Equol (4'7-isoflavandiol) is an isoflavandiol estrogen metabolized from daidzein a type of isoflavone found in soybeans and other plant sources by bacterial flora in the intestines. While endogenous estrogenic hormones such as estradiol are steroids equol is a nonsteroidal estrogen. Only about 30–50% of people have intestinal bacteria that make equol. (S)-Equol was first isolated from horse urine in 1932 and the name was suggested by this equine connection. Since then equol has been found in the urine or plasma of many other animal species although these animals have significant differences in their ability to metabolize daidzein into equol. In 1980 scientists reported the discovery of equol in humans. The ability of (S)-equol to play a role in the treatment of estrogen- or androgen-mediated diseases or disorders was first proposed in 1984.