Essential fatty acids: definition, functions, foods - Tuscany ...

Essential fatty acids or EFAs are fatty acids, a class of lipids, that cannot be synthesized by animals, and, like other essential nutrients ... EssentialfattyacidsorEFAsarefattyacids,aclassoflipids,thatcannotbesynthesized byanimals,and,likeotheressentialnutrients,mustbeobtainedfromthediet.Theyarelinoleicacid orLAor18:2n-6,andalpha-linolenicacid orALAor18:3n-3. Animalscannotsynthesizethesetwofattyacidsduetothelackofdelta-12desaturase(E.C.1.14.19.6)anddelta-15desaturase(EC1.14.19.25).Theseenzymesintroducecisdoublebondsbeyondcarbon9,andarepresentinplantsandmicroorganisms,suchassomebacteria,fungiandmolds.Inparticular,inplants: delta-12desaturase,presentintheplastids,catalyzesthesynthesisoflinoleicacidfromoleicacid,byintroducingadoublebondatdelta-12position,namely,betweencarbons6and7fromthemethylendofthefattyacid; delta-15desaturase,presentintheplastidsandintheendoplasmicreticulumofphytoplanktonandvascularterrestrialplants,catalyzesthesynthesisofalpha-linolenicacidfromlinoleicacidbyintroducingadoublebondatdelta-15position,namely,betweencarbons3and4fromthemethylendofthefattyacid. SynthesisofEFAs Linoleicacidandalpha-linolenicacidaretheprecursorstoomega-6polyunsaturatedfattyacidsandomega-3polyunsaturatedfattyacids.Indeed,animalscansynthesize,althoughwithvariableefficiency,theotheromega-3andomega-6polyunsaturatedfattyacids,lipidswith20,22,or24carbonatoms,andupto6doublebonds,suchasarachidonicacid orARAor20:4n6anddocosahexaenoicacid orDHAor22:6n3,duetothepresenceofdesaturasesthatintroducedoublebondsatdelta-5anddelta-6positionsandelongasesthatcatalyze theelongationofthecarbonchain. Intheabsenceofdietaryessentialfattyacids,aratherrarecondition,theotheromega-3andomega-6fattyacidsbecomeessential,too.Forthisreason,theyaredefinedbysomeasconditionallyessentialfattyacids. Itshouldbepointedoutthatallessentialfattyacidsarepolyunsaturatedmolecules,butnotallpolyunsaturatedfattyacidsareessential,suchasthosebelongingtotheomega-7andomega-9families. CONTENTS Discoveryofessentialfattyacids FunctionsofEFAsandtheirPUFAderivatives Foodsrichinessentialfattyacids References Discoveryofessentialfattyacids The firstevidenceoftheirexistencedatesbackto1918,whenHansAronsuggestedthatdietaryfatcouldbe essential forthehealthygrowthofanimalsandthat,inadditiontotheircaloriccontribution,therewasainherentnutritivevalueduetothepresenceofcertain lipid molecules. In1927,HerbertM.EvansandGeorgeOswaldBurrdemonstratedthat,despitetheadditionofvitaminsA,D,andEtothediet,adeficiencyoffatseverelyaffectedbothgrowthandreproductionofexperimentalanimals.Therefore,theysuggestedthepresenceofanessentialsubstanceinthefatthattheycalledvitaminF. ElevenyearsafterAronwork,in1929,GeorgeBurrandhiswifeMildredLawsonhypothesizedthatwarm-bloodedanimalswerenotabletosynthesizeappreciableamountsofcertainfattyacids.Oneyearlater,theydiscoveredthatlinoleicacidwasessentialforanimals,anditwastheywhocoinedthetermessentialfattyacid. However,EFAdeficiencyinhumanswasfirstdescribedbyArildHansenetal.onlyin1958,ininfantsfedamilk-basedformulalackingthem. Andin1964,thankstotheresearchofVanDorpetal.andBergstroemetal.,oneoftheirbiologicalfunctionswasdiscovered:beingtheprecursorsforthesynthesisofprostaglandins. FunctionsofEFAsandtheirPUFAderivatives EFAsandtheirpolyunsaturatedfattyacidderivativesplayimportantbiologicalfunctions. Theyarestructuralcomponentsofcellularmembranes,modulating,forexample,theirfluidity,particularlyDHA. Theyareessentialforthedevelopmentandfunctioningofthe nervoussystem,particularlyARAandDHA. Theyareinvolvedinsignaltransduction,particularlyomega-6polyunsaturatedfattyacids,suchasARA. Theyareinvolvedintheregulationofgenesencodinglipolyticandlipogenicenzymes,beingstronginducersoffattyacidoxidation,aswellasinhibitorsoftheirsynthesisandthatoftriglycerides,atleastinanimalmodels. Theyact,forexample,as: activatorsoftheperoxisomeproliferator-activatedreceptorα(PPAR-α)thatstimulatesthetranscriptionofgenesencodinglipolyticenzymesaswellasmitochondrialandperoxisomalbeta-oxidationenzymes,andinhibitorsoftranscriptionofgenesencodingenzymesinvolvedinlipogenesis; inhibitorsofsterolresponsiveelementbindingprotein-1c(SREBP-1c)genetranscription,atranscriptionfactorrequiredforliverfattyacidandtriglyceridesynthesisinducedbyinsulin. Note:PUFAsalsoincreaseSREBP-1cmRNAdegradationaswellasSREBP-1degradation. Theyareprecursorsforsignalingmolecules,withautocrineandparacrineaction,thatactasmediatorsinmanycellularprocesses,suchaseicosanoids. Theyareessentialintheskin,especiallylinoleicacidinsphingolipidsofthestratumcorneum,wheretheycontributetotheformationofthebarrieragainstwaterloss. Theyhaveacrucialroleinthepreventionofmanydiseases,particularlycoronaryheartdisease,actingasantihypertensive,antithrombotic,andtriglyceride-loweringagents. Noteworthy,theirenergystoragefunctionisquantitativelyunimportant. Foodsrichinessentialfattyacids Linoleicacidisthemostabundantpolyunsaturatedfattyacid intheWesterndiet,andaccountsfor85-90%ofdietaryomega-6polyunsaturatedfattyacids. Therichestdietarysourcesarevegetableoilsandseedsofmanyplants,suchas: saffloweroil,~740mg/g; sunfloweroil,~600mg/g; soybeanoil,~530mg/g; cornoil,~500mg/g; cottonseedoil,~480mg/g; walnuts,~340mg/g; brazilnuts,~250mg/g; peanutoil,~240mg/100g; rapeseedoil,~190mg/g; peanuts,~140mg/g; flaxseedoil,~135mg/g. Linoleicacidispresentinfairamountsalsoinanimalproductssuchaschickeneggsorlard,becauseitispresentintheirfeed. Itshouldbenotedthatsomeofthemajorsourcesoflinoleicacid,suchaswalnuts,flaxseedoil,soybeanoil,andrapeseedoilarealsohighinalpha-linolenicacid. Someoftherichestdietarysourcesofalpha-linolenicacidare: flaxseedoil,~550mg/g rapeseedoil,~85mg/g soybeanoil,~75mg/g OtherfoodsrichinALAincludenuts,~70mg/g,andsoybeans,~10mg/g. References AkohC.C.andMinD.B.“Foodlipids:chemistry,nutrition,andbiotechnology”3thed.2008 BergstroemS.,DanielssonH.,KlenbergD.andSamuelssonB.Theenzymaticconversionofessentialfattyacidsintoprostaglandins.JBiolChem1964;239:PC4006-PC4008 BurrG.andBurrM.Anewdeficiencydiseaseproducedbytherigidexclusionoffatfromthediet.JBiolChem1929;82:345-367 ChowChingK.“Fattyacidsinfoodsandtheirhealthimplication”3thed.2008 EvansH.M.andG.O.Burr.Anewdietarydeficiencywithhighlypurifieddiets.III.Thebeneficialeffectoffatinthediet.ProcSocExpBiolMed1928;25:390-397.doi:10.3181/00379727-25-3867 SmithW.,MukhopadhyayR.Essentialfattyacids:theworkofGeorgeandMildredBurr.JBiolChem2012;287(42):35439-35441.doi:10.1074/jbc.O112.000005 VanDorp.D.A.,BeerthuisR.K.,NugterenD.H.andVonkemanH.Enzymaticconversionofall-cis-polyunsaturatedfattyacidsintoprostaglandins.Nature1964;203:839-841.doi:10.1038/203839a0 Postnavigation PreviousPostNutritionforathletes:strategiesfortrainingandcompetitionNextPostOmega-3fattyacids:synthesis,mechanismofaction,healthbenefits,andfoods RecentPosts Fischer-Rosanoffconvention Fischerprojections Energyyieldofglycogenunderaerobicandanaerobicconditions RSsystem:thepriorityrules Chiralityinorganicchemistry Biochemistry,metabolismandnutrition Categories Biochemistry Nutrition Organicchemistry Phytochemicals Utilizziamoicookieperesseresicurichetupossaaverelamiglioreesperienzasulnostrosito.Secontinuiadutilizzarequestositonoiassumiamochetunesiafelice.OkPrivacypolicy