Phytoestrogens have been promoted as healthy dietary supplements and foods, such as soybean-derived foods, rich in the isoflavones genistein and daidzein. These isoflavones are also found in soy-based infant formulas. 
Phytoestrogen groups: Isoflavones (genistein, daidzein, glycitein, formononetin), flavones (luteolin), coumestans (coumestrol), stilbenes (resveratrol) and lignans (secoisolariciresinol, matairesinol, pinoresinol, lariciresinol). Isoflavones are found at high concentrations in soybean products whereas lignans are found in flax seed, coumestans are found in clover, and stilbenes are found in cocoa- and grape-containing products, particularly red wine.
Jefferson, Patisaul and Williams 2012 write that many studies provide evidence that phytoestrogen exposure can impact the reproductive health, depending on the dose, route of exposure, and the timing of exposure beginning in the early prenatal period. The authors caution that more phytoestrogens are recognized or developed as therapeutic compounds, and are placed on the food market as supplements. The researchers call for careful study of the effects of phytoestrogens on the reproductive system, as negative effects are known.
 Jefferson WN, Patisaul HB, Williams C: Reproductive consequences of developmental phytoestrogen exposure. Reproduction. 2012 Jan 5