Phytoestrogens are secondary plant compounds. They owe their name to their estrogen-like properties or effects, because they are structurally similar to steroidal estrogens synthesized (formed) in the body. The phytoestrogens can bind to estrogen receptors, thereby producing both estrogenic and antiestrogenic effects. The effect of phytoestrogens is only 0.1% of endogenous (body’s own) estrogens.
The best known phytoestrogens are:
- Lignans
- Isoflanvonoids (synonym: isoflavones)
Both groups belong to the polyphenols.
Phytoestrogens are attributed anticarcinogenic (cancer-protective) effects. This applies primarily to the hormone-related tumor diseases mammary carcinoma (breast cancer), endometrial carcinoma (uterine cancer) and prostate carcinoma (prostate cancer). Colon carcinoma (colorectal cancer) and bronchial carcinoma (lung cancer) are also mentioned in this context. In Asia, for example, the risk of hormone-dependent tumor diseases is lower, which is attributed to the high proportion of soy products in the Asian diet.
Phytoestrogens exert a positive influence on the following stages of tumor development:
- Initiation (stage 1)
- Promotion (phase 2)
- Anti-estrogen effect
- Progression (phase 3)
- Inhibition (delay/inhibition) of blood vessel formation.
Furthermore, phytoestrogens have an antioxidant effect. Here, especially the isoflavonoid genistein is so far well studied. This inhibits both the formation of oxidative damage to the genetic material and the peroxidation of triglycerides and LDL cholesterol.
Occurrence
Isoflanvonoids are found primarily in tropical legumes, such as soybeans, and products made from them, such as tofu. The estimated daily intake is more than 5 mg.
Lignans represent the starting substance for the synthesis (bioling) of lignins. Main sources of lignans are flaxseeds and pumpkin seeds. Other lignan-rich foods include cereals, low-mix cereal flours, and cereal bran.
