In other words, the paradox is in the timing. It may be that soy consumption is protective (against breast cancer) only if started before cancer develops.
The articles on genistein linked below and its effect on breast cancer are excellent. The articles give very good descriptions of what genistein is and how it works in the body. I am including it in the breast cancer section because there is so much controversy about the use of soy products by those with breast cancer. Included below is what the article says about genistein and breast cancer, but the entire free full-text article deals with its effect on many other cancer types. A pop-up of the full article will appear by clicking on the link below.
Mary Miller- Breast Cancer Profile in Courage
Ed. Note- My name is David Emerson. I am the Director of PBC. I added the article below on 1/11/18 because the content is relevant to the post below.
“Dietary xenoestrogens drastically reduce the effectiveness of palbociclib plus letrozole in the treatment of patients with BC, according to a study published in Cell Chemical Biology…
Results showed that genistein and zearalenone antagonized the metabolic effect of palbociclib plus letrozole in BC cells. Upon exposure to either xenoestrogen, cancer cells returned to a level of activity similar to that of before treatment…”
“To eat soy or not: That’s the question many U.S. women have been asking. Tofu, miso paste, and other soybean-based foods are high-quality sources of protein that are low in calories and saturated fat. And studies have shown that they can help prevent cancer.
Yet many doctors recommend that women who have or are at risk of developing, a common form of breast cancer called estrogen-receptor-positive breast cancer avoid eating soybean-based foods because they contain compounds called isoflavones. Some studies suggest that isoflavones can mimic the hormone estrogen and encourage tumor growth…
The study may explain why women in Asian countries, who tend to consume high amounts of soybean-based foods throughout their lifetime, have rates of breast cancer that are five times lower than those of women in the United States…
In their animal study, the researchers induced cancer growth in rats that had a steady diet of genistein and in rats that never had any genistein until after the cancer developed. All of the rats were then treated with tamoxifen to kill the cancer. The researchers found that the rats raised on genistein had only a 7 percent chance of breast cancer recurrence after tamoxifen treatment, but the rats that were recently given genistein had a 33 percent recurrence rate…
In other words, the paradox is in the timing. It may be that soy consumption is protective only if started before cancer develops.
Despite the lingering ambiguity of whether the same is true in humans, Hilakivi-Clarke thinks the animal study can inform doctors and their patients.
“We have solved the puzzle of genistein and breast cancer in our rat model, which perfectly explains the paradox seen in earlier animal studies and patients,” Hilakivi-Clarke said. “While many oncologists advise their patients not to take isoflavone supplements or consume soy foods, our findings suggest a more nuanced message — if these results hold true for women. Our results suggest that breast cancer patients [who ate soy before their diagnosis] should continue consuming soy foods after diagnosis, but not to start them if they have not consumed genistein previously…”
“Interest in genistein as a potential therapeutic agent has recently risen in the field of oncology as population-based studies have linked genistein consumption with a decreased risk of mortality from several types of cancer, most notably prostate and breast cancer [3
Population-based studies have linked decreased cancer incidence to increased genistein consumption for several cancer types, with most studies focused on prostate or breast cancer
In breast cancer, genistein consumption has been associated with a decrease in disease incidence
], potentially as a result of genistein’s ability to mimic natural estrogens (see Section 2.1
), which are known to play a role in breast cancer progression…
Multiple groups have also demonstrated that genistein can inhibit invasion of breast cancer cells
]. In one study, the authors proposed that decreased invasion with genistein treatment was a result of decreased production of MMPs (see Section 3.4
), although an exact molecular target was not discussed [137
]. A second study demonstrated that genistein is able to downregulate the levels of the chemokine receptors CXCR4 and CXCL12 when the breast cancer cells were treated with low micromolar concentrations of genistein [162
]. These receptors direct the homing of primary cancer cells to a metastatic site and can also alter cellular adhesion…
Genistein has also been extensively studied in mouse models of breast cancer. However, genistein’s weak estrogenic activity (see Section 2.1) has been the central focus of these studies, as breast cancer is known to be hormonally responsive.
These studies indicate that the effect of genistein upon breast cancer is dependent upon the nature of the estrogenic environment in which the study is conducted. If endogenous estrogen is low, genistein can bind the ER receptor and exert pro-growth effects upon responsive systems. If endogenous estrogen is high and potent, genistein can act as a competitor to estrogen and thus antagonize this hormone’s pro-growth effects (reviewed in [171
]). Therefore, while genistein has shown promise as an anticancer agent for breast cancer, the results are much more complex and dependent on hormone levels than those for prostate cancer
Conclusion- Genistein is a biologically important isoflavone that is found in high amounts in soy products. This small compound has garnered a great deal of attention in the field of oncology research, as it exerts a wide range of biological effects of direct relevance to cancer. In particular, genistein has proven to be a valuable tool for the inhibition of cancer metastasis, exerting effects on both the initial steps of primary tumor growth as well as the later steps of the metastatic cascade…