JournalofPediatricGastroenterologyandNutrition

41:S12–S18ÓNovember2005ESPGHAN.Reprintedwithpermission.

3.AminoAcids

METHODSLiteratureSearch

Timeframe:Publicationsearchis1992–2004plusrelevantpublicationsbefore1992.

Typeofpublications:Casecontrolandcohortstudies,randomisedcontrolledstudiesandsystematicreviews.Language:English.

KeyWords:Adolescents,children,neonates,preterminfants,parenteralnutrition,aminoacids,requirements,toxicity,de ciency.

adevelopmentaldelayinspeci cenzymesinvolvedinaminoacidsynthesishavebeendemonstrated(7–11).Theessential,non-essentialandconditionallyessen-tialaminoacidsarelistedintable1.Althougheverybodyagreesontheconceptthatsomenone-essentialaminoacidsareessentialundercertaincircumstances,somedebateexistsabouttheconditionalessentialityofarginineandproline.

METHODSFORESTIMATINGTOTALAND

INDIVIDUALAMINOACIDNEEDS

Aminoacidrequirementsaremainlydeterminedbytherateofnetproteinsynthesis,whichdependsontheavailabilityofratelimitingaminoacids.Thereareseveralphysiologicalandbiochemicalwaystodeterminewhethertheaminoacidintakeissuf cientorinexcessoftheneedsofchildren.Differentmea-surementsinassessingadequacyofaminoacidintakeincludeanthropometry(weightandlength),nitrogenbalance,metabolicindices(e.g.aminoacidconcentrations,albumin,pre-albumin,totalproteinconcentrations,bloodureanitrogen,metabolicacidosis),whole-bodynitrogenkinetics,speci caminoacidkineticsandtheindicatoraminoacidmethod.Theintakeofeachessentialaminoacidrequiredtomaintainnitrogenequi-libriuminchildrenandinfantshasbeende nedastheamountnecessarytoobtaingrowthandnitrogenbalance.

Inveterinarymedicinethefreeaminoacidconcentrationswereusedtodetectde cienciesandexcessesofdietaryaminoacids.Thisprincipleworksmorerapidlythanweightgainorgrowthstudies(12–15).Mostcurrentaminoacidsolutionsaredevelopedinasimilarfashion(16–18).

Theaminoacidindicatormethodseemstobeanaccurateandfastwaytodeterminespeci caminoacidrequirements.Ithasrecentlybeendevelopedtomeasurespeci caminoacidre-quirements(19–21)andhasbeenvalidatedinanimalmodelsofinfancy(22–24).Thetechniqueisbasedonthepartitioningofessentialaminoacidout owundersteadystateconditionsbe-tweenoxidationandproteinsynthesis.Whenasingleessentialaminoacidisde cientinthediet,theamountofproteinthatcanbesynthesizedislimited.Sincethelimitingaminoacidalsolimitstheuseofallotherdietaryaminoacidsforproteinsynthesis,thebodymustoxidizeexcessamountsoftheseaminoacids.Ifoneincreasesthedietaryamountofthelimitingaminoacid,proteinsynthesiswillincreaseandsowilltheutilizationoftheotherdietaryaminoacidswhichinturnreducestheiroxidation.Oncetherequirementforthelimitingaminoacidisreached,furtherincreasesinitsdietaryintakewillcausenofurtherincreaseinproteinsynthesis,nordecreaseintheoxida-tionoftheotheressentialaminoacids.

Theindicatoraminoacidoxidationmethodusesthisrelationship(19).Subjectsaregivenaseriesofdietscontainingvaryingamountsoftheaminoacidforwhichtherequirementistobedetermined.Theamountsvarybelowandaboverequirement.Allotheraminoacidsarefurnishedatconstant

Patients

Allchildrenwithagerangefrompretermtoadolescentwereconsideredintheseguidelines.

Outcome

Recommendationsweredevelopedfromastandpointofnutrientadequacy.Dependingonagegroups,nutrientadequacywasbasedonintrauterineaccretionrate,organdevelopment,factorialestimatesofrequirementsandaminoacidinteractions.Individualaminoacidsarediscussed.

Minimalintakesofspeci caminoacidsarethosethatmeetthespeci crequirementofchildreninthatagegroup.Maximalintakesarerecommendedtopreventexcessiveandpotentiallyharmfulintakesofaminoacids.

AMINOACIDSIntroduction

Proteinsarethemajorstructuralandfunctionalcom-ponentsofallcellsinthebody.Theyconsistofchainsofaminoacidsubunitsjoinedtogetherbypeptidebonds.Thechainlengthrangesfromtwoaminoacidstothou-sands,withmolecularweightssubsequentlyrangingfromhundredstohundredsofthousandsofDaltons.Fromanutritionalperspective,animportantaspectofaproteinisitsaminoacidcomposition.

Someaminoacidsareclassi edasessential(indis-pensable).Thoseareaminoacidsthatcannotbesyn-thesizedbyhumansandhencemustbeprovidedinthedietorparenteralsolution.Non-essentialaminoacidscanbesynthesizedfromotheraminoacidsorfromotherprecursors.Someaminoacidsarecategorizedassemi-essential.Theseaminoacidscanbesynthesizedfromotheraminoacidsbuttheirsynthesisislimitedundercertaincircumstances(1–6).Theseaminoacidsmaybeofparticularimportanceforthepreterminfantinwhom

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