soybean and phytoestrogen?

"plagiarized" from wikipedia.

Phytoestrogen

Main article: Phytoestrogens

Soybeans contain isoflavones called genistein and daidzein, which are one source of phytoestrogens in the human diet. Because most naturally occurring estrogenic substances show weak activity, normal consumption of foods that contain these phytoestrogens should not provide sufficient amounts to elicit a physiological response in humans.^{[citation needed]} However, animal studies have shown significant physiological responses, and many people's consumption of soy products (especially vegetarians and infants on soy formula) could far exceed what most studies would consider "normal" consumption.

Plant lignans associated with high fiber foods such as cereal brans and beans are the principal precursor to mammalian lignans which have an ability to bind to human estrogen sites. Soybeans are a significant source of mammalian lignan precursor secoisolariciresinol containing 13–273 µg/100 g dry weight.^[39] Another phytoestrogen in the human diet with estrogen activity is coumestans, which are found in beans, split-peas, with the best sources being alfalfa, clover, and soybean sprouts. Coumestrol, an isoflavone coumarin derivative is the only coumestan in foods.^[40][41]

Soybeans and processed soy foods do not contain the highest "total phytoestrogen" content of foods. A study in which data were presented on an as is (wet) basis per 100 g and per serving found that food groups with decreasing levels of total phytoestrogens per 100 g are nuts and oilseeds, soy products, cereals and breads, legumes, meat products, various processed foods that may contain soy, vegetables, and fruits.^[42]

[edit]Men

Because of the phytoestrogen content, some studies indicate that there is an inverse correlation between soybean ingestion and testosteronein men.^[43] For this reason, they may protect against the development of prostate cancer.^[44] A theoretical decrease in the risk of prostate cancer should, however, be weighed against the side-effects of decreased testosterone, including diminished libido.