CorrespondenceKarenHofmanwitsaczaPRICELESSSAPriorityCostEffectiveLessonsinSystemStrengtheningSouthAfricaJohannesburgSouthAfricaWitsMedicalResearchCouncilRuralHealthandHealthTransitionsUnit ID: 187669
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RESEARCHARTICLEOpenAccess Evidencethatataxonsugarsweetened beveragesreducestheobesityrate:a meta-analysis MariaACabreraEscobar 1 ,JLennertVeerman 2 ,StephenMTollman 1,3 ,MelanieYBertram 1 andKarenJHofman 1,3* Abstract Background: Excessintakeofsugarsweetenedbeverages(SSBs)hasbeenshowntoresultinweightgain.To addressthegrowingepidemicofobesity,oneoptionistocombineprogrammesthattargetindividualbehaviour increases,andtheirpotentialimpactonconsumptionlevels,obesity,overweightandbodymassindex(BMI).The possibilityofswitchingtoalternativedrinksisalsoconsidered. Methods: Thefollowingdatabaseswereused:Pubmed/Medline,TheCochraneDatabaseofSystematicReviews, GoogleScholar,Econlit,NationalBureauofEconomicsResearch(NBER),ResearchPapersinEconomics(RePEc). ArticlespublishedbetweenJanuary2000andJanuary2013,whichreportedchangesindietorBMI,overweight and/orobesityduetoataxon,orpricechangeof,SSBswereincluded. Results: Ninearticlesmetthecriteriaforthemeta-analysis.SixwerefromtheUSAandoneeachfromMexico,Brazil andFrance.Allshowednegativeown-priceelasticity,whichmeansthathigherpricesareassociatedwithalower demandforSSBs.Pooledownprice-elasticitywas 1.299(95%CI:-1.089--1.509).Fourarticlesreportedcross-price elasticities,threefromtheUSAandonefromMexico;higherpricesforSSBswereassociatedwithanincreasedde- mandforalternativebeveragessuchasfruitjuice(0.388,95%CI:0.009 0.767)andmilk(0.129,95%CI:-0.085 0.342),andareduceddemandfordietdrinks( 0.423,95%CI:-0.628--1.219).SixarticlesfromtheUSAshowedthat ahigherpricecouldalsoleadtoadecreaseinBMI,anddecreasetheprevalenceofoverweightandobesity. Conclusions: incomecountriesandidentifypotentialhealthgainsandthewiderimpactonjobs,monetarysavingstothehealth sector,implementationcostsandgovernmentrevenue.Context-specificcost-effectivenessstudieswouldallowpol- icymakerstoweighthesefactors. Keywords: Obesity,Fiscalpolicy,Tax,Non-communicablediseases(NCDs),Highincomecountries,Middleincome countries,SugarSweetenedBeverages(SSBs),Elasticity,Demand,Price Background Obesityisaglobalepidemicandisamajorriskfactor forthegrowingburdenofnon-communicablediseases (NCDs)includingheartdiseases,diabetesandsomecan- cers[1,2].Althoughpreviouslyconsideredaproblemof highincomecountries(HICs),NCDsarenowhavinga majorimpactontheeconomyoflowandmiddleincome countries(LMICs)[3].Inthepastthreedecadesthere havebeenconsiderablechangesinlifestylearoundthe world,helpedalongbyglobalisationofthefoodsupply andurbanisation[4].Thesechangesaffectdietandde- creaselevelsofphysicalactivity,therebyincreasingbody massindex(BMI)[5].TheGlobalBurdenofDisease communicablediseasesinadultsovertheperiodfrom 1990to2010,bothgloballyandineachregion[6].Dietary *Correspondence: Karen.Hofman@wits.ac.za 1 PRICELESSSA(PriorityCostEffectiveLessonsinSystemStrengtheningSouth Africa),Johannesburg,SouthAfrica 3 Wits/MedicalResearchCouncilRuralHealthandHealthTransitionsUnit, SchoolofPublicHealth,FacultyofHealthSciences,Universityof Witwatersrand,Johannesburg,SouthAfrica Fulllistofauthorinformationisavailableattheendofthearticle ©2013CabreraEscobaretal.;licenseeBioMedCentralLtd.Thisisanopenaccessarticledistributedunderthetermsofthe CreativeCommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse, distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited. CabreraEscobar etal.BMCPublicHealth 2013, 13 :1072 http://www.biomedcentral.com/1471-2458/13/1072 riskfactors(includinglowintakeoffruits,vegetables,wholegrains,nutsandseeds,andomega-3fattyacids)andphysicalinactivityareestimatedtoberesponsiblefortenpercentoftheglobalhealthloss,expressedasdisability-adjustedlifeyears[6].Middleincomecountries,inparticular,facemanychal-lengesgivenfar-reachingepidemiologicalanddemographictransitionsunderway[7,8].Forexample,SouthAfricare-portedthehighestprevalenceofpeopleclassifiedasover-weightorobese(29%ofmenand56%ofwomen)ofallcountriesinAfrica[9].DatafromtheNationalBurdenofDiseaseStudyinSouthAfricashowthatNCDswerere-sponsiblefor28%ofthediseaseburdenin2004,whichissimilarinmagnitudetotheHIV/AIDSburden[10].Worldwide,despitelifestylechangeprogrammestopre-ventobesity,thisepidemicisgrowing.Interestismountingindevelopingcombinedapproachestoaddressindividualbehaviourchangetogetherwithpopulation-orientedfiscalpoliciessuchastaxandsubsidiestoencouragehealthierfoodconsumptionpatterns.Forexample,inHungary,afattaxispartofafiscalpolicytoaddresstheobesityepi-demic[11].SeveralstatesintheUSAhavealsointroducedanexcisetaxonsugarsweetenedbeverages(SSBs),theori-ginalintentionbeingtoraiserevenue,butthisisnowcon-sideredasanti-obesitypolicy[12].WhilemanystudiestodatecomefromHICs,thereislimitedinformationinthepublishedliteratureregardinglegislativeandfiscalchangespolicyinLMICs.Variouscategoriesoffoodproductshavebeenrecom-mendedforpolicyactiontoimprovehealth.Thesein-cludeprocessedfood(highinsalt,sugarandfat),highenergydensityfood(energydensityreferstotheamountofenergyinagivenweightoffoodinkcal/gorkJ/g)[13],fastfood,foodcontainingsaturatedfat,junkfoodandsoftdrinks[14].InSouthAfrica,legislationhasnowbeenpassedtoregulatesaltinprocessedfood[15,16].Withrespecttoobesity,aneffectivestartingpointtodi-minishunhealthyfoodconsumptionmightbethroughtaxingofSSBs[17].Theapplicationofanexcisetaxontheseproductsisanattractiveoptionbecause,whileSSBsareasignificantcontributorstotheenergyintakeinmanypopulations(forexample,theyaccountforabout7%ofallcaloriesconsumedintheUS[18];whereasforUSchildrenandadolescentsthisis11%[19])theyprovidelittleornonutritionalvalue[20-23].Further,SSBsaremarketedaggressively[24]andareeasilyaccessibletoallagegroupsthroughvendingmachines,restaurants,schools,cafeteriasandshops,aswellasathome[25,26].Arecentreviewcon-cludesthatthecumulativeevidencefromobservationalstudiesandexperimentaltrialsissufficienttoconcludethatregularconsumptionofSSBscausesexcessweightgain[19].ThelinkbetweenintakeofSSBsandobesity-relatedhealthoutcomesiswellestablished[27-29],asisthelinkbetweentheintakeofSSBsandconditionssuchasosteo-porosis[30]anddentalcaries[28].FromanearlyagethisposesariskoflownutrientintakebecausechildrentendtosubstituteSSBsforhealthierdrinks[28,31].ArangeofclinicaltrialsandcohortstudiesprovideevidenceforacausalassociationbetweentheintakeofSSBsandobesity[32].ItispossiblethatasubgroupofindividualswithagreatergeneticpredispositionmaybemoresusceptibletoobesityinducedbySSBs[29].Interventionsoutsidethehealthcaresystemcanhaveasignificantimpactonanationshealth,asrecognisedinWHOhealth-in-all-policiesframework[33].Smallchangesindietformanyindividualscantranslateintolargepopulationhealthgainsatrelativelylowcost[34]andgovernmentfinancedepartmentsinparticularcanimprovepopulationhealthbyestablishingincentivesanddisincentivestodrivechangethroughoutthefoodsys-tem,includingconsumerpurchases[35].Ifgovernmentdepartmentsthatdonothavehealthastheirprimaryre-sponsibilityaretoconsiderhealth-promotinginterven-tions,evidenceontheeffectivenessofthoseoptionsisneeded[36].ThisreviewevaluatesthepublishedevidenceforSSBtaxesorpriceincreases,andtheirpotentialimpactonconsumptionlevelsandeffectsonobesity,overweightandBMI.Thepossibilityofswitchingtoalternativedrinksisalsoconsidered.Twopreviousstudieshavere-portedpooledestimatesofpriceelasticitiesinthecon-sumptionofSSBs,butbothwererestrictedtodatafromtheUS[37,38].Thepresentstudywillalsoincludenon-USstudies,andsocontributetotheevidencebaseonthecontributionthatSSBtaxationcanmaketoimprov-ingdietsandhealtharoundtheworld.Asystematicliteraturereviewwasconducted,includingoriginalresearcharticles,workingpapers,andeditorialsrelatedtoSSBs.ArticlespublishedbetweenJanuary2000andJanuary2013wereselected.ManytermsareusedtodescribeSSBs.Theseincludesoftdrinks,sugarydrinks,non-alcoholicdrinks,soda,sweetdrinks,beverage,fruitdrinks,sportdrinks,colddrinksandcarbonatedSSBs.Otherbeveragesincludingfullcreammilk,low-fatmilk,skimmilk,water,teaandcoffeewereexcluded.Thesedrinksmaycontainsomenutritionalvalueandnoneofthemcontainsugaraddedpriortopackaging,sotheirrelationshipwithobesityisnotasdirectitisforSSBs.TheinclusioncriteriawerearticlesinEnglishfromanycountry,withoriginalevidenceonthequantitativeim-pactofSSBpricechangesontheconsumptionofSSBs,consumptionofotherdrinks,orweightloss,obesityorBMI.Forthemeta-analysis,weexcludedarticlesthatdidnotreportstandarderrororconfidenceintervalontheCabreraEscobaretal.BMCPublicHealth:1072Page2of10http://www.biomedcentral.com/1471-2458/13/1072 own-priceelasticityand/orcross-priceelasticity.ArticlesthatdidnotclearlydefinethetypeofSSBswerealsoFigure1showstheliteraturesearchaccordingtothefollowingkeywordsanddatabases:Keywordssearchedwere:nutritionANDpolicyANDtaxlegislationANDobesitytaxfoodelasticityofpolicyANDsoftdrinkpolicyANDfastfoodANDpriceselasticityANDnutritionfattaxDatabasesusedwere:Pubmed/Medline,TheCochranedatabaseofsystematicreviews,GoogleScholar,EconLit(AEA),NationalBureauofEconomicsResearch(NBER),andResearchPapersinEconomics(RePEc).Thefirstauthorcarriedoutthesearch,appliedthein-clusioncriteriaandextractedthedata,infrequentcon-sultationwithasecondresearcher(JLV).WeusedanMSExcel-baseddataextractionformthatwaspilotedonasubsetofthedataandsubsequentlyrevised.Thefollowingquantitativeresultswereextracted:own-priceelasticity(percentagechangeinquantitydemandedandstandarderror),crosspriceelasticity(percentagechangeinquantitydemandedandstandarderror)(seeTable1def-initions)[39,40],orimpactonobesity(percentagepointsandstandarderror),overweight(percentagepointsandstandarderror)orBMI(kg/m2andstandarderror),duetoataxorpricechangeonSSBs.Ifthedatawaspresentedinothermetricsvalues,thiswaschangedtothemetricsvalueofinterestusingtheBMIandcross-priceelasticityformula.Ifthearticleslackedcertaindataoriftheanalyseswereun-clear,theauthorswerecontactedforadditionalinforma-tionorclarification.Meta-XL,atoolformeta-analysisinMicrosoftExcel,wasusedtosynthesizeresultsforown-andcross-price Figure1Literaturesearch.CabreraEscobaretal.BMCPublicHealth:1072Page3of10http://www.biomedcentral.com/1471-2458/13/1072 Table1DefinitionofpriceelasticityOwn-priceelasticityCross-priceelasticityToestimatetheimpactoftaxesonspecificfoods,itisimportanttoknowjusthowresponsivequantitydemandedistochangeinprice.Own-priceelasticityisanindexthatexpressesthisresponsiveness.Itistheratioofthepercentagechangeinquantitydemandedtothepercentagechangeinprice.Thisshouldbenegative,becausethedemandforcertainproductsnormallydecreasesasitspriceincreases.Iftheown-priceelasticityisgreaterthantheabsolutevalueof1,thedemandiscalled.Ifitislessthan1,demandisinelastic[Arelatedconceptiscross-priceelasticity,whichmeasuresthechangeinthequantitydemandedofonegoodinresponsetoachangeinthepriceofanothergood.Itcanbeeitherpositiveornegative.Positivecross-priceelasticityindicatesthatanincreaseinthepriceofXcausesthedemandforYtorise.Thisimpliesthatthegoodsare.Anegativecross-priceelasticityindicatesthatanincreaseinthepriceofXcausesadecreaseinthedemandforY,whichimpliesthatthegoodsarecomplements[ Table2Characteristicsofthe12articlesinthemeta-analysisandtheimpactonobesity,overweightandBMIAuthorPopulation(n)DatasetTypeofSSBsIndependentBarqueraS,etal.[1)Adolescents(n=416)1)MexicanNutritionSurveyAdolescents,1999SodaPriceAdults(n=2180)2)MexicanHealthandNutritionSurvey,20062)Adolescents(n=7464)3)TheMexicanhouseholdincomeandexpendituresurveys,1989,1998and2006SweetdrinksAdults(n=21113)3)Household(n=12000to20000)BonnetC,etal.[Household(n=19000)ConsumerpaneldataSoftdrinkPriceClaroRS,etal.[AllagesHouseholdfoodconsumptiondataSSBPrice(n=48470)2002-2003DharmasenaS,etal.al.42],USAHouseholdNielsenHomescanPanelNon-alcoholic1998to2003FinkelsteinEA,etal.al.18],USAHouseholdNielsenHomescanpanelCarbonatedSSBsPrice(n=384252)2006AllSSBsFinkelsteinEA,etal.al.47]USAAdultsandchildrenNielsenHomescanpanelSSBsPriceFletcherJM,etal.al.12],USAAges�18BehavioralRiskFactorSurveillanceSystemSoftdrinkTaxFletcherJM,etal.[Ages3to18(n=34000)NHANES1989and2006SoftdrinksTaxHanEandPowellLM.LM.23],USAFollow-upafterhighschoolMonitoringtheFutureSurveysSoftdrinkPrice(n=2400)1992-2003LinBH,etal.[],USAHousehold(n=22750)NielsenNationalConsumerPanelSugarydrinksPriceChildren219(n=7291Children)1998-2007DietdrinksAdults20andolder(n=8322)NationalHealthandNutritionExaminationPowellLM,etal.[Studentsfrom8th-10thMonitoringthefutureSurveycombinedwithstate-leveltaxdataandlocalareacontextualmeasure1997-2006Vendingmachine1200015000Studentsfrom12thgrade(n=30000)SmithTA,etal.[NielsenHomescanpanelistsCaloricsweetenedCabreraEscobaretal.BMCPublicHealth:1072Page4of10http://www.biomedcentral.com/1471-2458/13/1072 elasticitiesusingtherandomeffectsmodel(http://www.epigear.com).Afunnelplottestwasperformedtocheckforpossiblebiasintheown-priceelasticitiesincorpo-ratedinthemeta-analysis.Thestudiesreportingweightoutcomesweretooheterogeneoustobepooled.Figure1showstheresultsoftheliteraturesearch.First,of95articlesrelatedtoSSBs,43wereexcludedasthetitleorabstractindicatedthatthearticlewasnotrelatedtofiscalorlegislativepolicies.Second,outofthe52fulltextarticlesreviewed,20wereexcludedbecausetheyonlycommentedonSSBs(withoutmentionofanypol-icy)ordiscussedtaxesingeneral(notdirectlyrelatedwithSSBs).Oftheremaining32articles,15presentedquantitativedataandtheremaining17reportedqualitativedata(Figure1).Threefurtherarticleswereexcludedonthebasisofmissingdata(didnotreportstandarderrorandthedefinitionofSSBswasnotclear).Thesethreestud-ieswereperformedinGermany[41]andtwointheUSA[42,43].Thetwelvearticlesthatqualifiedforouranalysisre-portedown-priceelasticity,crosspriceelasticity,orimpactonobesity,overweightorBMI.Ninearticlesmetthecri-teriaforthemeta-analysis(Table2).TheremainingthreearticlesreportedonlytheimpactofSSBpriceonBMI,overweightand/orobesity.Allprimarydataconsistedofeithercrosssectionalorlongitudinalstudies.Therewerenointerventionstudies.Thestudieswerefromfourcoun-tries:USA,France,MexicoandBrazil.Allwerepublishedbetween2008and2013.Table3showstenestimatesofown-priceelasticityre-portedinnineofthestudies:sixfromtheUSA[18,47-51]andoneeachfromMexico[44],Brazil[46]andFrance[45].OfthestudiesperformedintheUSA,twousedtaxdataandfourpricedata,whilethestudiesperformedinMexico,BrazilandFranceusedpricedata.Alltheresultsshownegativeelasticity,whichmeansthatanincreaseinpricewasassociatedwithadecreaseinthedemandforSSBs.Ofthestudiesdoneinmiddleincomecountries,theoneinBrazilshowedanelasticityof0.85[46]andtheoneinMexico,-1.085[44].Theresultsfromthemeta-analysisshowthatthepooledelasticityestimateis1.30(95%CI:-1.089-1.509).Thefunnelplot(Figure2)fortheown-priceelasticitiesinthemeta-analysiswasroughlysymmetric,whichprovidesnoindicationofpublicationbias.Table3alsoshowscross-priceelasticitiesfromtheUSA[49,50]andMexico[44]Generally,theconsump-tionofSSBswascomparedwithwholemilk,fruitjuicesanddietsoftdrinks.ThedemandfortheseproductswasaffectedbySSBsprices.Forfruitjuices,themeta-analysisshowsacross-priceelasticityof0.388(95%CI:0.767),forwholemilkacross-priceelasticityof0.129(95%CI:-0.0850.342)andfordietsoftdrinksthe Table3OwnandcrosspriceelasticityofSSBsAuthor/year/countryOwn-priceelasticityCross-priceelasticityEstimatedSEFruitjuiceSEWholemilkSEDietdrinkSEBarqueraS,etal.(2008)(2008)44],Mexico1.0850.1950.0160.0030.0520.011BonnetC,etal.(2011)(2011)45],France2.2060.133ClaroRS,etal.(2012)(2012)46],Brazil0.850.434DharmasenaS,etal.(2012)(2012)42],USA2.2550.550FinkelsteinEA,etal.(2010)(2010)47],USA0.8700.090FinkelsteinEA,etal.(2013)(2013)18],USA1.3200.005FletcherJM,etal.(2010b)(2010b)48],USA4.4451.8061.8572.3327.672.156LinBH,etal.(2011)(2011)49],USA(Low-IncomePopulation)0.9490.0820.4730.1270.2420.1290.230.104LinBH,etal.(2011)(2011)49],USA(High-IncomePopulation)1.2920.0960.5290.0930.0540.130.5910.112SmithTA,etal.(2010)(2010)50],USA1.2640.0890.5570.0950.2220.1260.4570.1031.2990.3880.1291.089--1.509)(0.0095-0.767)(0.085-0.342)(0.628--1.219)Inallthenextfourcasestheauthorswerecontactedbyemailandcouldnotprovideanyadditionalinformationtoexplainthemissingvaluesneeded.Toinclusionofthestudies,weestimatedthefollowingvalues:Own-priceelasticity:Consumerpricesrosebymorethan3.4%onaveragewhichledtoadecreaseinmarketshareof7.5%.Then7.5/3.4=2.206.SEwasin-ferredfromTableVI:SE=(0.07/1.16)*2.206=0.133.Informationobtainedfromthepaper:P0.05atp(2-sides)=0.05.ThenSE=[0.85]/1.96=0.434.ThepaperdoesnotreportSE,butonlyap-valueof0.0000.ItwasusedawebsitetoderiveanestimateoftheZ-statistic(http://easycalculation.com/statistics/p-value-for-z-score.php).Itwaschoseavalueof4.1,whichisthelowestvaluethatgivesatwo-sidedp-valueof0.0000.ThenSE=[2.255]/4.1=0.550.SEinferredfrommeanandSEofgramsofsoftdrinkconsumption(Tableinref[]):mean=18.052,SE=7.333,Ratio7.33/-18.052=ThenSE=4.445*-0.40622=1.806.Thenumbersinparenthesisdenote95%confidenceinterval.CabreraEscobaretal.BMCPublicHealth:1072Page5of10http://www.biomedcentral.com/1471-2458/13/1072 cross-priceelasticityis0.423(95%CI:-0.628-0.219).ThismeansthatfruitjuicesandperhapswholemilkactassubstitutesforSSBs[44,45,52,53]anddietsoftdrinksareconsumedincomplementtoSSBs[44,48,49](SeeTable1fordefinitions).Table4showstheimpactonBMI,overweightandobesityduetoachangeinthepriceofdifferentSSBs.Itwasnotpossibletoperformameta-analysisbecauseofdifferencesininterventions,outcomesandpopulations(e.g.households,individuals-adults,adolescentsandchil-dren-aswellasdiverserangeoffoodstoresandvendingmachineoutlets).TheonlyavailableinformationwasfromtheUSA[12,23,47,50,52].Arangeofestimateswerere-ported,showingsignificantdiscrepancybetweenresults.HanandPowell[52]showthatfora1%increaseinSSBprice,thepointprevalenceforobesitywouldreducemoreinmen(0.34percentagepoints)thaninwomen([52].Smith,etal.[50]foundareductioninthepoint-prevalenceofoverweight(0.045percentagepoints)andobesity(0.03percentagepoints)inadults[50].Finkelstein,etal.[18]presentsdataathouseholdlevel,for20%increaseinSSBspricetheimpactonBMIwouldbe0.065kg/m2[47].ThenegativeimpactonBMIreportedbyPowell,etal.[23]isforspecifictaxes:theeffectofagrocerysodataxwasassociatedwithaBMIincreaseof0.012kg/m2andataxonsoftdrinkssoldviavendingmachineswitha0.011kg/m2increase.Theseeffectswerenotstatisticallysignificant[23].Fletcher,etal.[12]foundalowlevelofimpactinBMI(0.0031kg/m2)foradultsandanon-significantimpact(0.015kg/m2)inchildrenandadoles-cents[12,29].DiscussionThiscomprehensiveliteraturereviewsuggeststhatanincreaseinpriceofSSBsisassociatedwithadecreaseinconsumption;andthehigherthepriceincrease,thegreaterthereductioninconsumption.Also,asthepriceofSSBsrises,theconsumptionoffruitjuicesandwholemilktendstoincrease(althoughtheevidenceforthelat-tertrendisnotstatisticallysignificant),andthecon-sumptionofdietdrinksdecreases.ThefewavailablestudiessuggestthathigherpricesofSSBsmayleadtomodestreductionsinweightinthepopulation.Theintentionofthisstudywastoevaluatetheavail-ableevidenceworldwide.Thepooledown-priceelasti-citywas1.30(Table3).Theseresultsareconsistentwithothermeta-analysesincludingPowelletal.[18,37]whichfoundanown-priceelasticityof1.21;andAndreyeva,etal.[38]whichfoundanown-priceelasti-cityof0.79.BothofthesestudiesusedonlyUSAdata.Therewasinsufficientevidencetoundertakeaseparatemeta-analysisforLMICs.Thepossiblereasonsfortheown-priceelasticityout-lierresults[45,48]includethatfactthatoneofthestud-iesuseddatafromFranceandtheconsumptionpatternsmaydifferfromtheUSA.Context-specificevidencecanhoweverbeimportantbecausedifferentelasticitiescouldberelatedtoincomeorconsumerpreferences.SeveralstatesintheUSAhavealreadyimplementedanexcisetaxonSSBs,butthereisnoexperiencefrommiddleincomecountrieswheretheSSBmarketisgrow-ing.ResearchfromMexico[44]andBrazil[46]isbased Figure2Funnelplotofstudieswithown-priceelasticityofSSBsasoutcome. Table4Theimpactonobesity,overweightandBMIbasedinconsumptionchangeduetopriceincreaseofSSBsAuthor/year/countryImpactonBMISEImpactonSEImpactonobesityprevalenceSEPriceincrease(%)FletcherJM,etal.(2010a)(2010a)12]USAAdults-0.00310.00050.00020.00010.0001%FletcherJM,etal.(2010b)(2010b)48]USAChildrenandadolescents-0.0150.0160.0020.0110.0061%EA,etal.(2010)(2010)47]USA-0.0650.02320%HanE,etal.(2011)(2011)52],USA0.050.28710%HanEandPowellLM.(2011))52],USA0.340.38110%PowellLM,etal.(2009)(2009)21]USAVendingMachine0.0110.0171%PowellLM,etal.(2009)(2009)23]USAGroceryshops0.01240.01241%SmithTA,etal.(2010)(2010)50],USA0.045N/R0.03N/R20%BMIcalculation.Formula:Mass(kg)/(Height(m))^2=0.20kg/1.76m=.Massis0.20kg(Page5.Table.20%TaxoncarbonatedSSBs.Allgroups).Height:1.76(USAaverageheight).Notreported.CabreraEscobaretal.BMCPublicHealth:1072Page6of10http://www.biomedcentral.com/1471-2458/13/1072 onmodellingacorrelationbetweenpricesandconsump-tionandprovidesusefulinformationformiddleincomecountries,sinceitcanbeusedtoassesstheimpactoftaxes.Claro,etal.[46]presentedtwodifferentown-priceelasticities,forpoor(1.03)andnon-poor(0.63)(urbanandruralarea),whichsuggeststhatinBrazil,thepooraremoreprice-sensitivethanthemoreaffluent[46].TheevidencefromBrazilandMexicoisconsistentwithevidencefromhighincomecountries.Thisisimport-antinformationforpolicymakersinothermiddleincomecountries,whocanpotentiallydrawonthepooleddatauntillocalevidencebecomesavailable.Asurprisingfindingofthereviewwasthatthecon-sumptionofdietdrinksmaydecreaseasthepriceofSSBsincreases[54].Severalexplanationsarepossiblebutevidenceisscarce.Andreyevaetal.suggestthatbot-tlersand/orretailerscouldequalisepricesbetweenbothtypesofbeveragestocounteractthetax[43][REF].Peoplemayconsumedietsoftdrinksinthecompanyofpeoplewhoconsumesweetenedsoftdrinks,andifthepriceofthelattergoesup,bothmightswitchtoalternativebever-ages.MediareportsonthenegativeimpactofSSBsthataccompanynewtaxesmaychangeculturalnormsnotonlyforSSBsbutalsofordietdrinks,inasortofcontam-inationeffect.ReplacingSSBswithsugar-freebeveragesmaynotcompletelyavoidhealthproblems.Somestudiessuggestthattheriskofdevelopingmetabolicsyndromeincreasesby34%withhighconsumptionofdietsoda[55,56].Inthatlight,anegativecross-priceelasticitywouldbereassuring.However,althoughtheresultsofourmeta-analysisarestatisticallysignificant,thenegativecross-priceelasticityfordietdrinksreliesononlythreestudies,whichisnotastrongbasisforconclusions.Double-blind,randomisedclinicaltrialsinchildrenandadolescentsfindthatdrinkingsugar-freebeveragesratherthansugarcontainingbeverageshasthepotentialtosignificantlyreduceweightgainandbodyfatgain[32,57].Thereisgoodevidenceofanassociationbe-tweenSSBconsumptionandobesity.Inaddition,anin-creaseinpriceofSSBswouldlikelyreduceconsumption[18,44].ThissuggeststhattaxingSSBseffectivelycouldresultinreducedBMI,overweightandobesityamongpopulations.Smithetal.[50]showadecreaseinpointprevalenceforoverweight(0.045)andobesity0.03).Theauthorsarguethataminorreductionincal-oricintakewillchangetheweightclassificationoftheseadultsasmostofthemaremarginallyoverweightorobese.Likewise,adultswithahigherweeklyordailycon-sumptionwouldbeaffectedmorethanthosewhosecon-sumptionislower.Incontrast,anincreaseinweightwasfoundinthestudybyPowell,etal.[23]andamodestre-ductioninweightinthestudybyFletcher,etal.[48],buteachofthesestudiesraisesquestions.Thepositiveassoci-ationbetweentaxesandbodyweightthatPowell,etal.[23]presented,mayberelatedtotheanalysisfocusingonspecifictaxes,i.e.,avendingmachinesodataxratethatappearedassociatedwitha0.011kg/m2increaseinBMI.SuchtaxesmaynotbeeffectiveaspeoplemaypurchasetheirSSBsviaotheroutlets.Moreover,existinghighlevelsofobesityshouldhavepromptedtheimpositionoftaxesonallSSBsratherthanonspecificvendingmachineout-lets.Fletcheretal.[48]providesomeevidencethatsuchataxmayreducetheweightamongadolescentsatriskofoverweight,whilethereisnoobservedeffectonthosewithnormalweight.Onestudy[48]notesthattheimpactmaybeminimalbecauseofsubstitutionwithfruitjuiceandmilk.Thecaloriesinthesebeveragescouldreducetheef-fectofpriceincreasesonSSBs;juiceconsumptionasbeenassociatedwithweightgain[53].Evenso,aswitchtomilkandfruitjuicewouldstillcomewithahealthgainasthesedrinkscontaincalciumandvitamins.OverallthisreviewsuggeststhattaxingSSBsmaybenefithealth.PotentialmodelsfortaxingSSBscanbedrawnfromthetobaccoandalcoholexcisetaxexperi-ence.BecauseSSBsdonotprovideanynutritionalvalue,andwhenconsumedinexcesscanbeharmful,itseemsappropriatetoconsiderasimilarapproach.Thiswouldmeanthatthetaxisleviedasaspecifictaxforexampleexcisetax,suchasasumpergramofaddedsugar,raisingthenet-of-taxprice[45].Therearetwoimportantreasonsforconsideringataxonsugarcontent:Firstly,itwouldavoidsubstitutioninfavourofotherproductswithhighsugarcontent[45]andsecondly,itmightprovideanincentiveforindustrytoreducethesugarcontentofSSBs.Incontrast,ifthetaxisanadvaloremtax,thespecificvalueofthetaxwillbebasedonthecostoftheproductthuspermittingacompanytoreducethepre-taxpriceoftheirproduct,henceloweringthetaxlevelandundermin-ingitshealthimpacts(albeitattheexpenseofprofits).SSBpricehasbeenshowntohaveadoseresponserela-tionshipwithconsumption,withhighertaxesresultingingreaterreductioninSSBcalories[45,58,59].Thiscon-sumptioneffectmaybemitigatedbyconsumerssubstitut-ingproductssuchasmilkorfruitjuice.Analternativeoptionwouldbetotaxallsugarwhenitleavesthefactoryorentersacountry,usingtheargumentthatsuchataxmaybeeasiertoimplementandthatsugarconsumptioningeneralishigherthanisgoodforhealth[60].Chriquietal.[60]giveausefuloverviewofSSBtaxesappliedinju-risdictionsaroundtheworld.Taxesgeneraterevenue.Forexample,intheUSA,softdrinkrevenueisapproximately$70billionperyear,soamodesttaxwouldgeneratebillionsofdollars[48].Therevenuefromanexcisetaxcouldbeusedtosupportavar-ietyofobesityreductionprogrammes,schoolnutritionprogrammes,ortofinanceaHealthPromotionFoundation[61]thatcouldadvocateforhealthyeatingincludingfur-therreductionsintheconsumptionofSSBs.AtaxmightCabreraEscobaretal.BMCPublicHealth:1072Page7of10http://www.biomedcentral.com/1471-2458/13/1072 alsobeusedtosubsidisealternativehealthydrinkstore-ducetheirpriceandthusencourageconsumption[62,63].InareaswherepeopledrinkSSBsbecausetheydonothaveaccesstocleanwater,ensuringuniversalaccesstoclean,pipedwatershouldbeapriority.Oneargumentagainsttheimpositionofanexcisetaxaloneisthatitisregressive[12,49,64].Lower-incomehouseholdstendtospendagreaterportionoftheirin-comeonconsumablegoodsthanhigher-incomehouse-holds.Relativetoincome,aSSBtaxwouldthereforeaffectlow-incomepeoplemorethanhigh-incomepeople.How-ever,lowincomehouseholds,asagroup,arealsolikelytoreapgreaterbenefit.Totheextentthatlow-incomeindi-vidualsaremorepricesensitive,theywillbemorelikelytocutbackontheintakeoftaxedSSBs,oftenfromahigherconsumptionlevelandwithahigherBMI,andthusex-periencegreaterhealthgain[64].Thisgivesgroundtoconsiderasimultaneoussubsidyofhealthyfoodssuchasfruitandvegetables.Inthepast,thosemostsusceptibletoobesityandcardiovasculardiseaseswereamongthewealthierinthepopulationbutthisisnolongerthecase.Lowincomeearnersarenowapopulationwithhighcon-sumptionofunhealthyobesogenicfood[65,66].AlsoinmanyLMICs,theprevalenceofobesityisgrowingmorerapidlyinlowsocioeconomicgroups[67].Upcomingresearchshouldestimatepriceelasticitiesinlow-andmiddle-incomecountriesandidentifypotentialhealthgainsfromtaxescombinedwithsubsidiesofhealthyfood.Asfarasweknow,thisisthefirstglobaloverviewoftheeffectofSSBpriceonconsumptionandbodyweightand,intheabsenceofgoodqualitylocalevidence,mayinformpolicydecisionsworldwide.Thelimitationsaretwofold.First,inLMICs,consumptionpatternsandpricesensitivitiesmaydifferfromHIC(althoughtheevidencefromMexicoandBrazildoesnotsupportthis).Secondly,thedataincludedinthemeta-analysisarefromheteroge-neouspopulationswithvariousdatasourcesinvolvinghouseholds,individuals(adults,adolescentsandchildren)aswellasadiverserangeoffoodstoresandvendingmachineoutlets.ConclusionsAnincreaseinpriceofSSBsisassociatedwithadecreaseinconsumption;andthehigherthepriceincrease,thegreaterthereductioninconsumption.Also,asthepriceofSSBsrises,theconsumptionoffruitjuicesandwholemilktendstoincreaseandtheconsumptionofdietdrinksde-creases.ThealternativebeveragesaremostlikelybetterforhealththanSSBs.ThefewavailablestudiessuggestthathigherpricesofSSBsmayleadtomodestreductionsinweightinthepopulation.Thisevidenceandthelinkbe-tweenobesityandSSBsanditshealthoutcomesshouldbesufficientforpolicymakerstoconsiderSSBtaxationaspartofapackageofinterventiondesignedtoreducethehealthandeconomicburdenduetoobesity.Futurere-searchshouldaddresstheconsequencesofataxonSSBs,includingthehealthgains,populationaffectedandtheim-pactonthemacroeconomicenvironmentincludingjobs,monetarysavingstothehealthsector,implementationcostsandrevenuegeneratedforthegovernment[68].Fullcost-effectivenessstudieswouldprovidestrongerevidenceandallowpolicymakerstoweighthesefactors.Toenhancerelevanceforanyparticularjurisdiction,suchstudiesshouldusedataspecifictothecountriesorsub-regions,andbeundertakenwithsoundunderstandingofcontext-specificpolicies,historyandsocio-culturalpreferences.Sugarsweetenedbeverages;LMICs:Lowandmiddleincomecountries;NCDs:Non-communicablediseases;HICs:Highincomecountries;GBD:TheGlobalBurdenofDisease;NBER:NationalBureauofEconomicsResearch;RePEc:ResearchPapersinEconomics.CompetinginterestsTheauthorshavedeclaredthatnocompetinginterestsexist.ThecontentoftheworkpresentedhereissolelytheresponsibilityoftheauthorsanddoesnotnecessarilyrepresenttheofficialviewsoftheIDRC.MC:Performedtheliteraturereviewandpreparedthefirstdraftofthemanuscript.LV:Supervisedthemeta-analysisandprovidedcommentsonalldraftsofthemanuscript.ST:Providedcommentsonthemanuscriptandcrit-icallyreviseditforimportantintellectualcontent.MB:Contributedtotheconceptionofthestudy,supervisedtheinitialliteraturereviewandprovidedcriticalcommentsonseveraldraftofthemanuscript.KH:Madesubstantialcontributionstotheconceptionofthestudy,providedcriticalcommentstoalldrafts.AllauthorshavegivenfinalapprovalofthemanuscripttobeAcknowledgmentsWewishtoacknowledgethesupportofPatriziaFaviniinpreparingtheThisresearchwassupportedbygrantPROP020911EfromtheIDRC,Canada.Thefundershadnoroleinstudydesign,datacollectionandanalysis,decisiontopublish,orpreparationofthemanuscript.AuthordetailsPRICELESSSA(PriorityCostEffectiveLessonsinSystemStrengtheningSouthAfrica),Johannesburg,SouthAfrica.SchoolofPopulationHealth,TheUniversityofQueensland,Brisbane,Australia.Wits/MedicalResearchCouncilRuralHealthandHealthTransitionsUnit,SchoolofPublicHealth,FacultyofHealthSciences,UniversityofWitwatersrand,Johannesburg,SouthAfrica.Received:30April2013Accepted:23October2013Published:13November20131.WorldHealthOrganization:ReportofaJointWHO/FAOReport.Diet,NutritionandthePreventionofChronicDiseases.Geneva:WHOtechnicalreport;2002.2.JamesWPT:WHOrecognitionoftheglobalobesityepidemic.IntJObes3.MalikVS,WillettWC,HuFB:Globalobesity:trends,riskfactorsandpolicyNatRevEndocrinol4.SwinburnBA,SacksG,HallKD,McPhersonK,FinegoodDT,MoodieML,GortmakerSL:Theglobalobesitypandemic:shapedbyglobaldriversandlocalenvironments.5.ChaputJP,TremblayA:Obesityandphysicalinactivity:therelevanceofreconsideringthenotionofSedentariness.ObesFacts6.LimSS,VosT,FlaxmanAD,DanaeiG,ShibuyaK,Adair-RohaniH,AlMazroaMA,AmannM,AndersonHR,AndrewsKG,AryeeM,AtkinsonC,BacchusLJ,CabreraEscobaretal.BMCPublicHealth:1072Page8of10http://www.biomedcentral.com/1471-2458/13/1072 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Submit your next manuscript to BioMed Central and take full advantage of: Convenient online submission Thorough peer review No space constraints or color gure charges Immediate publication on acceptance Inclusion in PubMed, CAS, Scopus and Google Scholar Research which is freely available for redistribution Submit your manuscript at www.biomedcentral.com/submit CabreraEscobar etal.BMCPublicHealth 2013, 13 :1072Page10of10 http://www.biomedcentral.com/1471-2458/13/1072