Soy phytoestrogens: hormonal activity and impact on the reproductive system
Phytoestrogens (PhE) are contained in soy and some other plants; they are structurally similar to estrogens. PhE are used for substitution therapy in the menopause. However, some recent reviews concluded that no satisfactory evidence has been provided in favor of PhE efficiency against menopausal symptoms compared to placebo. Soy is used as an ingredient of infant food and other foodstuff as well as cattle fodder, so that residual PhE and their degradation products, e.g. equol, having estrogenic activity, can remain in meats. Soy protein is used in the food industry. Disorders of the reproductive system in humans under the influence of PhE are regarded to be rare and mild. There were single reports on altered gender-related behavior in children and feminization associated with soy consumption. In animals, the excessive PhE intake leads to derangements of fertility, sexual development and behavior. PhE are called modulators or disruptors of the endocrine system. There are no reasons to assume that benefits from such modulation would prevail in all soy consumers. Feminizing effects may be inconspicuous but statistically detectable in large populations.