The effectiveness and safety of phytoestrogens are still
unclear. A current review study indicates that phytoestrogen intake is without serious adverse
events [58]. Studies also
described the benefits of phytoestrogens on cancer and
cardiovascular diseases. Epidemiological studies suggest that dietary phytoestrogen intake is
associated with a reduced risk of endometrial and prostate cancers [59,60]. A case-control study
indicates that isoflavones intakes were inversely associated with ovarian cancer risk [61]. Current
data of humans and animals provide evidence for several anticancer properties of soy and/or its
isoflavones [62]. In addition, the consumption of soybean oil may have a role in retarding
atherosclerosis and the risk of cardiovascular disorders associated with estrogen deficiency in
estrogen loss [63]. Genistein may also decrease arterial pressure and prevent the development of
heart disease due to antiproliferative and proapoptotic effects on vascular cells [64].
However, excessive phytoestrogens consumption may also lead to adverse health effects. Laboratory
studies in animals have demonstrated the potential for adverse effects after exposure to high
levels of soy isoflavones [65]. Studies also show that the extensive use of supplemental
phytoestrogens is shown to cause grade 1 endometrioid adenocarcinoma of the endometrium [66].
Mlynarczuk et al [67] found that coumestrol impairs secretory function of the corpus luteum, and in
this way, it can affect the maintenance of pregnancy in the cow. Furthermore, supplementing with
resveratrol exac- erbates both autoimmune and viral models of multiple sclerosis [68].
Despite the generally positive effects of phytoestrogens, further studies are needed to investigate
their adverse effects. Ideally, studies to examine the effects of phytoestrogens on humans would be
done in human subjects, but concerning both the complicated design and interpretation of human