The Safe and Effective Use of Plant-Based Diets with Guidelines for Health Professionals

Abstract

Plant-based diets, defined here as including both vegan and lacto-ovo-vegetarian diets, are growing in popularity throughout the Western world for various reasons, including concerns for human health and the health of the planet. Plant-based diets are more environmentally sustainable than meat-based diets and have a reduced environmental impact, including producing lower levels of greenhouse gas emissions. Dietary guidelines are normally formulated to enhance the health of society, reduce the risk of chronic diseases, and prevent nutritional deficiencies. We reviewed the scientific data on plant-based diets to summarize their preventative and therapeutic role in cardiovascular disease, cancer, diabetes, obesity, and osteoporosis. Consuming plant-based diets is safe and effective for all stages of the life cycle, from pregnancy and lactation, to childhood, to old age. Plant-based diets, which are high in fiber and polyphenolics, are also associated with a diverse gut microbiota, producing metabolites that have anti-inflammatory functions that may help manage disease processes. Concerns about the adequate intake of a number of nutrients, including vitamin B12, calcium, vitamin D, iron, zinc, and omega-3 fats, are discussed. The use of fortified foods and/or supplements as well as appropriate food choices are outlined for each nutrient. Finally, guidelines are suggested for health professionals working with clients consuming plant-based diets.

Full text

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Nutrients2021,13,4144.https://doi.org/10.3390/nu13114144www.mdpi.com/journal/nutrients
Review
TheSafeandEffectiveUseofPlant‐BasedDietswith
GuidelinesforHealthProfessionals
WinstonJ.Craig
1,
*,AnnReedMangels
2
,UjuéFresán
3
,KateMarsh
4
,FaythL.Miles
1,5
,AngelaV.Saunders
6
,
EllaH.Haddad
1
,CelineE.Heskey
1
,PatriciaJohnston
1
,EnetteLarson‐Meyer
7
andMichaelOrlich
5

1
CenterforNutrition,HealthyLifestyles,andDiseasePrevention,SchoolofPublicHealth,LomaLinda
University,LomaLinda,CA92354,USA;fmiles@llu.edu(F.L.M.);ehaddad@llu.edu(E.H.H.);
cheskey@llu.edu(C.E.H.);pjohnston@llu.edu(P.J.)
2
VegetarianResourceGroup,Baltimore,MD21203,USA;reedmangela@gmail.com
3
eHealthGroup,InstitutodeSaludGlobalBarcelona(ISGlobal),08036Barcelona,Spain;
ujue.fresan@isglobal.org
4
PrivatePractice,Chatswood,NSW2067,Australia;drkatemarsh@gmail.com
5
SchoolofMedicine,LomaLindaUniversity,LomaLinda,CA92354,USA;morlich@llu.edu
6
NutritionInsights,SanitariumHealthFoodCompany,BerkeleyVale,NSW2261,Australia;
angela.saunders@sanitarium.com.au
7
HumanNutrition,Foods,andExerciseVirginiaTech,Blacksburg,VA24061,USA;enette@vt.edu
*Correspondence:wcraig@llu.edu
Abstract:Plant‐baseddiets,definedhereasincludingbothveganandlacto‐ovo‐vegetariandiets,
aregrowinginpopularitythroughouttheWesternworldforvariousreasons,includingconcerns
forhumanhealthandthehealthoftheplanet.Plant‐baseddietsaremoreenvironmentally
sustainablethanmeat‐baseddietsandhaveareducedenvironmentalimpact,includingproducing
lowerlevelsofgreenhousegasemissions.Dietaryguidelinesarenormallyformulatedtoenhance
thehealthofsociety,reducetheriskofchronicdiseases,andpreventnutritionaldeficiencies.We
reviewedthescientificdataonplant‐baseddietstosummarizetheirpreventativeandtherapeutic
roleincardiovasculardisease,cancer,diabetes,obesity,andosteoporosis.Consumingplant‐based
dietsissafeandeffectiveforallstagesofthelifecycle,frompregnancyandlactation,tochildhood,
tooldage.Plant‐baseddiets,whicharehighinfiberandpolyphenolics,arealsoassociatedwitha
diversegutmicrobiota,producingmetabolitesthathaveanti‐inflammatoryfunctionsthatmayhelp
managediseaseprocesses.Concernsabouttheadequateintakeofanumberofnutrients,including
vitaminB12,calcium,vitaminD,iron,zinc,andomega‐3fats,arediscussed.Theuseoffortified
foodsand/orsupplementsaswellasappropriatefoodchoicesareoutlinedforeachnutrient.Finally,
guidelinesaresuggestedforhealthprofessionalsworkingwithclientsconsumingplant‐baseddiets.
Keywords:plant‐baseddiets;vegetarian;vegan;sustainability;microbiome;vitaminB12;CV
disease;diabetes;bonehealth;lifecycle

1.Introduction
Interestinplant‐baseddietshassoaredinthepastdecadeforamyriadofreasons[1].
Peopleareconcernedaboutissuessuchastheirhealth,climatechange,thesustainability
ofthefoodproductionsystem,andthewelfareofanimals.Aplant‐baseddietisdefined
invariousways.Forsomeitmeanseatingfoodsmostly,butnotentirely,ofplantorigin,
whileforothersitmeanseatingonlyplant‐basedfoods.Inthismanuscript,wechoseto
restrictthetermplant‐basedtoincludebothvegandiets(totalplant‐basednutrition)and
lacto‐ovo‐vegetariandiets(thisallowsfortheconsumptionofdairyproductsandeggs).
Wedonotincludeadiscussionofflexitarian,semi‐vegetarian,orpesco‐vegetarianeating
patterns,astheydonotfitintoourdefinitionofplant‐baseddiets.
Citation:Craig,W.J.;Mangels,A.R.;
Fresán,U.;Marsh,K.;Miles,F.L.;
Saunders,A.;Haddad,E.;Heskey,C.;
J
ohnston,P.;Larso
n
‐Meyer,E.;etal.
TheSafeandEffectiveUseofPlant‐
BasedDietswithGuidelinesforHealth
Professionals.Nutrients2021,13,4144.
https://doi.org/10.3390/nu13114144
AcademicEditor:StephenIves
Received:27October2021
Accepted:17November2021
Published:19November2021
Publisher’sNote:MDPIstays
neutralwithregardtojurisdictional
claimsinpublishedmapsand
institutionalaffiliations.

Copyright:©2021bytheauthors.
LicenseeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsand
conditionsoftheCreativeCommons
Attribution(CCBY)license
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s/by/4.0/).

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Thispaperwilldiscusstheenvironmentalissuesandthebenefitsfortheplanetof
significantlyreducingoreliminatingmeatanddairyfoodsfromourdiet.Inaddition,it
outlinesthetherapeuticadvantagesofaplant‐baseddietformanagingthechronic
diseasesofWesternsociety,suchasobesity,cardiovasculardisease(CVD),cancer,and
diabetes.Aplant‐baseddietisalsoshowntohaveasubstantialimpactuponthe
compositionandfunctionofthegutmicrobiome,whichinturninfluencesouroverall
health.Furthermore,thesafetyoffollowingaplant‐baseddietduringallstagesofthelife‐
cycleisaddressed.Finally,questionswereraisedabouttheadequacyofaplant‐baseddiet
withrespecttoeightkeynutrients.Thesearediscussedindetail,withsolutionssuggested
astohowonecanmeetthedietaryrequirementsthroughfoodchoicesand/or
supplementation.Somesimpleguidelinesaregivenforhealthprofessionalstoeffectively
servethegrowingpopulationofthoseconsumingaplant‐baseddiet.
2.CurrentTrends
Internationally,theprevalenceoffollowingavegetariandietvariesbycountry,but
itisgenerallyestimatedtobelessthan10%ofthepopulation.TheexceptionisIndia,
where20%ormoreofadultsarevegetarian[2,3].IntheUnitedStates,anationwidepoll
in2020foundthatapproximately6%ofadultsfollowedavegetariandiet,withhalfof
thembeingvegans[4].AsimilarU.S.pollfoundthatapproximately2%of8‐to17‐year‐
oldchildrenfollowedavegandiet,and3%followedanon‐veganvegetariandiet[5].
Globally,themarketforalternativestodairyproductsisexpectedtoreach$US25
billionby2026[6].U.S.retailsalesofplant‐basedfoods(plant‐baseddairyalternatives
andplant‐basedmeats)increased27%between2019and2020,withatotalplant‐based
marketvalueestimatedat$7billion[7],suggestingagrowingconsumerinterestinnon‐
animalproducts.
The2020–2025DietaryGuidelinesforAmericansendorsesa“HealthyVegetarian
DietaryPattern”asoneofthreedietarypatternsthatcan“betailoredtomeetculturaland
personalpreferences”[8].Thereareversionsofthisplanforagesoneyearandolder.The
GuidelinesalsoencourageallAmericanstoeatmoreplantfoods,includingdriedbeans,
wholegrains,fruits,vegetables,andnuts.Manyothercountriespromoteplant‐based
dietsintheirdietaryguidelines[9].
Withagrowinginterestinvegetarianeating,establishmentssuchascollegesand
universities,schoolfoodservices,airlines,restaurants,prisons,employeefoodservices,
nursinghomes,andhospitalsareincreasinglyprovidingvegetarianoptions[10–12].
3.EnvironmentalSustainabilityofVegetarianDiets
Theproductionofdifferentfoodscanhaveverydiverseenvironmentalimpacts.
Thereisalargevariationintheecologicalfootprintofanimal‐basedproducts,with
ruminantmeatbeingespeciallydetrimentalfortheenvironmentascomparedwithother
productssuchaspork,whitemeat,oreggs[13–15].Anincreasingbodyofdataprovides
evidencethatenvironmentaldegradation,throughtheemissionsofgreenhousegas
(GHG)andotherpollutants,andtheuseofearth’sresources,suchaswaterandland,in
theproductionofplant‐basedfoodsaresignificantlylowerthanthatfromanimal‐based
foods[13–15].Certainly,theeffectsofthelowest‐impactanimalproductsaretypically
greaterthanthoseofplant‐basedalternatives,eveninthecaseofhighlyprocessedplant‐
basedmeatanalogs[14,16].Theproductionofplant‐basedproductsismoreefficient
regardlessofwhetherthecomparisonismadebyweightofproduct,perserving,per
calories,orevenproteincontent[14,15,17,18].Producingthesameamountofproteinfrom
tofu(soybeans)incomparisontobeefproteinrequires74timeslesslandandeighttimes
lesswater,whiletheGHGemissionsare25timeslowerandtheeutrophication(aprocess
drivenbytheenrichmentofwaterbynutrients,especiallycompoundsofnitrogenand/or
phosphorus,leadingtoanincreasedgrowth,primaryproductionandbiomassofalgae;
changesinthebalanceoforganisms;andwaterqualitydegradation[19])potentialis
reducedby39times[14,18].Evenifcomparedtoeggprotein,tofuproteinrequiresalmost

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threetimeslesslandandsixtimeslesswater,whiletheGHGemissionsareonlyhalfof
thatfromeggprotein,andtheeutrophicationpotentialisfivetimeslower[14,18].
Likewise,areductionofanimal‐basedfoodsinthedietgoeshandinhandwitha
decreaseinthedietaryenvironmentalimpact[20,21].Vegetariandiets,bothlacto‐ovo‐
vegetarianandvegan,havebeendescribedasmoreenvironmentallysustainablethan
thosedietsincludingmeat.Areviewstudyconcludedthattheadoptionoflacto‐ovo‐
vegetariandietscouldreducethedietaryGHGemissionsby35%,landuseby42%,and
freshwateruseby28%[20].Adoptingavegandietwouldleadtoaroundone‐halfofboth
GHGemissionsandlanduseofthatofcurrentdietarypatterns.Oneshouldnotethat
thereissubstantialvariabilityinthedietaryenvironmentalimpactofthoseconsuming
vegetariandiets.Inthefinalanalysis,anyenvironmentalbenefitswoulddependonthe
quantityandthespecificfoodsconsumed.Overconsumptionofcalories,ahighintakeof
fruitstransportedbyplane,ortheconsumptionoflargequantitiesoffattydairyproducts,
suchascheeseorbutter,inlacto‐ovo‐vegetariandietscouldjeopardizeanypotential
benefitfromtheavoidanceofmeat.
Studiessuggestthattheadoptionofnutritionallybalancedvegetariandiets,bothin
developedanddevelopingcountries,couldbeaneffectivestrategyforreducingGHG
emissionsworldwide[22,23].Thisdietarytransitionwouldbemoderatelyeffectivein
reducingfertilizerapplicationandwoulddecrease,althoughtoalesserextent,cropland
andfreshwateruse[23].Altogether,embracingabalancedvegetariandiet,especiallyin
developedcountries,couldbeaneffectivestrategyforreducingthefoodsystem’s
environmentaldegradationandreducingouruseoftheearth’sresources.
4.Plant‐BasedDietsandChronicDiseases
4.1.CVD,IncludingHyperlipidemia,IschemicHeartDisease,Hypertension,andStroke
CVDcontinuesasthemostcommoncauseofdeathanddisabilityintheU.S.and
globally[24,25].TheleadingriskfactorsforCVDincludedyslipidemia,excessweight,
hypertension,glucometabolicdisorders,anddiabetesandareattributedtopoordiets
[26,27].Comparedtoomnivorousdiets,vegetarianandplant‐baseddietsrichinwhole
grains,legumes,vegetables,fruits,nuts,andseedshavebeenassociatedwithsubstantial
reductionsinseveralmodifiableriskfactors,includingbodymassindex(BMI)andwaist
circumference[28,29],atherogeniclipoproteinconcentrations[29,30],bloodglucose[28],
inflammation[31],andbloodpressure[32].
Theresultsofrandomizedcontrolledtrials(RCT)ofveganandvegetarian
interventionsalongwithsystematicreviewsandmeta‐analysesofsuchstudiesshow
improvementsinseveralintermediatecardiometabolicriskmarkers,includingbody
weightandbloodlipids[33–37],andcardiometabolicriskprofiles[38].Datafrom
relativelylong‐term(years)clinicalinterventionstudieswithintensivelow‐fatvegetarian
[39]andvegandiets[40]showreversalsincoronaryarterydiseaseinindividualswith
CVD.Duetolowersaturatedfatandcholesterollevelsandmoreoptimalplantsteroland
fibercontent,greaterfavorableeffectsofvegandietsonheartdiseaseriskfactorsare
expected.Avegandiet,comparedtotheAmericanHeartAssociation(Dallas,TX,USA)
dietforcoronaryheartdisease(CHD),resultedinsimilarreductionsinBMI,waist
circumference,markersofglycemiccontrol,bloodlipids,anda32%lowerhigh‐sensitivity
C‐reactiveprotein(apro‐inflammatorymarker)[31].
IntheAdventistHealthStudy‐2(AHS‐2),vegetarianshada13%and19%lowerrisk
ofCVDandischemicheartdisease(IHD)mortality,respectively,comparedwithnon‐
vegetarians.Thisdifferenceoccurredinspiteofthefactthatthenon‐vegetariansinthe
cohortconsumedlessmeatthanthegeneralpopulation.Bloodpressurelevelsinvegans
andvegetarianswerealsolowerthanthoseoftheomnivores.Metabolicsyndromeand
type2diabetes(T2D)areprimeriskconditionsforCVDandstroke.Areducedprevalence
oftheseconditionswasobservedinveganandvegetarianparticipantsofAHS‐2[28,41].

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TheEPIC‐Oxfordstudyofvegetarians,vegans,andhealth‐consciousindividuals
reportedthattheriskofincidentIHDhospitalizationsanddeathscausedbycirculatory
diseasewas32%lowerinvegetariansthaninnon‐vegetarians[42].The18‐yearfollow‐up
showedlowerratesofIHDinvegetariansbuthigherratesofhemorrhagicandtotalstroke
[43].Redmeatintake,bothprocessedandunprocessed,wasassociatedwithCHDriskin
malehealthprofessionals[44].Inthelargeprospectivecohortofmenandwomenofthe
USNationalInstitutesofHealth—AARPDietandHealthStudy,higherplantprotein
intakewasassociatedwithreducedCVDmortality[45].IntheAtherosclerosisRiskin
Communitiesstudy,higherintakesofplant‐baseddietsscoredashealthywereassociated
withalowerriskofincidentCVDandCVDmortality[46].
PooleddatafromsevenprospectivecohortstudiesshowedareducedCHDincidence
andmortalityof28%and22%,respectively,associatedwithvegetariandiets.No
associationwithCVDorstrokemortalitywasseen[47].Similarly,acomprehensive
reviewandmeta‐analysisof10prospectivecohortstudiesshoweda25%reducedriskof
incidenceormortalityfromIHDinvegetarianandvegandietsbutnotoftotalCVDand
strokemortality[48].CVDandstrokemortalityoutcomesmaybeinfluencedbylifestyle
factorsotherthandietandbyaccesstocardiovascularhealthcare.
4.2.Type2Diabetes
Observationalstudiesinavarietyofpopulationshaveconsistentlyshownthat
comparedtonon‐vegetarians,thosefollowingavegetarianorvegandiethavea
significantlylowerriskofT2D[41,49–53].A2017systematicreviewandmeta‐analysisof
14studiesfoundapooledoddsratiofordiabetesinvegetariansvs.non‐vegetariansof
0.73[54].A2020systematicreviewsimilarlyfoundthatavegandietwasassociatedwith
lowerprevalenceorincidenceofT2D,althoughinsomestudiesitwasnotpossibleto
determineifthebenefitswereduetothevegandietaloneorcombinedwithotherhealthy
lifestylehabits[55].
A2018systematicreviewofnineRCTsfoundthat,comparedtocontroldiets
(includingthoseofseveraldiabetesassociations),plant‐baseddietswereassociatedwith
significantimprovementinemotionalwell‐being,physicalwell‐being,depression,quality
oflife,generalhealth,HbA1clevels(ameasureoflong‐termbloodglucoselevels),weight,
andtotalandLDLcholesterollevels[56].Anearliersystematicreviewandmeta‐analysis
ofsixstudiesfoundthattheconsumptionofvegetariandietswasassociatedwitha
significantreductioninHbA1ccomparedtocontroldiets[57].Similarly,areductionin
HbA1chasbeenobservedwithplant‐baseddiets,includingvegetarian,vegan,
Mediterranean,andDietaryApproachestoStopHypertension(DASH)diets,compared
tocontrolorconventionaldiets[58].
Thereareseveralpossibleexplanationsforthebenefitsofplant‐baseddietsfor
diabetespreventionandmanagement.Comparedtomostwesterndiets,vegetarianand
vegandietsaregenerallyhigherindietaryfiberandarelikelytoincludemorewhole
grains,legumesandnuts,allofwhichhavebeenassociatedwithareducedriskofT2D
[59].Thereisalsoevidenceforaninverseassociationbetweenhigherintakesofgreenleafy
vegetablesandfruitandtheriskofT2D[60–63].
Theabsenceorlimitedintakeofanimalproteinandredmeatalsolikelyplaysarole.
Atleast25studieshavebeenpublishedassessingtherelationshipbetweenmeatintake
andT2Drisk,withthemajorityshowingapositiveassociationbetweenredmeatand/or
processedmeatintakes.A2013meta‐analysisfoundanassociationbetweenhigher
intakesoftotalmeat,unprocessedredmeat,andprocessedmeatandT2Drisk[64].There
isalsoconsistentevidenceforanassociationbetweentotaldietaryhemeironintakeand
hemeironintakefromredmeatandriskofT2D,andhighserumferritinlevelsare
associatedwithinsulinresistanceandT2Drisk[65].A2019meta‐analysisofprospective
cohortstudieslookingatdietaryproteinintakeandsubsequentriskofT2Dfoundhigh
totalproteinandanimalproteinintakestobeassociatedwithanincreasedriskofT2D,
whileamoderateplantproteinintakewasassociatedwithadecreasedrisk[66].Anearlier

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systematicreviewandmeta‐analysisof13RCTsinpeoplewithdiabetesfoundthat
replacinganimalproteinwithplantprotein(around35%oftotalprotein/day)resultedin
significantreductionsinHbA1c,fastingglucose,andfastinginsulinlevelscomparedto
controlgroups[67].
ExcessweightisasignificantcontributortoinsulinresistanceandT2Drisk,and
weightlossisakeycomponentofthemanagementofT2D[68].Followingavegetarianor
vegandiet,oneislesslikelytobeoverweight[69].
4.3.Cancer
Eachoftheplantfood‐groupshasshownthattheypossesschemo‐protective
properties.Systematicreviewsandmeta‐analyseshaveshownthatanincreasednut
consumptionwasassociatedwithbothadecreasedriskofallcancerscombined[70]and
decreasedcancermortality[71].Inthesamemanner,anincreasedintakeoffruitsand
vegetablesandofwholegrainswasshowntodecreasetheriskoftotalcancerincidence
[72]andtotalcancermortality[73],respectively.Furthermore,ahigherintakeoflegumes
(beansandlentils)wasassociatedwithadecreaseintheriskofgastro‐intestinalcancers
andallcancersitescombined[74].Manyplantfoodsarerichinhealth‐promoting
phytochemicals,someofwhichhavebeenshowntobeusefulinthetreatmentofhuman
cancer[75,76].
Ontheotherhand,theconsumptionof100–120g/dayofredmeatsignificantly
increasedtheriskofmanycancers(comparedtoeatingnomeat):11%forbreastcancer,
17%forcolorectalcancer,and19%foradvancedprostatecancer[77].Fortheconsumption
of50g/dayofprocessedmeat,theriskwasincreased4%fortotalprostatecancer,9%for
breastcancer,18%forcolorectalcancer,19%forpancreaticcancer,and8%forcancer
mortality[77].IntheFrenchNutriNet‐Santécohortstudy,redmeatintakewasassociated
withincreasedriskofoverallcancers(HR1.31)andbreastcancer(HR1.83),butnot
prostatecancer[78].IntheNationalInstitutesofHealth(Rockville,MD,USA)—AARP
DietandHealthStudycohortofhalfamillionpeople,aged50to71yearsatbaseline,
higherredandprocessedmeatintakeswereassociatedwithmodestincreasesintotaland
cancermortality[79].
Withtheeliminationofmeatandagreateruseofprotectiveplantfoods,vegetarians
mayhaveareducedriskofcancer.EpidemiologiccohortstudiesintheU.S.andUKhave
providedhigh‐qualityevidenceregardingtheassociationofvegetariandietarypatterns
withcancerrisk.IntheUS‐basedAHS–2,veganshadloweroverallcancerriskcompared
tonon‐vegetarians(HR0.84);overallcancerriskforlacto‐ovovegetarianswasnot
significantlydifferentfromnon‐vegetarians[80].Vegansshowedalowerriskofprostate
cancer(HR0.65)[81]andalower(butnotstatisticallysignificantlylower)riskofbreast
cancer[82].Neitherlacto‐ovo‐vegetariansorveganshadasignificantlylowerriskof
colorectalcancer[83].
IntheUK‐basedEPIC‐Oxfordstudy,comparedwithmeateaters,vegans(HR0.82)
andlacto‐ovovegetarians(HR0.90)hadlowerriskofallcancerscombined[84].For
prostatecancer,whilevegans(HR0.61)andvegetarians(HR0.86)hadlowerrisk,they
werenotsignificantlydifferentfrommeateaters[84].Forcolorectalcancerandfemale
breastcancer,riskforthevegetariangroupsagaindidnotsignificantlydifferfrommeat
eaters[84].IntheUKWomen’sCohortStudy,comparedwithredmeateaters,theriskof
breastcancerforvegetarianswasnotsignificantlylower(HR0.85)[85].
Takenasawhole,suchresultsseemtosupporttheideathatvegetarians(including
vegansandlacto‐ovovegetarians)haveamodestbutpotentiallyimportantreducedoverall
cancerriskcomparedtotheirnon‐vegetariancounterparts.Findingsforcommonindividual
cancers(colorectal,prostate,breast)arelessconsistentandwarrantfurtherstudy.
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4.4.OverweightandObesity
Over70%ofadultsintheU.S.areoverweightorobese[86],andtrendsshowthat
overweightandobesityareincreasingworldwide[87].Observationalstudiesshowthat
vegansandvegetarianstypicallyhavealowerBMIthanomnivores[88,89],and
vegetariandietsorplant‐basedtypedietarypatternsareprotectiveagainstadultweight
gainand/ortheriskofoverweightorobesity[90,91].Veganstypicallyhavethelowest
BMIorlowestprevalenceofoverweightorobesityinstudiesthatcomparemultiple
dietarypatterns,includingvegetariansandomnivores[88,92].Goggaetal.noted
differencesinpercentbodyfatbetweenvegans,lacto‐ovo‐vegetarians,andomnivores,
eventhoughallgroupBMIvalueswerewithinthenormalrange[93].Interventionsusing
vegan[94–99],vegetarian[97,100],orwhole‐foodplant‐baseddietary[101]treatments
havebeenfoundtolowerBMI,weight,orfat‐masscomparedtosubjectsonameat‐based
diet.A4.8%weightlosswasreportedforoverweightandobesesubjectsrandomizedtoa
veganorvegetariandietfor2months,comparedtoa2.2%lossseeninthoseconsuming
anomnivorousdiet[97].Weightlossof3to5%isclinicallymeaningfulandmay
contributetochronicdiseaseriskfactorreduction[102].
Thequalityoftheplant‐baseddietisalsoanimportantconsideration.Subjectswho
adheretoahealthyplant‐baseddietarereportedtohavealowerBMI,waist
circumference,andvisceralfatthanthosewhoadhereto‘unhealthy’plant‐baseddiets
[103,104].Researchershavenotedthatdietqualitymaybemoreimportantthandietary
patternswhencomparingvegans,vegetarians,andomnivores,astheadiposityvaluesdid
notdiffersignificantlybetweenthesegroups[105].Theweightlossexperiencedona
hypocaloriclacto‐ovo‐vegetariandietwassimilartothatobservedwithahypocaloric
Mediterraneandiet[106].
Mechanismsthatexplaintheweightmanagementbenefitsofplant‐baseddiets
includerelativelyhigherfiber,fruit,andvegetableconsumptioncomparedtoomnivorous
diets[88,107].Thisfoodpatternmayleadtobeneficialalterationstoappetitehormones
[93,108]andthegutmicrobiota[109],bothofwhichmayhaveanimpactonbodyweight.
4.5.BoneHealth
Healthybonesrequireavarietyofessentialnutrientsandhealthylifestylepractices
tomaximizepeakbonemassduringgrowthandminimizebonelosslaterinlife[110].
WhilecalciumandvitaminDarewellrecognizedasimportantcontributorstobone
health,othernutrients,includingmagnesium,potassium,vitaminK,vitaminC,andzinc,
aswellasbioactivecompoundsfoundinfruitsandvegetables,havebeensuggestedas
contributingtobonehealthand/orreducedriskoffracture[111–114].Somehavereported
greaterbenefitfromvegetables,especiallycruciferousandalliumvegetables,thanfrom
fruit[115,116].
Therelationshipofproteinintaketobonestatusiscomplex.Earlierstudiesshowed
highintakescausealossofcalcium,whilearecentreviewfound“noadverseeffectsof
higherproteinintakes”andsomepositivetrendsatmostbonesites[117].Arecentreview
andmeta‐analysisfoundnodifferencebetweensoyandanimalproteinonbonemineral
density(BMD)andcertainmarkersofboneturnover[118].Otherssuggestthelowacid
loadofvegetariandiets,partlyduetothepotassiumandmagnesiumcontentfroman
increasedfruitandvegetableintake,isbeneficialtobonehealth[119].Someelderly
vegetariansandafewvegansmaynotconsumesufficientproteinformaintainingoptimal
bonehealth[114,120,121].
Theimpactofavegetariandietonbonehealthhasmanydimensions.Reportscan
varyconsiderablyinstudydesign,populations,andconclusions.Somefindsignificantly
lowerBMDinvegetarians,especiallyvegans,whichcouldincreasefracturerisk[122],
whileothersseenodifferenceinbonehealth,providedthatcalciumandvitaminDis
adequate[123],andconcludethatvegetarianfoodcanprovideasolidfoundationfor
healthybonesandpreventingfractures[124].

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
AlargeprospectiveUKstudyfoundthatfisheatersandvegetarianshadahigher
riskofhipfracturescomparedtomeateaters,whileveganshadagreaterriskoftotal,hip,
leg,andvertebralfractures[125].Someofthedifferencesmayhavebeenpartlydueto
lowerBMIandpossiblylowerintakeofcalciumandproteininthevegans.
Asystematicreviewofsome20studiesinvolving37,134subjectsfoundvegetarians
andveganshadlowerBMDatthefemoralneckandlumbarspinecomparedtoomnivores
[126].Theeffectwasgreaterinveganswhoalsohadhigherfracturerates[127,128].
Anotherreviewconcludedthatthebalancebetweenprotectivefactorsinvegetarianand
vegandietsandpotentialnutrientshortfallsmayleavevegetarians,andespeciallyvegans,
atincreasedriskofbonelossandfractures[129].Potentialnutrientshortfallscanbe
remediedbyappropriatefoodselections(includingfortifiedfoods)containingcritical
nutrientsorbytakingsupplements.Moreresearchdataonthebonehealthofvegansare
neededbeforedefinitiverecommendationscanbemade.
5.EatingDisorders
Previoususeofavegetarianorvegandietapparentlydoesnotincreasetheriskof
developinganyeatingdisorder,suchasanorexianervosa,bulimianervosa,andbinge
eatingdisorder[130,131].Thosewithpreexistingdisorderedeatingtendenciesmayselect
vegetarianorpartiallyvegetariandietsasawaytolimitfoodintakeinasocially
acceptablefashion[130,132].Semi‐vegetariansappeartobeathigherriskfordeveloping
eatingdisordersthanvegetariansandvegans[130,133].Thosevegetarianswhose
motivationisweightcontrolreportmoresymptomsofdisorderedeatingthandothose
withothermotivations[134].Commonlyusedassessmenttoolsmayincorrectlyassess
dietaryrestraintoreatingdisorderpsychopathologyinvegetarians[130].
6.Plant‐BasedDietsandtheGutMicrobiome
Thehumangutmicrobiotaisahighlycomplexcommunityofsome1014
microorganisms.Diethasasignificantimpactuponthemicrobiotacompositionand
function[135,136].Themicrobiomehasaprofoundimpactonone’spersonalhealthand
wellbeing[137].Manipulatingthegutmicrobiotahasbeenviewedasawaytomodulate
theriskofchronicdiseasessuchasobesity,T2D,cancer,andCVD[135,137].
Gutmicrobiotahaveamajorroleinthefermentationofnondigestiblecarbohydrates,
namelyresistantstarch,soluble/insolubledietaryfiber,includingplantwall
polysaccharidesandoligosaccharides.Fermentationofthesenondigestiblecarbohydrates
isassociatedwithahigherabundanceofmicrobesthatproducebutyrateandothershort‐
chainfattyacids,whichhaveananti‐inflammatoryfunction,strengthentheintestinal
barrierfunction,andimproveoverallguthealth[138–141].Forexample,theconsumption
offiber‐richfoodssuchasbarley,wheatbran,brownrice,andotherwholegrains,aswell
asfructo‐oligosaccharidesandotherprebiotics,arereportedtoincreasebutyrate‐
producingmicrobes[137,142–146].Vegetarianswouldbeexpectedtohaveanincreased
abundanceofthesemicrobes,astheirfiber‐richdietsaretypicallyhighinwholegrains,
fruits,vegetables,nuts,andlegumes[107].
Theseplantfoodsalsocontainpolyphenols—lignans,isoflavones,anthocyanins,and
flavonols—inadditiontootherphytochemicalssuchascarotenoidsandphytosterols
[147–149].Thesearemetabolizedintobioactivecompoundsbyvariousmicrobes[150],
somewithhealthbenefitsandanti‐inflammatoryorantioxidantactivity.Phytochemicals
increasebeneficialbacteria,includingLactobacillusandBifidobacterium,whicharethe
primaryspeciespresentinprobioticsupplementsthataretakentoimproveguthealth
[151],inadditiontosomebutyrateproducers[150].Amongfiber‐richplantfoods,nutsin
particular(walnuts,almonds,pistachios)havebeenfoundtohaveprebioticeffectsand
areassociatedwithincreasesinbutyrate‐producingmicrobesandotherbeneficial
microbes[152].Hence,thegutmicrobialcompositionisgreatlyinfluencedbydietaryfiber
aswellasbypolyphenolsandotherphytochemicalsandtheirmetabolites,allofwhich
aremorehighlyconsumedbyvegetarians.

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Studieshavesupportedthevalueoftwoso‐calledenterotypes,orclustersofmicrobes
drivenbydistinctgenera,indistinguishingdietarypatterns.Accordingly,Bacteroidesare
associatedwithanimalfatandhigh‐proteindiets[153–157],andPrevotellaareassociated
withfiber‐richfoodsandcarbohydrates,typicalofaplant‐baseddiet[158–160].Higher
abundanceofPrevotellaandotherpolysaccharide‐degradingorpotentialbutyrate‐
producingmicrobeshasbeenseenparticularlyinagrarianculturessuchasthosein
Tanzania,thePeruvianAmazon,andBurkinaFaso,comparedtoU.S.orWestern
populations,reflectingthehigherconsumptionoffiber‐richplantfoodsbythesesocieties
[160–162].Hence,enterotypesmayhavesomeutilityindistinguishingplant‐andanimal‐
baseddiets.Plant‐basedandhigh‐fiberdietsarealsoassociatedwithincreasesinthe
Bacteroidetesphylum[160,162],ortheBacteroidetes/Firmicutesratio,aswellasmicrobial
richness/diversity[142,155,160,162–164],incontrasttodietshighinfat[165–169].Thisis
relevantinthatvariousmicrobesfromtheBacteroidetesphylumencodecarbohydrate‐
activeenzymes(CAZymes)necessaryfordegradingindigestiblecarbohydrates[139],and
theBacteroidetes:Firmicutesratiomayhaveimplicationsforobesityandmetabolicdiseases,
althoughtherelationshipisnotclearasfindingshavebeeninconsistent[170,171].
Differencesingutmicrobialcompositionarenotalwaysobservedincross‐sectional
studiescomparingvegansorothervegetarianswithnon‐vegetarians[172].IntheAHS‐2
cohort,onlysubtledifferenceswerenotedinthemicrobiome[173].However,vast
differenceswerediscoveredintheplasmametabolome,withvegansshowinghigher
abundanceofanti‐inflammatoryplant/polyphenolormicrobial‐relatedmetabolites[174].
Non‐vegetariansontheotherhandmayhavehigherabundanceofaminoacidsandlipids
conceivablyassociatedwithcardiometabolicphenotypes[174–176].Intestinalmicrobiota
convertcholineandL‐carnitine,derivedfrommeat,fish,dairy,andeggs,into
trimethylamine,whichisoxidizedbythelivertotrimethylamineN‐oxide(TMAO),apro‐
inflammatorycompoundthathasbeenassociatedwithincreasedcardiometabolicrisk
[177–180].Thus,itmaybethatmicrobialfunctionismorerelevantthancomposition,with
metabolicprofilesshowingmuchgreaterdifferences,reflectingphenotypicchanges.
Therearephysiologicalconsequencesofdiet‐inducedshiftsinthemicrobiome.Low
consumptionofplant‐basedfoodsmayleadtoincreasedpenetrationoftheintestinal
barrier,asalow‐fiberdiettriggersashiftfromfiber‐degradingtomucus‐degradingbacteria
[181].Thisinturncouldpromoteahyperactiveimmuneresponse,conceivablywiththe
productionofpro‐inflammatorymetabolitesthatfueldiseaseprocesses[182].However,
muchremainstobeunderstoodabouthowvegetarianandplant‐baseddietarypatterns
impactthemicrobiomeandassociatedmetabolicresponsestoinfluencediseaseprocesses.
7.Plant‐BasedDietsandtheLifeCycle
Vegetarian,includingvegan,dietscansatisfythenutritionalrequirementsofall
stagesofthelifecycle.Theycanpromotenormalgrowthanddevelopmentininfancy,
childhood,andadolescenceandmeettheneedsforenergyandnutrientsoftheselifecycle
stagesaswellasthoseofpregnancy,lactation,andolderadulthood.
7.1.PregnancyandLactation
Vegetariandietscaneffectivelymeetenergyandnutrientneedsinpregnancyand
lactation[183,184].Severalreviews,whilenotingthelimitedamountofinformationabout
vegetarian,includingvegan,dietsinpregnancy,haveconcludedthat,withadequate
nutrientintake,thesedietsaresafeinpregnancy[183,185].Whenfoodaccessis
satisfactory,infantbirthweightsandthedurationofgestationaresimilarinvegetarian
andnonvegetarianpregnancy[186,187].Somestudiesreportthatvegetariansaremore
likelytohaveinfantswhoaresmallfortheirgestationalage[188–190].Thisfindingmay
beduetolowermeanpre‐pregnancyBMI,lowerweightgain,orinadequateweightgain
inpregnancy.Well‐nourishedvegetariansproducenutritionallyadequatebreastmilkthat
supportsinfantgrowthanddevelopment[191].

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Healthbenefitsofvegetariandietsinpregnancyincludealowerriskofexcessive
weightgainandhigherfiberandfolateintakes[188,192,193].Dietarypatternsthatare
highinplantfoodsareassociatedwithareducedriskofgestationaldiabetesmellitus,
hypertensivedisordersofpregnancy,andpretermbirth[194].
Nutrientrequirementsinvegetarianpregnancyandlactationgenerallydonotdiffer
fromthosefornonvegetarians[195].Vegetariansmayespeciallybenefitfromguidanceon
sourcesofiron,zinc,vitaminB12,iodine,anddocosahexaenoicacid(DHA).Although
ironabsorptionincreasesinpregnancy[196],ironneedsarehigh,soiron‐richfoodsand
low‐doseironsupplementsarerecommendedforallwomen[197,198].Theincreasedneed
forzinccanbemetthroughacombinationofincreasedintakeandabsorption[199].
Phytate’sinhibitoryeffectonzincabsorptionismarkedlyreducedinlatepregnancyand
earlylactation[200].Inadditiontotheuseofiodizedsalt,a150μg/diodinesupplement
isrecommendedforallpregnantandlactatingwomen[201].
Duringpregnancy,bloodDHAconcentrationsareoftenlowerinvegetariansthanin
nonvegetarians[202];cordbloodDHAislowerininfantsofvegetarians[202].Breastmilk
DHAconcentrationsofvegetariansandvegansarelowerthanworldwideaverages[203].
DHAoromega‐3supplementationisassociatedwithgreatergestationaldurationanda
reducedriskofpretermbirth[204,205].SupplementalDHAderivedfrommicroalgae
shouldbeusedinvegetarianpregnancyandlactation[195].
AdequatevitaminB12intakeisespeciallyimportantduringperiodsofgrowthsuch
aspregnancyandbreastfeeding.Infantsborntolong‐termveganmothersandwhoare
breastfedareatriskofB12deficiency.Thisisespeciallytruewhenthemother’sdietisnot
well‐supplemented.SymptomsofB12deficiencyinbreastfedinfantsandsmallchildren
fedavegandietincludedevelopmentaldelayorpsychomotorregression,lethargy,
anemia,neurologicalissues,andfailuretothrive[206].Pregnantandlactatingvegetarians
shouldconsumereliablesourcesofvitaminB12,suchassupplementsand/orfortified
foods,onadailybasis[195].
7.2.Infants,Children,andAdolescents
Vegetarian,includingvegan,dietsthatarenutritionallyadequateareappropriatefor
useininfancy,childhood,andadolescenceandsupportnormalgrowth[184,207,208].
Healthbenefitsofvegetariandietsinchildhoodandadolescenceincludethepotentialfor
exposuretoawidevarietyofplantfoods,lowerriskforchildhoodobesity[209],and
higherconsumptionoffruitsandvegetables[210,211].Veganchildrenappeartohave
lowerintakesoftotalandsaturatedfatandcholesterolcomparedtonon‐veganchildren
[211].Alow‐fatvegandiethaseffectivelytreatedchildrenwithobesityandelevatedblood
pressure[212].
Exclusivebreastfeedingisrecommendedforinfantsforthefirst6monthsafterbirth,
withbreastfeedingcontinuinguntilatleast12monthsofage[213].Ifbreastfeedingor
exclusivebreastfeedingisnotpossible,commercialinfantformulashouldbeusedasthe
primarybeverageforthefirstyear.Plantmilks,unmodifiedcow’smilk,othermilks,and
homemadeformulasshouldnotbeusedtoreplacebreastmilkorformuladuringthefirst
year.Standardpracticesshouldbeusedwhenintroducingcomplementaryfoodsto
vegetarianinfants.Vegetableproteins,suchaspureedbeansortofu,areusedinplaceof
pureedmeats.Afterthefirstyear,iftoddlersaregrowingnormallyandeatingavariety
offoods,fortifiedsoyorpeaproteinmilkordairymilkcanbestarted[195].
Severalnutrientsrequirespecialattentionintheplanningofnutritionallyadequate
dietsforyoungvegetarians,includingiron,zinc,iodine,andvitaminB12;calciumand
vitaminDmayalsorequireattention,dependingondietarychoicesandotherfactors.
Proteinrecommendationsforveganchildrenmaybesomewhathigherthanstandard
recommendationsbecauseoffactorsincludingproteindigestibilityandaminoacid
composition[195].Proteinneedsofvegetarianorveganchildrenandadolescentsare
generallymetwhentheirdietscontainadequateenergyandavarietyofplantprotein
sources.Deficienciesofironandzincarerarelyseeninvegetarianchildreneatingvaried

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diets[207].Zincsupplementationmaybeneededwhencomplementaryfoodsare
introduced,iffoodsaremainlythosewithlowzincbioavailability[214].Ironandzinc
statusininfants,children,andadolescentsshouldbemonitored,andfortifiedfoods
and/orsupplementsusedasneeded.Iodizedsaltisareliablesourceofiodineforchildren
andteens.IfmaternalvitaminB12intakeorstatusareinadequate,breastfedinfants
shouldbegivensupplementalvitaminB12[206].Vegetarianchildrenandadolescents
shouldusevitaminB12‐fortifiedfoodsorsupplementstosupplyadequatevitaminB12.
Calciumsourcesforchildrenandadolescentsincludefortifiedplant‐basedmilks,green
leafyvegetables,anddairyproducts.
7.3.OlderAdults
Olderadultsgenerallyhavedecreasedenergyrequirements,althoughnutrient
requirementsareoftensimilarto,orhigherthan,thoseofyoungeradults.Theselectionof
nutrient‐densedietsisespeciallyimportantforolderadults.Limitedresearchindicatesthat
nutrientintakesofoldervegetariansarecomparabletothoseofoldernon‐vegetarians[195].
Recommendationsforcalcium,vitaminB6,andvitaminDarehigherforolderadults
[215,216].Thereissomeevidencethatproteinneedsincreaseaswell[217].Higherprotein
foodssuchassoyproducts(includingtofu,soybeverage,soyyogurtalternative,etc.),
legumes,nutsandseeds,andmeatanalogsshouldbeusedtwotothreetimesadayby
oldervegetarians.VitaminB6recommendationsforallolderadultsarehigherdueto
decreasedabsorptionandalterationsinmetabolism[216].Vegetariansgenerallyhave
adequateintakesofvitaminB6.Sourcesincludepotatoes,bananas,fortifiedbreakfast
cereals,andspinach.Severalfactorsincreaseolderadults’riskforvitaminDinsufficiency,
includingreduceddermalandrenalsynthesis[218,219],inadequatedietaryintake,and
limitedsunexposure.Fortifiedfoodsand/orsupplementsmaybeneededforolderadults
tomeetrecommendationsforcalciumandvitaminD.
ThemaincauseofvitaminB12deficiencyinolderadultsisimpairedabsorptionof
vitaminB12fromfoods[220].AbsorptionofpurifiedvitaminB12fromfortifiedfoodsand
supplementsisnottypicallyimpaired,sorecommendationscallforolderadultstouse
fortifiedfoodsandsupplementsastheirprimarysourcesofvitaminB12[216].
8.AthleticPerformance
Vegetariandietscanmeettheneedsofathletesatalllevels,fromrecreationaltoelite
athletes[221,222],andhavebeenfollowedbyathletesthroughouthistory[223].Whilea
nutritionallyadequateplant‐baseddietisthoughttohelpoptimizetrainingand
performance,dueinparttoitshighcarbohydrate[223–225]andhighphytochemical
content[225],limitedevidencefromwell‐controlledstudiessuggeststhatvegetariandiets
neitherenhancenorimpairperformance[225].Additionalresearchisneededtodetermine
whethersuchdietsenhancerecoveryandattenuatetheoxidativedamageand
inflammationthatoccurwithheavytraining.
Nutritionrecommendationsforathletesshouldconsidereachathlete’straining
volume(intensityandfrequency),sport,season,performancegoals,andfoodpreferences.
Vegetariandietsthatmeetenergyneedsandcontainavarietyofplant‐basedprotein
sources,includingsoyfoods,driedlegumes,nuts,seeds,quinoa,andothergrains,can
provideadequateproteintosupportmosttrainingneeds.Thereissomeevidencethat
plant‐derivedproteinsresultinlowerpost‐prandialmuscleproteinsynthesisresponses
comparedwithequivalentamountsofanimal‐derivedproteins[226];thisresponsemay
beimprovedbyconsumingblendsofdifferentplant‐derivedproteins[226].Milkandeggs
[227–229]cansupplementplant‐basedsourcesforvegetarianathletes.
Dependingonfoodpreferences,athletesneedtoensuretheyconsumeadequate
amountsofthenutrientsthatareeitherfoundlessabundantlyinvegetarianfoodsorare
lesswellabsorbedfromplantscomparedtoanimalsources.Thesenutrientsinclude
calcium,iron,zinc,iodineandvitaminB12.Forexample,femaleathletesandendurance
athletesshouldensuresufficientconsumptionofiron‐richplantfoodsalongwithdietary

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factorsthatenhanceratherthaninhibitironabsorption[230–232].Femaleathleteswith
restrictedintakeandamenorrhea(i.e.,lowenergyavailability)[233]mayrequire
additionalcalcium(1500mg/dayalongwith1500–2000IUvitaminD)tooptimizebone
health[234].MaintainingadequatevitaminDstatusisimportantforathletesduetoits
roleinimmunefunction,inflammatorymodulation,physicalperformance,andoverall
health[235–238].Vegetarianathletesmayhavelowerbloodandmusclecreatinineand
carnitineconcentrations[239–242]comparedtoomnivoresduetolowerdietaryintake.
Athletesparticipatinginresistancetrainingandboutsofhigh‐intensityexercisemay
benefitfromcreatinesupplementation[243],butthereisnorecognizedbenefittocarnitine
supplementation.Vegetarianathletes,likemostothers,maybenefitfromeducationabout
foodchoicestooptimizehealthandpeakperformance[244].
9.NutrientsofConcerninaPlant‐BasedDiet
9.1.Calcium
Inadditiontoitsroleinbonemineralization,calciumisrequiredforbloodclotting,
musclefunction,nervetransmission,hormonerelease,intracellularsignaling,and
regulatingkeyenzymes[245].Typically,vegansconsumesubstantiallylesscalciumthan
othervegetariansandomnivores[192,246].Whencalciumintakesarelow,thebodycan
compensatesomewhatbyincreasingthefractionalcalciumabsorption[247]and
decreasingurinarycalciumexcretion[215].However,anyone,includingalltypesof
vegetarians,withinadequatecalciumintakeneedstoconsistentlyusecalcium‐fortified
foods,suchasfortifiedbreakfastcereals,fortifiedfruitjuices,andfortifiedplant‐based
beverages,ortakeacalciumsupplement,tomeettheircalciumneeds.Vegandietsinthe
UKhavebeenassociatedwithaclinicallysignificantincreasedriskoffracturewhenthe
calciumintakewasinadequate[248].
Phyticandoxalicacidsinplantfoodsarebothinhibitorsofcalciumabsorption.The
calciumabsorptionfromoxalate‐richvegetables(spinach,Swisschard)maybeaslow5%;
frombeans,almonds,tahini,andfigs20–25%;fromdairyproducts32%;fromsoy
products(tofu,fortifiedsoybeverages),itissimilartodairymilk;andfromlow‐oxalate
vegetables(kale,Chinesecabbage,broccoli,bokchoy,etc.)50–60%[249–251].Boilingcan
reduceoxalatecontentingreenleafyvegetables[252].Avegetariandiet,withitshigh
intakeoffruitandvegetables,isrichinanti‐inflammatoryphytonutrients,specifically
carotenoidsandflavonoids,andpotassiumandmagnesium.Carotenoidsandflavonoids
areassociatedwithanimprovedBMDandlowerbonefractures[253–256].
Comparedtoavegetariandiet,consumingananimalproteindietisassociatedwith
anincreasedlossofurinarycalcium[257].
9.2.Iron
Inadditiontoitsabilitytotransferoxygenbymeansofhemoglobinandmyoglobin,
ironfunctionsasaco‐factorformanyimportantenzymes(suchasmyeloperoxidase,
importantforimmunefunction)andhasaroleinthyroidhormonesynthesisandamino
acidmetabolism[245].Sincehemeironisgenerallybetterabsorbed(15–30%)thannon‐
hemeiron(typically5–10%),omnivoresareassumedtohavebetterironstatus.However,
vegetarianswhoeatavariedandwell‐balanceddietdonotappeartobeatanygreater
riskofiron‐deficiencyanemiathanomnivores[258,259].Hemoglobinlevelsofthetwo
dietarygroupsnormallyshownosignificantdifferences[259,260].Additionalstudiesof
irondeficiencyinvegetariansareneededbeforedefinitiveconclusionscanbereached.A
varieddietthatisrichinwholegrains,legumes,nuts,seeds,driedfruits,iron‐fortified
cerealproducts,andgreenleafyvegetablesprovidesanadequateironintake.Vegetarian
dietsgenerallycontainasmuchormoreironthanomnivorediets[92,195].
Non‐hemeironabsorptionissignificantlyaffectedbyseveraldietarycomponents
[261,262].VitaminC,otherorganicacids(citric,malic,lactic,tartaricacids),anderythorbic
acid(anantioxidantusedinprocessedfood)allenhanceabsorption[196,230,259,263,264].

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Plantferritin,foundinsoyandotherlegumes,isaneasilyabsorbedsourceofiron(22–
34%).Whilephytates(foundinlegumes,nuts,andwholegrains)caninhibitnon‐heme
ironabsorption,theirinhibitoryeffectisdiminishedbybaking,soaking,leavening,and
germination[184,265].Furthermore,theoveralllong‐termeffectofenhancersand
inhibitorsofironmaybelessimportantthanoncethoughtwhenthefoodsareeatenas
partofawholediet[266,267].
Absorptionofnon‐hemeironisalsoinverselyrelatedtothebody’sironstatus[196].
Whenstoresarelowandtheneedforironincreases,compensatorymechanismsfacilitate
greaterabsorptionofiron.Absorptioncanbeaslowas2–3%inpeoplewithgoodiron
storesbutashighas14–23%inpeoplewithlowironstores[268].
Humanshavealimitedabilitytoexcreteexcessstorediron[258],soconsuminglarge
amountsofhemeironmaybeunhealthyduetoitspro‐oxidantnature.Consumptionof
hemeironhasbeenassociatedwithanincreasedriskofchronicdiseasessuchasdiabetes,
metabolicsyndrome,andcolorectalcancer[269–272].Vegetarianstypicallyhavelower
ironstores(asreflectedinlowerserumferritinlevels),whichmaybeanadvantageas
lowerserumferritinlevelsmaybeassociatedwithimprovedinsulinsensitivityand
reducedriskofT2D[258,273].
Ironabsorptionfromanomnivorousdietisclaimedtobeabout18%,whereasfora
plant‐baseddietitissaidtobeabout10%[196].Hence,thecurrentDietaryReference
Intake(DRI)forironforvegetarianshasbeenset1.8timeshigherthanthatfornon‐
vegetarians.Thisincreasedrequirementisbasedonlimitedresearch,whichhasbeen
unabletoaccuratelymeasureadaptiveabsorptionratesofnon‐hemeironinvegetarians
[267,274].Furtherresearchisneededtoreassesstheironrequirementrecommendedfor
vegetarians[232].
9.3.Zinc
Zincactsasacoenzymeformultipleenzymesinvolvedwithgrowth,immunity,
cognitivefunction,bonefunction,andregulationofgeneexpression[275,276].Zinc
deficiencycausesstuntedgrowth,poorappetite,dermatitis,alopecia,endocrine
dysfunction,andimpairedimmunity[276].Zincdeficiencyisnotanymorecommonly
seeninvegetariansthaninnon‐vegetarians[277].Zincintakeandserumlevelsfor
adolescentandadultvegetariansindevelopedcountriesarethesameorslightlylower
thanforomnivores,butwithinthenormalrange[214,231,275,278,279].Indeveloping
countries,vegansandvegetariansaremorelikelytoshowmarginalzincstatus[278].
Thebioavailabilityofzincfromplantfoodsmaybereduced.However,zinc
absorptionandretentioncanberegulatedbyhomeostaticmechanisms,adaptingtolower
intakesbyreducinglossesandincreasingabsorption[275].Duringperiodsofhigh
demand(pregnancy,infancy),absorptionbecomesmoreefficient[280].
Phytatesincerealsandlegumeslowerabsorptionofzinc,butleavening,soaking,
fermenting,orsproutingreducesthephytatelevelsandmakeszincmorebioavailable
[281].Sulfur‐containingaminoacidsandorganicacidsinavarietyofplantfoodswillalso
enhancezincabsorption[279,282].
Vegetarianfoodsourcesforzincincludenuts,seeds,wholegrains,legumes,tofu,
tempeh,anddairyproducts[283].Theuseofsupplementsandfortifiedfoods(suchas
fortifiedbreakfastcereals)maybenecessaryforveryrestrictedvegandiets[214,246].
9.4.Iodine
Iodineisessentialforthyroidhormones,whichregulatemetabolicactivity.Iodineis
especiallyimportantinpregnancyforfetaldevelopmentandduringearlychildhood.
Iodinedeficiencyinchildhoodcanpreventchildrenfromattainingtheirfullphysical
potentialandintellectualcapacity[284].
Majordietarysourcesofiodineincludeiodizedsalt,seafood,anddairyproducts
[284].Theiodinecontentofseaweedsanddairyproductscanvarywidely[195,285].Sea
salt,Himalayansalt,andthesaltusedinprocessedfoodstypicallydonotcontainiodine

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[195].Althoughfoodssuchassoybeans,cruciferousvegetables,andsweetpotatoes
containnaturalsubstancesthatinterferewithiodineuptakebythethyroid,thesefoods
havenotbeenassociatedwiththyroiddysfunctioninhealthypeople,providediodine
intakeisadequate[196,286].
Veganswhodonotuseiodizedsaltand/orseavegetablesmayhavelowiodine
intakesandmaybeatriskforiodinedeficiency[287,288].
9.5.VitaminB12
VitaminB12isrequiredforredbloodcellformation,DNAsynthesis,homocysteine
metabolism,andthemyelinationandfunctionofthecentralnervoussystem[289].
VitaminB12deficiencyisnotuncommonamongtheelderlyandunsupplementedvegans.
Itcanmanifestitselfwithconsequentialhematologicalandneurologicalchanges.
Typically,themeandietaryintakeofvitaminB12ofvegansfallswellbelowtheDRI,while
thatoflacto‐ovo‐vegetariansmaybemarginal,dependingontheuseofdairyproducts
[246,290,291].VegansmustobtaintheirvitaminB12eitherfromregularuseofvitamin
B12‐fortifiedfoods,suchasfortifiedplant‐basedbeverages,fortifiedbreakfastcereals,
fortifiedvegetarianmeatanalogs,orfromaregularvitaminB12supplement.Unfortified
plantfoodssuchasfermentedsoyfoods,leafyvegetables,seaweeds,mushrooms,and
algae(includingspirulina)donotcontainsignificantamountsofactivevitaminB12to
providedailyneeds[292].Furthermore,anumberofmedicationscanimpairthe
absorptionorutilizationofB12.VitaminB12appearstobeacofactorinvolvedinthe
productionofnitricoxide[293],whichwouldhaveimportantimplicationsforvascular
andimmunehealth.
About50%ofdietaryB12isnormallyabsorbedviailealreceptors,mediatedbythe
intrinsicfactor,aglycoproteinfromthestomach.Theilealreceptorsbecomesaturated
with1.5to2μgofB12,limitingfurtherabsorption[216].Wheningestinglargedosesof
supplementalB12,about1%ofthedoseisabsorbedbypassivediffusionacrossthe
intestinaltract[216].Dailyneedscanbeadequatelymetinnon‐pregnant,non‐lactating
peoplebyconsuminga500μgB12supplementatleastthreetimesaweek.VitaminB12
iswellabsorbedfromeithersub‐lingualorchewabletablets.Whilethemethylcobalamin
supplementistoutedasthemoreeffectiveformofB12,itsbioavailabilityisnotsuperior
tothatofcyanocobalamin,whichisthemorestableandmostcommonlyusedformofB12
infortifiedfoodsandmanysupplements[294,295].
AdeficiencyofvitaminB12maytakeyearstodevelopinadults,asmostoftheB12
secretedintothegutviathebilegetsreabsorbed,thusconservingthebodystores[216].
Therefore,aregularconsumptionofadequateB12isimportanttoavoidasub‐clinical
deficiencythatcangoundetectedforyears.Anelevatedserummethylmalonicacid
(MMA)levelisareliableindicatorofB12deficiency[216],whiletheserumB12levelisan
insensitiveindicatorofB12status.WhileserumB12levelsbetween148and221pmol/L
(200‐300pg/mL)areconsideredborderlineB12deficiency[296],someindividualswith
B12valuesinthisrangemanifestneuropsychiatricproblemsandmemoryloss[297].Asa
goodpreventativemeasure,allvegansshouldannuallychecktheirB12status.
9.6.VitaminD
VitaminDfacilitatescalciumabsorptionfromthegut,regulatesbonemineralization,
cellgrowth,anddifferentiation.Itsotherrolesincludereductionofinflammationand
modulationofneuromuscularandimmunefunction[298].Becausecutaneousproduction
ofvitaminDfromsunlightexposureisnotadequate(especiallyintheelderly,dark‐
skinnedindividuals,andheavysunscreenusers)tomeetnutritionneedsinpopulations
livinginhighlatitudes,especiallyduringthewintermonths,regularfoodand
supplementsourcesarenecessary.FoodscontainlimitedamountsofvitaminD,so
supplementsareoftenneededtomeetneeds.Dependinguponone’sage,geographical
location,dietarypreferences,andbodyweight,adailysupplementaldoseof10–50μg

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(400to2000IU)ofvitaminDmaybeneededtoachieveoptimalserumlevelsof25‐
hydroxyvitaminD(25(OH)D)year‐round[299].
Onestudyfoundno