Equolisfirstisolatedandidentifiedfrompregnant-mares'urineandlaterfoundintheurineofthegoat,cow,henandsheep.Equol,unlikethesoyisoflavonesdaidzeinorgenistein,hasachiralcenterandthereforecanoccuras2distinctdiastereoisomers.S-equolistheexclusiveproductofhumanintestinalbacterialsynthesisfromsoyisoflavonesandbothenantiomersarebioavailable.S-equolhasahiChemicalbookghaffinityforestrogenreceptorbeta(Ki=0.73nM),whereasR-equolisrelativelyinactive.EquolcouldpromotetheproliferationanddifferentiationofratosteoblaststhroughactivatingtheER-PKCα-relatedsignalingpathway.Thealkalinephosphataseactivityalsoincreasessignificantlyinalloftheequoland17β-estradiol(E2)groups.Equolalsosignificantlyelevatestheosteocalcinlevels.