NONSTEROIDAL ESTROGENS OF DIETARY ORIGIN - POSSIBLE ROLES IN HORMONE-DEPENDENT DISEASE

Equol, a nonsteroidal estrogen of dietary origin, was recently identified in human urine, and is excreted in amounts comparable to the classical steroidal estrogens. Phytoestrogens which are abundant in dietary soy protein are converted by human gastrointestinal flora to this weak estrogen. After the ingestion of meals containing cooked soy protein the urinary excretion of equol in 4 of 6 subjects studied increased by up to 1000-fold and this compound was the major phenolic compound found in the urine. These data also indicate that some subjects are unable to either produce or excrete equol despite the challenge of a diet containing soy. In view of the increasing use of commercial soy products in the diet and the capacity of human bacterial flora to synthesize this weak estrogen from the abundance of phytoestrogens in soy, the potential relevance of these observations to the diseases implicating steroid hormones is discussed.