Recent articles have discussed the benefits of eating soy products to reduce the risk of breast cancer, but experts say the effects are still unknown and that consuming soy may actually increase breast cancer risk for some women. A new review says phytoestrogens may have both a protective role and a stimulatory role in breast cancer cell growth depending on several factors, including at what age they’re consumed and whether they’re consumed as food or as supplement. The report appears in the September/October 2007 issue of CA: A Cancer Journal for Clinicians, a peer-reviewed journal of the American Cancer Society.
The phytoestrogens in soy have been studied even more since studies suggest that women from countries with high consumption of soy, which have significant levels of phytoestrogens, have less risk of breast cancer. Studies have shown Asian women have a breast cancer rate one-fifth that of Western women, and some research suggests the lower rates are linked to consumption of soy, a staple of the Asian diet. In addition to their potential role in reducing the risk of breast cancer, phytoestrogens have also begun to be used by many women with a history of breast cancer in the belief that they are a safer way to treat menopausal symptoms.
The effects of phytoestrogens on a woman's body are not fully understood. Soy is high in phytoestrogens, which are natural chemicals found in plants that act like weak forms of the estrogens naturally produced in a woman's body. Soy is especially high in the phytoestrogen isoflavone. It is believed that phytoestrogens compete with estrogen to fit into estrogen receptor sites in different parts of the body, including breast tissue. Because estrogen stimulates cell reproduction, it may be that the more exposure a women has to estrogen, the greater her breast cancer risk. In premenopausal women, phytoestrogens may have an estrogen-reducing effect because they attach to estrogen receptor sites, thus tricking the body into producing less estrogen.
The effect of phytoestrogens is less clearly understood in postmenopausal women, whose estrogen levels are naturally lowered. Although there is some evidence to suggest consumption of soy reduces breast cancer risk in premenopausal women, there is no evidence that consumption of soy reduces postmenopausal breast cancer risk.
Unfortunately, there is no compelling evidence that phytoestrogens help menopausal symptoms, and given potential concerns for stimulating breast cancer cell growth, it should not be recommended for use to treat these symptoms in post-menopausal women. In particular, women who are taking tamoxifen should be cautioned against the use of soy supplements and purified products. Although the link between diet and breast cancer is not yet clearly understood, specialists agree there are health benefits associated with consuming a diet rich in naturally occurring plant chemicals found in soy products such as tofu and in the fiber of whole grains, berries, fruits, vegetables, and flaxseed. Whether and how such a diet contributes to cancer prevention is not clearly answered and more studies need to be done in the future.
Rebecca
