The study is a double blind, randomized, placebo-controlled, dose-escalation study of the safety and tolerability of single doses of S-equol up to 320 mg in healthy male and female adult subjects. Approximately 8 qualified volunteers will be selected at each dose level and randomly assigned to receive S-equol or placebo, in the fasted state. For the 20 mg dose group, subjects will complete two treatment periods, one in the fasted state, and one in the fed state.