Written by Dr. Patrick Massey, MD, PhD. Dr. Massey believes that future research will conclusively show that a diet rich in phytoestrogen-containing foods lowers the risk of breast cancer recurrence as well as improves survival.
Years ago, it was discovered that most breast cancer cells have receptors that bind the hormone estrogen. Research revealed that if animal estrogen attached to these receptors, breast cancer cells grew faster. Since this discovery, much of the medical therapy for breast cancer has focused on limiting the binding of estrogen to estrogen receptors, and this approach has been very successful.
Plants also make estrogen-like molecules called phytoestrogens. Phytoestrogens do not bind to the estrogen receptor in the same way as animal estrogen and some researchers believed that these plant estrogens could prevent animal estrogen from binding to breast cancer cells and prevent cancer growth.
However, early research, done in test tubes and in mice, suggested that even plant estrogens could stimulate breast cancer cells to grow. Based on this research, it was suggested that those with breast cancer should avoid plant estrogens, especially soy, because soy has a generous amount of phytoestrogens.
Yet, that was not the end of the story. Epidemiological medical research suggested that phytoestrogens in the diet actually prevented breast cancer. Some theorized that the laboratory research was flawed and that dietary soy may be beneficial for breast cancer patients.
A recent study, conducted through Vanderbilt University and published in the Journal of the American Medical Association has shed some light on this controversy. The study set out to compare survival rates, cancer recurrence and consumption of soy. In this study, more than 5,000 breast cancer survivors (treated by surgery) were followed for 60 months. During this time, there were 444 deaths and 534 recurrences. The patients’ consumption of soy or soy products was also closely recorded.
Interestingly, those who had the highest daily intake of soy had about a 30 percent reduction in death and recurrence of cancer when compared to those who ate little soy. These results were also the same for those who were estrogen receptor negative. The use of the drug tamoxifen (which blocks the estrogen receptor) did not change the results. The findings of the study were “- soy food consumption was significantly associated with decreased risk of death and recurrence (of breast cancer).”
As positive as these results seem to be, I advise caution. One study, positive or negative, is not absolute proof. However, most dietary soy products (except soy beans) do not actually contain high concentrations of phytoestrogens. Flax seed can contain three times more phytoestrogens than soybeans. Multigrain bread and sesame seeds also have a substantial amount of phytoestrogens. So, is soy safe? As a food, most of the data says yes. Concentrated soy capsules – we just do not know.
For those with breast cancer, a healthy diet is essential and that includes foods that are high in phytoestrogens. I believe that future research will conclusively show that a diet rich in phytoestrogen-containing foods lowers the risk of breast cancer recurrence as well as improves survival.
Posted January 14, 2010.
