(S)-Equol is an estrogen receptor beta (ERβ) agonist, formed in some people by intestinal bacteria from the soy phytoestrogen daidzein. (S)-Equol has approximately 13-fold higher affinity for human ERβ over ERα and an EC50 value of 65nM for ERβ compared to an EC50 value of 85nM for ERα. It has been shown to have anti-inflammatory and neuroprotective activty.