Genetically Modified FoodsWord格式.docx
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Genetically Modified FoodsWord格式.docx
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Geneticallymodified(GM)cropsandfoodarebeinggrownandconsumedbythepublic,eventhough:
∙thereislittlescientificstudyabouttheirhealthrisks
∙safetytesttechnologyisinadequatetoassesspotentialharm
∙theycancarryunpredictabletoxins
∙theymayincreasetheriskofallergenicreactions
June2001
Scarcityofsafetytests
Soybeansweregeneticallyengineeredtomakethemherbicideresistant.Photo:
ScottBauer.
Howcanthepublicmakeinformeddecisionsaboutgeneticallymodified(GM)foodswhenthereissolittleinformationaboutitssafety?
Thelackofdataisduetoanumberofreasons,including:
Informationisscarceabouthealthhazards,suchastoxicityingeneticallymodified(GM)crops.
∙It’smoredifficulttoevaluatethesafetyofcrop-derivedfoodsthanindividualchemical,drug,orfoodadditives.Cropfoodsaremorecomplexandtheircompositionvariesaccordingtodifferencesingrowthandagronomicconditions.
∙PublicationsonGMfoodtoxicityarescarce.Anarticlein
Sciencemagazinesaiditall:
“HealthRisksofGeneticallyModifiedFoods:
ManyOpinionsbutFewData”.1
Infact,nopeer-reviewedpublicationsofclinicalstudiesonthehumanhealtheffectsofGMfoodexist.Evenanimalstudiesarefewandfarbetween.
∙ThepreferredapproachoftheindustryhasbeentousecompositionalcomparisonsbetweenGMandnon-GMcrops.Whentheyarenotsignificantlydifferentthetwoareregardedas“substantiallyequivalent”,andthereforetheGMfoodcropisregardedassafeasitsconventionalcounterpart.ThisensuresthatGMcropscanbepatentedwithoutanimaltesting.However,substantialequivalenceisanunscientificconceptthathasneverbeenproperlydefinedandtherearenolegallybindingrulesonhowtoestablishit.2
GMfoodsmaycausebacteriatobecomeresistanttoantibiotics.
Theycanalsoproduceallergies.
Whenfood-cropsaregeneticallymodified,(“geneticallymodified”foodisamisnomer!
)oneormoregenesareincorporatedintothecrop’sgenomeusingavectorcontainingseveralothergenes,includingasaminimum,viralpromoters,transcriptionterminators,antibioticresistancemarkergenesandreportergenes.DataonthesafetyofthesearescarceeventhoughtheycanaffectthesafetyoftheGMcrop.Forexample:
∙DNAdoesnotalwaysfullybreakdowninthealimentarytract.3,4
GutbacteriacantakeupgenesandGMplasmids5andthisopensupthepossibilityofthespreadofantibioticresistance.
∙Insertionofgenesintothegenomecanalsoresultinunintendedeffects,whichneedtobereduced/eliminatedbyselection,sincesomeofthewaystheinsertedgenesexpressthemselvesinthehostorthewaytheyaffectthefunctioningofthecrop’sowngenesareunpredictable.Thismayleadtothedevelopmentofunknowntoxic/allergeniccomponents,whichwecannotanalyzeforandseriouslylimitingtheselectioncriteria.
Currenttestingmethodsneedradicalimprovements.
Currently,toxicityinfoodistestedbychemicalanalysisofmacro/micronutrientsandknowntoxins.Torelysolelyonthismethodisatbestinadequateand,atworst,dangerous.Betterdiagnosticmethodsareneeded,suchasmRNAfingerprinting,proteomicsandsecondarymetaboliteprofiling.6
However,consumingevenminorconstituentswithhighbiologicalactivitymayhavemajoreffectsonthegutandbody’smetabolism,whichcanonlyberevealedfromanimalstudies.Thusnoveltoxicological/nutritionalmethodsareurgentlyneededtoscreenforharmfulconsequencesonhuman/animalhealthandtopinpointthesebeforeallowingaGMcropintothefoodchain.7
SafetytestsoncommercialGMcrops
GMtomatoes:
ThefirstandonlysafetyevaluationofaGMcrop,theFLAVRSAVRTM
tomato,wascommissionedbyCalgene,asrequiredbytheFDA.ThisGMtomatowasproducedbyinsertingkanrgenesintoatomatobyan‘antisense’GMmethod.Thetesthasnotbeenpeer-reviewedorpublishedbutisontheinternet.8
Theresultsclaimtherewerenosignificantalterationsintotalprotein,vitaminsandmineralcontentsandintoxicglycoalkaloids.9
Therefore,theGMandparenttomatoesweredeemedtobe“substantiallyequivalent.”
Inacutetoxicitystudieswithmale/femalerats,whichweretube-fedhomogenizedGMtomatoes,toxiceffectswereclaimedtobeabsent.Inaddition,itwasconcludedthatmeanbodyandorganweights,weightgains,foodconsumptionandclinicalchemistryorbloodparameterswerenotsignificantlydifferentbetweenGM-fedandcontrolgroups.However:
SomeratsdiedwithinafewweeksaftereatingGMtomatoes.
∙Theunacceptablywiderangeofratstartingweights(±
18%to±
23%)invalidatedthesefindings.
∙Nohistologyontheintestineswasdoneeventhoughstomachsectionsshowedmild/moderateerosive/necroticlesionsinuptosevenoutoftwentyfemaleratsbutnoneinthecontrols.However,thesewereconsideredtobeofnoimportance,althoughinhumanstheycouldleadtolife-endangeringhemorrhage,particularlyintheelderlywhouseaspirintopreventthrombosis.
∙SevenoutoffortyratsonGMtomatoesdiedwithintwoweeksforunstatedreasons.
∙ThesestudieswerepoorlydesignedandthereforetheconclusionthatFLAVRSAVRTM
tomatoesweresafedoesnotrestongoodscience,questioningthevalidityoftheFDA’sdecisionthatnotoxicologicaltestingofotherGMfoodswillinfutureberequired.
GMmaize:
TwolinesofChardonLLherbicide-resistantGMmaizeexpressingthegeneofPhosphinothricinAcetyltransferaseEnzyme(PAT-PROTEIN)beforeandafterensilingshowedsignificantdifferencesinfatandcarbohydratecontentscomparedwithnon-GMmaizeandwerethereforesubstantiallydifferent.ToxicitytestswereonlyperformedwiththePAT-PROTEINeventhoughwiththistheunpredictableeffectsofthegenetransferorthevectororgeneinsertioncouldnotbedemonstratedorexcluded.Thedesignoftheseexperimentswasalsoflawedbecause:
Rats’abilitytodigestwasdecreasedaftereatingGMcorn.
∙Thestartingweightoftheratsvariedbymorethan±
20%andindividualfeedintakeswerenotmonitored.
∙FeedconversionefficiencyonPAT-PROTEINwassignificantlyreduced.
∙Urineoutputincreasedandseveralclinicalparameterswerealsodifferent.
∙Theweightandhistologyofthedigestivetract(andpancreas)wasnotmeasured.
Thus,GMmaizeexpressingPAT-PROTEINmaypresentunacceptablehealthrisks.
Compositionalstudies
Allergencontentincreasedwhensoybeansweregeneticallymodified.
GMsoybeans:
Tomakesoybeansherbicideresistant,thegeneof5-enolpyruvylshikimate-3-phosphatesynthasefrom
Agrobacterium
wasused.SafetytestsclaimtheGMvarietytobe“substantiallyequivalent”toconventionalsoybeans.10
ThesamewasclaimedforGTS(glyphosate-resistantsoybeans)sprayedwiththisherbicide.11
However,severalsignificantdifferencesbetweentheGMandcontrollineswererecorded10
andthestatisticalmethodusedwasflawedbecause:
∙InsteadofcomparingtheamountsofcomponentsinalargenumberofsamplesofeachindividualGTSwithitsappropriateparentlinegrownside-by-sideandharvestedatthesametime,theauthorscomparedsamplesfromdifferentlocationsandharvesttimes.
∙Therewerealsodifferencesinthecontentsofnaturalisoflavones(genistein,etc.)withpotentialimportanceforhealth.12
∙Additionally,thetrypsininhibitor(amajorallergen)contentwassignificantlyincreasedinGTS.10
Becauseofthis,andthelargevariability(±
10%ormore),thelinescouldnotberegardedas“substantiallyequivalent.”
GMpotatoes:
Thereisonlyonepeer-reviewedpublicationonGMpotatoesthatexpressthesoybeanglyciningene.13
However,theexpressionlevelwasverylowandnoimprovementsintheproteincontentoraminoacidprofilewereobtained.
GMrice:
Thekindthatexpressessoybeanglyciningene(40-50mgglycinin/gprotein)hasbeendeveloped14
andisclaimedtocontain20%moreprotein.However,theincreasedproteincontentwasprobablyduetoadecreaseinmoistureratherthantrueincreaseinproteinputtingaquestionmarkoverthesignificanceofthisGMcrop.
ThetoxinlevelofGMcottonisunpredictable.
GMcotton:
SeverallinesofGMcottonplantshavebeendevelopedusingagenefrom
Bacillusthuringiensis
subsp.
kurstaki
providingincreasedprotectionagainstmajorlepidopteranpests.Thelineswereclaimedtobe“substantiallyequivalent”toparentlines15
inlevelsofmacronutrientsandgossypol,cyclopropenoidfattyacidsandaflatoxinlevelswerelessthanthoseinconventionalseeds.However,becauseoftheuseofinappropriatestatisticsitisquestionablewhethertheGMandnon-GMlinesweretrulyequivalent,particularlyasenvironmentalstressescouldhaveunpredictableeffectsonantinutrient/toxinlevels.16
Nutritional/toxicologicalstudies
Herbicide-resistantsoybean:
Studieshavebeenconductedonthefeedingvalue17
andpossibletoxicity18
forrats,broilerchickens,catfishanddairycowsoftwoGMlinesofglyphosate-resistantsoybean(GTS).Thegrowth,feedconversionefficiency,catfishfilletcomposition,broilerbreastmuscleandfatpadweightsandmilkproduction,rumenfermentationanddigestibilitiesincowswereclaimedtobesimilarforGTSandnon-GTS.However:
∙TheseexperimentswerepoorlydesignedsincethehighdietaryproteinconcentrationandthelowinclusionlevelofGTScouldhavemaskedanyGMeffect.
∙Noindividualfeedintakes,bodyororganweightsweregivenandnohistologywasperformed,exceptsomequalitativemicroscopyonthepancreas.
∙ThefeedingvalueofthetwoGTSlineswasnotsubstantiallyequivalenteitherbecausetheratsgre
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