalsobebeneficialtoconductstudiesonproteinsupplementationinsports-specifictrainingregimensusedbyathletesintheirrespectivesports.Anothersteptoaddtostudieslikethesewouldbetolookatcreatinesupplementation,andhowitcouldbolsterorlessentheeffectsofdifferentproteinsupplements.Allofthesetopicsprovidepromisingareasofresearchforscientistsinthefield.

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consumptionofsoyorcarbohydrateinyoung,novice,maleweightlifters.AmericanJournalofClinicalNutrition.2007;86(2):373-381.