UNit6儿童营养 Nutritional requirements ofchildern.docx

UNit6儿童营养 Nutritional requirements ofchildern.docx

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UNit6儿童营养Nutritionalrequirementsofchildern

Unit4

Nutrition,healthandschoolchildren

Overthelast50years,therehasbeenachangeinthepredominantconcernsaboutthedietsandhealthofschoolagedchildren.Historically,thefocushasbeenontheprovisionofsufficientnutrientsandenergyinrelationtocurrentandfutureneeds,butprovidingdietarybalanceandencouraginglesssedentarylifestylesarenowviewedasthemainpriorities.Personal,SocialandHealthEducationprogrammesofstudy,togetherwithothergovernmentinitiativessuchastheWiredforHealthwebsite,theSchoolFruitSchemewillcontributetowardsempoweringchildrenwithknowledgeandopportunitiestomakeinformedchoicesfortheirfuturehealth.

TextA

Nutritionalrequirementsofchildren

Dietaryreferencevalues

Ithaslongbeenrecognizedthatgoodnutritionisofcrucialimportanceforthewell-being,growthanddevelopmentofchildren.Eventhoughtheenergycostofgrowthisaminorcomponentoftotalenergyrequirements,growthrateisasensitiveindicatorofoveralldietaryadequacy.Inthelongerterm,foodpatternsinchildhood,particularlyadolescence,cansetthesceneforfuturedietarypreferencesandeatingbehaviorinadultlife.Thereisalsosubstantialevidencethatpoordietandpoorphysicalactivitypatternsinchildhoodcanstoreupproblemsthatmanifestlaterinlife,particularlyinrelationtoheartdisease,obesity,type2diabetesandsomeformsofcancer.

Thenutritionalrequirementsofchildrenarehighinrelationtotheirsizebecauseofthedemandsforgrowth,inadditiontorequirementsformaintenanceandphysicalactivity.Earlypubertywillalsoaffectnutritionalrequirements.

Tables1and2showtheUKDietaryReferenceValues（DRV）forenergyandselectednutrientsforchildrenfrom4to18years.Theseareusedasaguidetotheadequacyofchildren’sdiets.Theestimatesofrequirementsforprotein,vitaminsandmineralsforgroupsofchildrenareexpressedasReferenceNutrientIntakes（RNI）,theRNIbeingtheamountthatissufficientforalmostall（97.5%）individuals.TheEstimatedAverageRequirement（EAR）isusedasanindicationofenergyrequirements,andbydefinition50%ofpeopleinadefinedgroupwillneedlessthanthistomaintainenergybalanceand50%willneedmore.TheenergyEARassumesasedentarylifestyle（asthisisthesituationforthemajorityofpeopleinBritain,thoughincreasedactivityisadvised）;useoftheRNI（equivalenttothemeanplus2standarddeviations）wouldmeanthatpredictedintakeswouldbegreaterthanmostpeople’sneedsandhencewouldresultinweightgainoveraperiodoftime.Becauseofinsufficientdata,atthetimetheDRVswereset,fromUKstudiesmeasuringactualenergyexpenditureinchildrenaged4–10years,theestimatedaveragerequirementsforenergybydifferentageandgendergroupshavebeenbasedonintakedatafromanumberofstudiesconductedinhealthywell-nourishedchildrenintheUKandelsewhereTheenergyrequirementsforolderchildren11–18years,however,arebasedonenergyexpendituredata,expressedasmultiplesofbasalmetabolicrate.

Table1DietaryReferenceValuesforboysaged4–18years

Age（years）Units4–67–1011–1415–18

EnergyMJ7.168.249.2711.51

Kcal1715197022002755

Proteing19.728.342.155.2

Ironmg6.18.711.311.3

Calciummg45055010001000

Zincmg6.57.09.09.5

Magnesiummg120200280300

Phosphorusmg350450775775

Sodiummg700120016001600

VitaminAmg500500600700

VitaminB1,thiaminmg0.70.70.91.1

VitaminB2,riboflavinmg0.81.01.21.3

Niacinmg11121518

VitaminB6mg0.91.01.21.5

VitaminB12mg0.81.01.21.5

Folatemg100150200200

VitaminCmg30303540

Recommendationsforthepopulationingeneral,i.e.allages

Fat%foodenergy35

ofwhichsaturates%foodenergy11

Carbohydrate%foodenergy50

ofwhichstarch,intrinsicsugarsandmilksugars

%foodenergy39

ofwhichNMEsugars*%foodenergy11

Source:

DepartmentofHealth1991.*Non-milkextrinsicsugars.

Table2DietaryReferenceValuesforgirlsaged4–18years

Age（years）Units4–67–1011–1415–18

EnergyMJ6.467.287.928.83

Kcal1545194018452110

Proteing19.728.341.245.0

Ironmg6.18.714.814.8

Calciummg450550800800

Zincmg6.57.09.07.0

Magnesiummg120200280300

Phosphorousmg350450625625

Sodiummg700120016001600

VitaminAmg500500600600

VitaminB1,thiaminmg0.70.70.70.8

VitaminB2,riboflavinmg0.81.01.11.1

Niacinmg11121214

VitaminB6mg0.91.01.01.2

VitaminB12mg0.81.01.21.5

Folatemg100150200200

VitaminCmg30303540

Recommendationsforthepopulationingeneral,i.e.allages

Fat%foodenergy35

ofwhichsaturates%foodenergy11

Carbohydrate%foodenergy50

ofwhichstarch,intrinsicsugarsandmilksugars

%foodenergy39

ofwhichNMEsugars*%foodenergy11

Source:

DepartmentofHealth1991.*Non-milkextrinsicsugars.

Sincethe1985FAO/WHO/UNU（FoodandAgricultureOrganization/WorldHealthOrganization/UnitedNationalUniversity）report,morehasbeenlearntabouttheenergyexpenditureofchildrenandadolescents,andthedistributionoftimespentinactivitiesofdifferinglevelsofenergyexpenditure,largelyasaresultoftheapplicationofthedoublylabeledwatermethodandothertechniquessuchasheartratemonitoring（Torunetal.1996）.Torunetal.havereviewedtheavailabledataandpublishedrecommendationsforresearchpriorities,designedtohelpprovideamorecompletepictureofchildren’senergyneeds.Theyhighlighttheimportanceofcouplingdietaryenergyguidelineswithstrongrecommendationsonphysicalactivity,notingthattheminimumamountofactivitycompatiblewithgoodhealthinchildhoodhasnotbeenpreciselydetermined.AreviewofenergyrequirementsiscurrentlybeingundertakenbyFAOandothers.

Desirableintakesofcarbohydratesandfatsareexpressedasaproportionoftotaldietaryenergy.ThesetakeintoaccounteatinghabitsintheUKandthepracticalimplicationsofachievingchangeinlinewithwhatisconsidereddesirableforhealth.Theyhavebeencalculatedwiththeneedsoftheadultpopulationinmind.Whilstthesevaluesprovideausefulguideforolder（schoolage）children,theyshouldnotbeappliedrigorouslytothedietsofpre-schoolchildren.

Therearenospecificestimatesforthedesirableamountoffibre（non-starchpolysaccharide,[NSP]）forchildren.TheDepartmentofHealth（1991）recommendsthatchildrenshouldhaveproportionallylowerfibreintakesthanadults;theDRVforadultsis18gofNSPperday.ItshouldbenotedthatrecentlytheFoodStandardsAgencyhasannouncedthatdifferentmethodology（theAmericanAssociationofAnalyticalChemists（AOAC）methodratherthantheEnglystmethod）istobeusedtoassessthedietaryfibrecontentoffoods;thischangewillnecessitatereassessmentoftheDRVfigureasthetwomethodsarenotcomparable.

Formostessentialnutrients,requirementshavebeenestimatedbyextrapolatingfrompublisheddataforinfantsandadults,aslittlespecificinformationforschoolagedchildrenexists.Duringadolescence,nutrientrequirementsaresethigherforboysthanforgirlsbecauseoftheirincreasedratesofgrowth,bonesynthesisandbonemineralisation.Oncemenarcheisreachedandperiodsstart,girlsloseonaveragetheequivalentof12.5mmol（1mmol=55.9mg）ofironperday,althoughthereiswidevariationintheamountofbloodlost,withgirlsonthe95thcantlelosingaround34mmolperday.Thesedatahavebeenusedtosettheironrequirementsforgirlsatalevelhigherthanforboysandmuchhigherthanduringtheprepubertalperiod.

Similarly,therearenoestimatedrequirementsforvitaminDbecauseitisexpectedthat,withtheexceptionofveryyoungandveryelderlypeople,mostpeopleobtainanadequateamountofthevitaminviatheactionofsunlightontheskin.However,ithasbecomeapparentthatasubstantialproportionofchildrenhavelowvitaminDstatusandthismaycarrypublichealthimplications.Thereislittleevidencetosuggestdifferentrequirementsamongethnicgroups,althoughtheDepartmentofHealth（1980）continuestorecommendthatallAsianchildrentakevitaminDsupplementsasaprecaution,particularlywherereligionandcustomsdictatethattheirskiniskeptcoveredoutside,resultinginareducedexposureoftheirdarkerskintotherelativelyweaksunlightavailableintheUK.

Fluidrequirements

Fluidrequirementsareanoftenoverlookedaspectofdiet.Toreplacefluidlosses,whichoccurviaurine,sweatandbreath,1.5mLperkcalexpendedhasbeenrecommendedasatotalfluidrequirement.Thisamountstoatotalfluidintakeofapproximately2600mLperdayfora7-year-oldgirland4000mLperdayfora15-year-oldboy.However,allowancesneedtobemadeforthefluidcontentoffoodsincludedinthediet.Itisnowgenerallyacceptedthat6–8glassesoffluidperday（appropriateforthesizeandageofthechild）shouldbesufficient,althoughmorewillbeneededinhotweatherandaftervigorousphysicalactivity.Inadults,thirstisagoodindicatoroffluidneeds,ifrespondedtopromptly.However,childrenmayneedtobeencouragedtodrinksufficienttorehydrate,e.g.afterexercise,andprovisionofflavoredwaterisoftenmoreacceptable.Iflostfluidisnotreplaced,dehydrationwillresult.Intheshortterm,poorhydrationcausesheadaches,continenceproblemsandconstipation,butinthelongertermcanleadtourinarytractinfections,kidneystonesandkidneydisease.Thereisalsoanecdotalevidencethatalertnessandcognitiveperformancecanbecompromisedby