The phytochemical genistein belongs to a class of compounds called isoflavones found in many plants. Genistein is found mainly in the soybean plant from which tofu and other soy products are made. Isoflavones are said to have string antioxidant properties although some studies suggest that genistein has actually the opposite (oxidation) effect.
In addition, genistein has been shown to interact with human estrogen receptors, and can mimic effects similar to those of estrogen. Recently, the US FDA has approved over-the-counter soya-based supplements as an alternative to hormone replacement therapy for menopausal women.
This review paper by researchers at the Georgetown University tries to answer whether genistein promotes or inhibits the formation of tumors in breast cancer. This topic sparked interest when it way observed that breast cancer is lower among Asian women compared to white women. However, this risk cannot be explained solely by genetic and ethnic factors because Asian women who migrated to the US tended to develop the risk level of Caucasian women within 2 generations. There is therefore, a strong possibility that lifestyle change -especially diet – may play an important in this increased risk.
Asian diet is rich with tofu and other soy products. Soy products have long been though to be a wonder health food that is beneficial to cardiovascular health although many experts believe otherwise. Over the years, numerous studies on the health effects of soy products have been conducted with contradicting or inconclusive results.
The conclusions of the review paper are as follows:
- Genistein has both carcinogenic and anticarcinogenic potential and timing is a critical factor in determing its effects on breast cancer development
- Genistein’s effects may depend on estrogen levels. “It is plausible that genistein has different effects on the breast in the presence of high estrogen levels (such as during pregnancy), moderate levels (such as during premenopausal life), and low levels (such as during childhood and postmenopause).”
- It is clear from epidemiologic data that Asian women living in Asia (where a diet high in soy is consumed) have a decreased risk for breast cancer. One possible explanation for the apparent lack of tumor-promoting effects of genistein in Asian populations is that a lifetime exposure to genistein may have a protective effect. It is also possible that soy contains other factors besides genistein that oppose the estrogenic effects of genistein and actually reduce breast cancer risk. Additionally, other environmental or lifestyle factors may be more related to the low breast cancer risk seen in this population than soy/genistein consumption.
It is clear that more research is needed before the truth about genistein is to be known. In the meantime, we should keep in mind that breast cancer development is not only due to diet but due to other lifestyle as well as environmental factors.
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