Breast cancer and prostate cancer can be caused by sex hormones. In particular breast cancer may be caused by high levels of oestrogen. As well as being a sex hormone, oestrogen is a hormone that stimulates the proliferation of cells. It is in this role that it is believed that oestrogen may increase the risk of developing breast cancer. Reducing or blocking the effects of oestrogen may therefore be beneficial at preventing the proliferation of cancer.
Tamoxifen is the current drug of choice for women with estrogen responsive breast cancer. Tamoxifen is used because it has anti-oestrogenic properties. Because tamoxifen is a similar shape to oestrogen molecules, it can fit in the oestrogen receptor. However, it does not activate the receptor like estrogen, but instead sits in the receptor blocking the action of oestrogen to cause cell proliferation. In this way tamoxifen can reduce the impact of oestrogen in the body.
Any molecule with a similar shape to oestrogens may at to block its action. Many plant compounds have an oestrogenic structure, and as a result are referred to as phytoestrogens. Three phytoestrogens are of particular interest because evidence suggest that may decrease the risk of breast cancer when consumed regularly in the diet. These are genistein, daidzein and glycitin, all of which are found in the soya bean and belong to the class of chemicals called isoflavones.
Soya And Cancer Risk
Asians eat a lot of soya products including miso and tofu. Epidemiological studies show that Asians have lower rates of breast cancer than those living in the West, and some have attributed this protection to the soya they eat. The phytoestrogens in soya might act like tamoxifen, binding to the oestrogen receptor, but not activating a response. Instead the phytoestrogen blocks the action of oestrogen, lowering its effects in the body.
Genistein And Cancer
Cell culture experiments suggest that genistein is the most beneficial phytoestrogen in soya. Because of this some have recommended consuming genistein as an isolated compound to protect from breast cancer. However, this may be problematic because there is no safety data for consumption of isolated compounds from soya. If Asians are protected from cancer, it is because they eat whole soya beans and its products, not isolated compounds.
Recently soya has infiltrated the Western food supply. Soya is now routinely added to many food under the guise of textured vegetable protein, including food such as tinned tuna. Soya milk is also available and many choose to consume it. However, the benefits of consuming soya in these ways are not understood. Asians receive protection from eating their traditional products such as tofu and miso. For cancer prevention, it is important to therefore consume the same foods as in Asia.