Harvard School ofPublicHealth
TheNutritionSource
FatsandCholesterol:Outwith theBad,Inwiththe
Good
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Table ofContents
•Introduction
• FrmnFoodtotheBloodstream
• DietandCholesterol:HowFatandCholesterolinFood
AffectBloodLevels
• DietaryFatsandHeat1Disease:Beyondthe"30Percent"Reconm1endation
• DietaryFatsandCancer
• DietaryFatandOtherChronicConditions
• DietatyFatandObesity
• TheBottom.Line:RecommendationsforFatIntake
• References
Introduction
.
"Eatalow-fat,low-cholesteroldiet"hasbeenthemantraforhealthfuleatingfordecades.Touted
asawaytoloseweightandpreventorcontrolheartdiseaseandotherchronicconditions,millionsofpeoplehavefollowed(or,morelikely,havetriedtofollow)thisadvice.Seeingatremendousmarketingopportunity,foodcompaniesre-engineeredthousandsoffoodstobelowerinfatorfatfree.Thelow-fatapproach toeatingmayhavemadeadifferencefortheoccasional individual,
butasanationithasn'thelpeduscontrolweightorbecomehealthier.Inthe1960s,fatsandoilssuppliedAmericanswithabout45percentoftheircalories;Q)about13percentofuswereobeseandunder1percent hadtype2diabetes,aseriousweight-relatedcondition.(2.3)Today,Americans takeinlessfat,gettingabout33percentofcaloriesfromfatsandoils;Q)yet34percentofuseobeseand8percenthavediabetes, mostwithtype2diabetes.)
Whyhasn'tcuttingfatfromthedietpaidoffasexpected?Detailedresearch-muchofitdoneatHarvard-showsthatthetotalamountoffatinthedietisn'treallylinkedwithweightordisease.(9.:9)Whatreallymattersisthetypeqffatinthediet.Badfats,meaningtransandsaturatedfats,increasetheriskforcertaindiseases.Goodfats,meaningmonounsaturatedandpolyunsaturatedfats,dojusttheopposite.Theyaregoodfortheheartandmostotherpartsofthebody.
Whataboutcholesterolinfood?Formostpeople,themixoffatsinthedietinfluencescholesterolinthebloodstream farmorethancholesterolinfooddoes.
From FoodtotheBloodstream
Almostallfoodscontainsomefat.Evenquintessentialfat-freefoodslikecarrotsandlettucecontainsmallamountsofthisnutrient.That'satestamenttohowimportantfatsareforlife.Fatprovidesaterrificsourceofenergyaswellasagreatdepotforstoringit.Itisanimportantpartofcellmembranes,helpinggovernwhatgetsintocellsandwhatcomesout.Thebodyusescholesterolasthestartingpointtomakeestrogen,testosterone,vitaminD,andothervitalcompounds. Fatsarealsobiologically activemolecules thatcaninfluencehowmusclesrespond
toinsulin's"openupforsugar"si!,TTial;differenttypesoffatscanalsofrreuporcooldowninflammation.
Fatandcholesterolcan'tdissolveinwaterorblood.Thebodygetsaroundthisbasicchemistryproblembypackagingfatandcholesterolintotiny,protein-coveredparticlescalledlipoproteins.Although lipoproteinscancarryquiteabitoffat,theymixeasilywithbloodandflowwithit.Someoftheseparticlesarebigandfluffy,otherssmallanddense.Themostimportant onesarelow-density lipoproteins,high-densitylipoproteins,andtriglycerides.
Q.\Vhat canIdotolowermy totalcholesterolandLDL?
A.SeveralstrategiescanhelpyoulowertheamountsoftotalandharmfulLDLcholesterolinyourbloodstream,andthusyourriskofheartdisease.(Readmore)
• Low-densitylipoproteins(LDL)canycholesterolfromthelivertotherestofthebody.Cellslatchontotheseparticlesandextractfatandcholesterolfromthem.WhenthereistoomuchLDLcholesterolintheblood,theseparticlescanformdepositsinthewallsofthecoronaryarteriesandotherarteriesthroughoutthebody.Suchdeposits,calledplaque,cannarrowarteriesandlimitbloodflow.Whenplaquebreaksapart,itcancauseaheartattackorstroke.Becauseofthis,LDLcholesterolisoftenreferredtoasbad,orharmful,cholesterol.
•High-densitylipoproteins(HDL)scavengecholesterolfromthebloodstream,fromLDL,and
fromarterywallsandfeny itbacktotheliverfordisposal.ThinkofHDLasthegarbagetrucksofthebloodstream. HDLcholesterolisoftenreferredtoasgood,orprotective,cholesterol.
• Triglyceridesmakeupmostofthefatthatyoueatandthattravelsthroughthebloodstream.
Asthebody'smainvehiclefortransportingfatstocells,triglyceridesareimportantforgoodhealth.Butasisthecaseforsomanythings,anexcessoftriglyceridescanbeunhealthy.
Ingeneral,theloweryourLDLandthehigheryourHDL,thebetteryourchancesofpreventingheartdiseaseandotherchronicconditions.GuidelinesfromtheNationalCholesterolEducationProgramsuggestspecifictargets.
DietandCholesterol:HowFatandCholesterolinFood
AffectBloodLevels
ThetypesoffatinthedietdeterminetoalargeextenttheamountoftotalandLDLcholesterolinthebloodstream.Cholesterolinfoodmatters,too,butnotnearlyasmuch.
WhatTypeofFat lsIt'?This tableshowsthepercentageofsaturated,monounsaturated,polyunsaturated,andtransfatincommonoilsandcookingfats.
TheBest DietistheOneYoutllFollow:ThePOUNDSLOST trialfound thatpeoplecanloseweight onanydiet- whetheritishighinfatorlowinfat- aslongastheystick toalower-calorieeating plan.
GoodFats:UnsaturatedFats
Unsaturated fatsarecalledgoodfatsbecausetheycanin1provebloodcholesterollevels,easeinflammation,stabilize heartrhythms,andplayanumberofotherbeneficial roles.Unsaturatedfatsarepredominantlyfoundinfoodsfromplants,suchasvegetableoils,nuts,andseeds.Theyareliquidsatroomtemperature.
Therearetwotypesofunsaturatedfats:
•Monounsaturatedfats arefoundinhighconcentrationsincanola,peanut,andoliveoils;avocados;nutssuchasahnonds,hazelnuts,andpecans;andseedssuchaspumpkinandsesameseeds. .
• Polyunsaturatedfatsarefoundinhighconcentrationsinsunflower,corn,soybean,andflaxseedoils,andalsoinfoodssuchaswalnuts,flaxseeds,andfish.OJnega-3fats,whicharefastbecoming thedarlingofthesupplementindustry,areanimportanttypeofpolyunsaturatedfat.Thebodycan'tmakethese,sotheymustcomefromfood. Anexcellent waytogetomega-
3fatsisbyeatingfishtwoorthreetimesaweek.Goodplantsourcesofomega-3fatsinclude
chiaseeds(soldasSalvia),flaxseeds,walnuts,andoilssuchasflaxseed,canola,andsoybean.
Dutchresearchersconductedananalysisof60trialsthatexaminedtheeffectsofcarbohydratesandvariousfatsonbloodlipidlevels.Intrialsinwhichpolyunsaturatedandmonounsaturatedfatswereeateninplaceofcarbohydrates,thesegoodfatsdecreasedlevelsofharmfulLDLandincreasedprotective HDL.(10)Morerecently,arandomizedtriallrnownastheOptimalMacronutrientIntakeTrialforHeartHealth(OmniHeart)showedthatreplacingacarbohydraterichdietwithonerichinunsaturatedfat,predominantlymonounsaturatedfats,lowersbloodpressure,improves lipidlevels,andreducestheestimatedcardiovascularrisk.(!1)
Mostoeooledon't1!etenoughofthesehealthfulunsaturatedfatseachday.No
Foryears,margarinewaspromotedasaheart-healthyalternativetobutter.Sincemargarinewasmadefromunsaturatedvegetableoils,mostpeopleassumeditwouldbebetterforlong-termhealththanbutter,whichwasknowntocontainalot ofcholesterolandsaturatedfat.That
assumptionturnedouttobewrong.Researchshowedthatsomeformsofmargarinespecificallythehardstickmargarines-wereworsefortheheartthanbutter.Thiswasbecausetheycontainedlargeamountsoftransfatsfrompartiallyhydrogenatedoils.
1ublishedregardingtheirintake.Prudenttargetsiesfrommonounsaturatedfatsand8to10yunsaturatedfats.Sincenooneeatsbypercentageofthumb istochooseunsaturatedfatsover
:d,sowedon't needtoeatanyofit.That's whyewedon'tneedtoeatanyofit,andithas
theUnited States andotherdevelopedcountries,poultrywithskin,andwhole-milkdairyproducts
: arealsohighinsaturatedfats,includingcoconut
TI1.eNurses'HealthStudyfoundthat women aturatedfatsboosttotalcholesterolbyelevatingwhoate4teaspoonsofstickmargarineaday .Isoraises theprotectiveHDL.Unsaturatedfatishada50percentgreaterriskof heartdisease rolandraises thegood.
thanwomenwhoaten1.argarineonlyrarely.
(21.) 1takeofsaturatedfatsaslowaspossible.
vegetableoilsthataremainlyunsaturatedfats,so
Soshouldyouchoosebutterovermargarine?Wheneverpossible,skipbothandusealiquidvegetableoiL At thetable,trydippingbreadinoliveoil insteadofslatheringitwithbutterormargarine.When
sauteing,tryusingolive,canola,oranother
!rcentoftotalcaloriesorlowerisagoodtarget.saturatedfatinourdiets,sokeepingtheselowis
liquidvegetableoil,withalittlebitofbutterLonlycalled transfats,aremadebyheating liquid
forflavor.Ifyouneedsomethingspreadable,ofhydrogengas,aprocesscalled hydrogenation.
chooseasoftmargarinethatisnotonlytransableoilsmakes themmorestable andlesslikely
freebutlowinsaturatedfat.Anumberofsoftmargarinesaremadefromablendofhealthfuloils,andsomehavetheaddedbenefitofcontainingcholesterol-loweringplantsterols.Keepinmindthatyouneedtoeattwoservingsofthesesterol-containingmargarinesadaytoput asmalldentinyourLDLleveL
Readmoreabouthowtospot transfatonfoodlabels.
ilintoasolid,whichmakes transportationeasier.
:peatedheatingwithoutbreakingdown, makingLatingavegetableoilcreates afatthatactslikeagenatedoilshavebeenamainstayinrestaurants
MostofthetransfatsintheAmericandietcomefromcommerciallyprepared bakedgoods,margarines,snackfoods,andprocessed foods,alongwithFrenchfriesandotherfriedfoodspreparedinrestaurantsandfastfoodfranchises.
Transfatsareworseforcholesterollevelsthansaturated fatsbecausetheyraisebadLDLandlowergoodHDL.Theyalsofireinflammation,01.) anoveractivityoftheimmunesystemthathasbeenimplicatedinheartdisease,stroke,diabetes, andotherchronicconditions.Evensmallamountsoftransfatinthedietcanhaveharmfulhealtheffects.Foreveryextra2percentofcaloriesfromtransfatdaily- abouttheamountinamediumorderoffast-foodFrenchfries- theriskofcoronary heartdiseaseincreasesby23percent.Eliminating transfatsfromtheU.S.foodsupplycouldpreventbetween6and19percentofheartattacksandrelateddeaths,ormorethan
200,000eachyear.(13)
TheaverageAmerican eatsaboutsixgramsoftransfatsaday.Ideallythatshouldbeundertwogramsaday,orzeroifpossible.Anewlabelinglawthatforcesfoodcompaniestolisttransfats
onthelabelshouldhelpcurbtheconsumptionoftheseharmfulfats.Notonlycanconsumers nowseewhichproductscontaintransfats- something thatwasn'teasilydoneinthepast-butmanyfoodmakersarenowtryingtoclaimthehighground byusingtrans-freeoilsandfatsintheirproducts.
Astransfatintakedwindlesindevelopedcountries, itisontheriseindevelopingnations.Inexpensivepartially hydrogenatedsoybeanoilhasbecomeastaplenotonlyforthefoodindustrybutforhomeuse.Thisshiftawayfromtraditionalcookingoilsandtowardtrans-richpartiallyhydrogenatedoilsiscontributingtotheslowlygrowing epidemicofcardiovasculardiseaseindeveloping nationsaroundtheworld
CholesterolinFood
Thediscovery halfacentury agothathighbloodcholesterollevelswerestronglyassociated withanincreasedriskforheartdiseasetriggerednumerouswarningstoavoidfoodsthatcontaincholesterol,especiallyeggs,liver,shrimp,andlobster.Thatadvicewassomething ofaredherring;for
exampleeatingshrimpandlobsterdoesn'traiseLDLcholesterol. Also,mostpeoplemakemorecholesterolthantheyabsorbfromtheirfood.Abodyofscientific studiesshowsonlyaweakrelationshipbetweentheamountofcholesterolapersonconsumes andhisorherbloodcholesterollevels(.1.1)(weakbutimportant forheartdisease).Instudiesofmorethan80,000femalenurses,Harvardresearchersfoundthatconsumingaboutaneggadaywasnotassociated
withhigher riskofheartdisease(toofewwomen inthestudywereeating morethananeggadaytoevaluatetheeffectsofhighereggintakes).(15,16)Onenoteofcaution:Amongwomeninthisstudy withdiabetesandinanotherstudy ofmenwithdiabetes,higher eggconsumptionhasbeenassociatedwithincreasedrisksofheart disease.
Researchsuggeststhatmoderateeggconsumptioncanbepartofahealthydiet.Butthisresearchdoesn't givethegreen lighttodailythree-eggomelets,especiallyforpeople whoalready have heartdiseaseordiabetes.Readmoreabouteisand hearthealth.
Formostpeople, theamountofcholesteroleaten hasonlyamodestimpact ontheamountofcholesterolcirculatingintheblood. (17)Forsome people,though,blood cholesterollevelsriseandfallverystrongly inrelationtotheamountofcholesteroleaten. Forthese"responders,"avoidingcholesterol-richfoodscanhaveasubstantialeffect onbloodcholesterollevels.Unfortunately,atthispoint thereisnowayotherthanbytrialanderrortoidentifYrespondersfrom non-responderstodietarycholesterol.
DietaryFatsandHeartDisease:Beyondthe"30Percent"Recommendation
Foryears, theparty linefromtheAmericanHeart Ass?ciation,NationalInstitutesofHealth, WorldHealth Organization,andotherswastoreducedietaryfat.They generallycalled forlimitingfatintaketounder 30percentofdailycalories.Oneproblemwithagenericlower fatdietisthatitpromptsmostpeopletostopeating fatsthataregoodfortheheartalong withthosethat
arebadforit.Inplaceoffats,many peopletumtofoodsfullofeasilydigestedcarbohydrates,ortofat-freeproductsthatreplacehealthfulfatswithsugarandrefmedcarbohydrates.
Therewasn't muchevidencetosupportthenotion oflow-fatdietsinthebeginning.(1.8_)There iseven lessnow.Numerousreports overtheyearshavequestionedthewisdomofrecommendinglow.:.fatdietsforpreventingorretardingheartdisease.Abignailinthecoffm came fromtheWomen'sHealth InitiativeDietaryModificationTrial,publishedintheFebruary8,2006,Journal
oftheAmericanMedicalAssociation.(_B.)This eight-yeartrial,whichincludedalmost 49,000women,foundvirtuallyidenticalrates ofheart attack,stroke,andother forms ofcardiovascular
diseaseinwomenwhofollowedalow-fatdietandinthosewomenwhodidn't.What'smore,
-
womenonthelow-fatdietdidn't lose-orgain-anymore weightthan womenwhofollowed
theirusual diets.(1)
This randomizedtrialsupportsprior rmdingsfromtheNurses'HealthStudy (l9)andtheHealthProfessionalsFollow-upStudy. (19)Inbothofthese, nolink wasseen betweentheoverallpercentageofcaloriesfromfatandanyimportanthealth outcome,includingcancer,heart disease,andweightgain.
What wasimportantinthesestudieswasthetypeoffatinthediet.(20)Ounceforounce, transfatsarefarworsethansaturatedfatswhen itcomestoheartdisease.IntheNurses' HealthStudy,replacingjust30caloriesofcarbohydrates(7grams)every daywith30caloriesoftransfats(4grams)nearlydoubledtheriskforheart disease.(£1)Saturatedfatsincreasedtheriskaswell, butnotnearlyasmuch.
Forgood fats,there isconsistentevidencethathigherintakeofeithermonounsaturatedorpolyunsaturatedfat(especiallythelatter) lowerstheriskforheart disease.IntheNurses'HealthStudy,replacing80caloriesofcarbohydrateswith80caloriesofeitherpolyunsaturatedormonounsaturatedfatsloweredtheriskforheart diseasebyabout 30to40percent.(20)
Dietary FatsandCancer
Heart diseaseisnottheonly conditionthathasbeenlinkedwithfatintake.Researchersoncesuspectedanassociationbetweendietaryfatandcertaincancers.Hereagain,inadults,thepercentageofcaloriesfrom totalfatconsumedappearstohavenoimportantrelationtorisk,andnoclearevidencehaslinkedanyspecifictypeoffatwith cancerincidence.
BreastCancer
Bytheearly 1980s,most nutritionexpertsbelievedthatdietaryfatwasamajorcauseofbreastcancer.(22,23)This thinkingwaslargelybased oninternationalcomparisonsshowinghigherbreast cancerratesincountrieswithhigherpercapita fatintake.Butsuch comparisonsareverybroad innature.Asmore detailedstudieswere performedoverthenextcoupleofdecades,theapparentlink betweentotalfatintakeandbreast cancerhasfaded.(24) TheWomen'sHealthInitiativeDietaryModificationTrial,whichwasspecificallydesignedtoexaminetheeffect ofalow-fatdietonthedevelopmentofbreast cancer,showedsimilarrates ofbreastcancerinwomen
eatingalow-fatdietandinthoseeatinga"regular" diet.CDOnerecentstudyfromtheNationalInstitutesofHealth-AARPDietandHealthStudy,(25)foundaveryweakpositiveassociationbetweenfatandpostmenopausalbreastcancer,butwhencombined withthemanyotherstudiesdetailedabove,theoverallevidencedoesnotsupport arelationship between totalfatintakeandbreastcancer.
Although studies-includingthosebyHarvardresearchers-ofdifferenttypesoffathavelargelyfailedtofmdalinkwithbreastcancer,someevidencesuggeststhatanimalfatintakemaybelinkedtohigherriskofbreastcancer.IntheNurse'sHealthStudyII,premenopausalwomenwhoatedietshighinanimalfathada40to50percent higherriskofbreastcancer,compared towomenwhoatetheleastanimalfat.(26)Becausevegetablefatwasnotrelatedtoriskofbreast
cancer,thesefindingssuggestthatredmeatandhigh-fatdairyproductsmaycontainotherfactors,suchashormones,thatincreaseriskofbreastcancer.SomeEuropeanstudieshavereportedsuggestive fmdingsoflowerbreastcancerriskamongwomenwithahighintakeofmonounsaturatedfats(mainly intheformofoliveoil).(27,28)
ColonCancer
Aswithbreastcancer,internationalcomparisonsinitiallysuggestedanassociationbetweentotaldietaryfatintakeandcoloncancerrisk.Butlaterstudiescontradictedtheseearlierfmdingsandrevealedinsteadanassociationthatwasweakatbest.Aswasthecasewithbreastcancer,womenintheWomen's HealthInitiative DietaryModificationTrialwhoatealow-fatdietdevelopedcoloncanceratthesamerateaswomenwhodidn't.(Q)Althoughfatintakedoesn'tseemtoincreasecoloncancerrisk,thereisconvincingevidencethathighconsumptionofredmeat(beef,pork,andlamb)andprocessed meat(hotdogs,bacon,anddelimeats)doesincreasecoloncancerrisk.(29)It'sbesttolimitredmeatconsumptiontonomorethan18ouncesperweek,andtoavoidprocessed meats.
ProstateCancer
Although theexactconnectionbetweendietaryfatandprostatecancerisfarfromclear,thereissomeevidencethatdietshighinanimalfatandsaturatedfatincreaseprostatecancerrisk.However,somestudieshavealsoshownnoassociation,whileothershaveimplicatedunsaturatedfats.Clearlymuchmoreresearchisneededtoclearuptheexactlinksbetweendietaryfatandprostatecancer.
OtherCancers
Preliminaryresearchhasalsolinkedtheintakeofcertainkindsfatwithothercancers,thoughmuchmoreresearchisneededtoconfirmtheseresults.IntheNurses'HealthStudy,Harvardresearchersfoundthatahighintakeoftransfatswasassociatedwithriskfornon-Hodgkin'slymphoma.
DietaryFatand OtherChronicConditions
Althoughcardiovascular diseaseandcancerhavereceivedthelion'sshareofresearchers'attention,thereisasmallbutgrowingbodyofworkontheeffectsofdietaryfatsonconditionssuchasosteoporosis,(30)age-relatedmemoryloss,(11)maculardegeneration,(32)multiple
sclerosis,G?J)infertility,(34)andotherchronicconditions.Thesefmdings,whicharestillearly,
donotprovideanyevidencetomodifyrecommendations basedonthepreventionofcardiovascular disease.
DietaryFatand Obesity
Itisacommonbeliefthatthemorefatyoueat,themoreweightandbodyfatyougain.Thisbeliefhasbeenbolsteredbymuchofthenutritionadvicegiventopeopleoverthepastfewdecades,whichhasfocusedonloweringtotalfatintakewhileincreasingcarbohydrateintake.Butthe
notionthatfoodfatequalsbodyfatisn'tcompletelytrue,andtheadvicehasbeenmisguided.Forexample,whileAmericanshavegraduallydecreasedtheproportionofcaloriestheygetfromfatoverthepastfewdecades,ratesofobesityhaveincreasedsteeply.(l)
Overtheshortterm,followingalow-fatdietdoesleadtoweightloss.Butsodoesfollowingahigh-fat,low-carbohydrate diet.Orahigh-protein,low-carbohydrate diet.Actually,almostanydietthathelpsyoutakeinfewercaloriesworksovertheshortterm.Inotherwords,formostpeoplelow-fatdietsoffernoapparentadvantagesoverdietswithfatlevelsclosetothenationalaverage.ThiswasdemonstratedintheWomen'sHealthInitiativeDietaryModificationTrial.Womeninthistrialwhowereassignedtoalow-fatdietdidnotlose,orgain,moreweightthanwomeneatinga"usual"diet.(1)Morerecently,POUNDSLOST(PreventingOverweightUsingNovelDietaryStrategies),atwo-yearhead-to-headtrialcomparingdifferentweightlossstrategiesfoundthatlower-fatdiets(20percentofcaloriesfromfat)werenomoreeffectivethanhigher-fatdiets(40percentofcaloriesfromfat)inthelongrun.(35)(ReadmoreaboutthePOUNDSLOSTdietstudy.)
Althoughmoreresearch isneeded,aprudent recommendationforlosingweightormaintainingahealthyweightistobemindful oftheamountoffoodyoueatinrelation totheamountofcaloriesyouburninaday.Amoderateintakeoffats,withanemphasisonhealthful unsaturatedfats,fits
infinewithaweight-lossorweight-maintainingdiet.
TheBottomLine: RecommendationsforFatIntake
Avocadoisagreatsourceofhealthyunsaturatedfats.Trythisrecipefor
ruacamolefromTheCulinaryInstituteof
America.
Althoughthedifferenttypesoffathaveavaried-andadmittedlyconfusing-effectonhealthanddisease,thebasicmessageissimple:Outwiththebad,inwiththegood.Asyoulimittheamountoftransandsaturatedfatsinyourdiet,astheAmericanHeartAssociation,NationalCholesterolEducationProgram,andothersrecommend,keepinmindth«tthereisnogoodevidence thatreplacingsaturatedfatwithcarbohydrateswillprotectyouagainstheartdisease,whilethereissolidproofthatreplacingsaturatedfatwithunsaturatedfatswillhelp.
• Trytoeliminatetransfatsfrompartiallyhydrogenatedoils.Checkfoodlabelsfortransfats;
avoidfriedfastfoods.
• Limityourintakeofsaturated fatsbycuttingbackonredmeatandfull-fat dairy foods.Tryreplacingredmeatwithbeans,nuts,poultry,andfishwheneverpossible,andswitchingfromwholemilkandotherfull-fatdairyfoodstolowerfatversions.
• Inplaceofbutter,useliquidvegetableoilsrichinpolyunsaturatedandmonounsaturatedfatsincookingdatthetable.
•Eatoneormoregoodsources ofomega-3 fatseveryday-fish,walnuts, canolaorsoybeanoil,
ground flaxseedsorflaxseed oil.