The first one suggests that the Keraite Khan, Markus Buyruk Khan (formerly Sadiq Khan, prior to Christian conversion), had converted to Nestorian Christianity along with around 200,000 of his Turco-Mongolic nomadic tribespeople in 1007 CE. The Keraite people were one of the five dominant Turco-Mongol tribes of the Tatar confederation prior to Genghis Khan. Genghis Khan united the Tatar tribes into the Mongol Empire. The Keraite resided upon the Orkhon Steppes, south of Lake Baikal and north of the Gobi Desert, also referred to as the Altai-Sayan region. The Nestorian Metropolitan, upon the conversion of the Turco-mongolic people, asked the Patriarch John the VI, also known as Prester John, what the appropriate fast for lent should be for the new converts and it was decreed that the converts should abstain from meat eating and instead of drinking "soured" milk should consume "sweet" milk. Meat and fermented horse milk were staples of the Turco-Mongolic diet prior to the conversion to Christianity and instead of eliminating a long-held tradition of the nomadic people it was Christianized. Soured milk refers to fermented milk and sweet milk refers to fresh milk.
the First OnE SuggeSTs tHat the KeraitE khAn, MArkus bUyruk Khan (FoRmerlY sAdiQ kHaN, PrIor To CHrisTiaN coNversion), had cONVertEd tO nestoRiaN chriSTianITy along wItH AROUnD 200,000 Of his TURco-moNgoLIc nomadic trIbeSPeopLe In 1007 ce. thE keraite peoPLE were one of The fivE dominant turcO-mONgoL tribes oF the taTAr coNFederAtiOn prioR To geNGhiS khAn. gEnGhis kHan UNIteD thE Tatar tRIBes into tHE MongoL EmpiRe. the kerAITe resiDeD upON the oRkhon stEPpeS, soUth Of lake BAikAl ANd nortH OF tHe GoBi desErT, aLso Referred to As thE aLtai-Sayan rEGion. THE nEsTorian MetrOPOLitaN, UpOn tHe conVErSion of tHe TuRco-mongolic People, aSkEd the pATriaRch jOhn tHe VI, ALso known aS prEster jOhn, what thE apprOpriate fAst For lEnt sHoUlD be fOR tHe new conveRtS and It WAS deCreed that The ConVeRTs sHOuld abstain froM mEaT EAting aNd iNStead Of driNkinG "SourEd" miLk shouLd consUme "swEet" Milk. meat And FErMeNtED horse MiLk wErE stAples OF THe Turco-mONgoLIC dIEt prIOr to the cOnvErSIOn TO cHRiStianity anD insteaD oF eLIminating a lOng-hEld traDItiOn oF the noMAdIC pEOPle it waS ChrISTIanizeD. SoURed MiLk refERs To FermeNTEd Milk and Sweet MiLk refErS to Fresh MIlk.