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1、1.Greedyguts?（TheEconomistsJan4th,2007）ALTHOUGHmostpeopleprefernottothinkaboutit,humangutsarefullofbacteria.Andagoodthing,too.Theseintestinalbugshelpdigestion,andalsostoptheirdisease-causingcounterpartsfrominvading.Inreturn,theirhumanhostsprovidethemwithawarmplacetoliveandash
2、areoftheirmeals.Nowitisworkingrathertoowell.AgroupofresearchersledbyJeffreyGordon,oftheWashingtonUniversitySchoolofMedicine,inStLouis,hasfoundthatsometypesofmicrobesarealotbetterthanothersatprovidingusablefoodtotheirhosts.Inthepast,whenfoodwasscarce,thosewhoharbouredsuchmicro
3、beswouldhavebeenblessed.Thesedays,paradoxically,theyarecursed,fortheextrafoodseemstocontributetoobesity.DrGordon’sresearchisoutlinedinapaperpublishedinthisweek’sProceedingsoftheNationalAcademyofSciences(PNAS)andtwootherspublishedlastmonthinNature.IntheNaturepapers,heandhistea
4、mreportedthatobesepeoplehaveadifferentmixofgutmicrobesfromthatfoundinleanpeople—amixthatismoreefficientatunlockingenergyfromthefoodtheyconsume.TheresearcherssequencedbacterialDNAfromfaecalsamplestakenfromvolunteersanddiscoveredthatthosewhowereobesehadahigherproportionofFirmic
5、utesthanleanpeopledid.BugsinthesystemThisalsoturnedouttobetrueinmice,andworkingwiththeserodents,theresearchersdiscoveredthatthetypesofFirmicutefoundinobeseanimalsaremoreefficientatconvertingcomplexpolysaccharidesintosimple,usablesugarssuchasglucose.Ineffect,theFirmicutesmadem
6、oreenergyavailablefromthesameamountoffood.Theresearcherswereevenabletomakemicethathadbeenraisedinagerm-freeenvironmentfatterorthinnerbycolonisingtheirgutswithmicrobesfromeitherobeseorleanmice.Itsoundssimpleenough.Unfortunately,furtherprobingshowedthatthestoryisalittlemorecomp
7、licated,forDrGordondidnotmerelycountthegutbacteriaoffatandthinpeople—hethenputsomeofthefatonesonadiet.Astheseonce-obesehumanslostweightoverthecourseofayear,theirmixofgutmicrobeschangedtoreflecttheirnew,sveltestatus.Whythishappenedisnotclear.Itdoesnotseemtohavebeenaresultofthe
8、compositionofthediet,sincetheeffectwasthesamewhetherpeoplelostweight
