Gut Microbiota and the Metabolism of Phytoestrogens

Gut microbiota have a variety of health and nutritional benefits in their host organisms. Their beneficial effects are related to gastrointestinal diseases, immunomodulation, intestinal microbial balance, and antimicrobial properties. However, their properties also involve an influence on the bioavailability of certain drugs and food components in the body. Phytoestrogens are nonsteroidal secondary metabolites with estrogenic activity. They are found in various foods, especially soy, and are used for the treatment of estrogen-associated diseases such as menopause, cardiovascular diseases, breast cancer, and osteoporosis. Some metabolites produced by gut microbiota from phytoestrogens have even stronger effects due to their higher lipophilicity, which leads to a better absorption and a higher affinity with estrogen receptors. The crucial metabolism of phytoestrogens takes place in the gastrointestinal tract where the gut microbiota are present. Probiotics are live microorganisms that can confer health benefits to the host when administered in adequate amounts. They are present in milk products and dietary supplements, and are capable of restoring the gut microbial communities when ingested. Most of the probiotics are bacteria and thus their intake can enhance the metabolism of phytoestrogens and, therefore, enhance their pharmacological effects. In this review, we summarize the influence of gut microbiota on the metabolism of phytoestrogens and their beneficial effects on the host.