According to the National Cancer Institute, 207,090 American women received a diagnosis of breast cancer in 2010. Ongoing causative studies consider diet a possible factor. Prompted by the low incidence of breast cancer in Asian countries, researchers honed in on the diet of these cultures and attributed the high breast cancer rate in U.S. woman to a lack of the dietary soy that their Asian counterparts consume. However, studies show mixed results and create many unanswered questions.
Soy
The soy plant contains substances with estrogen-like properties called phytoestrogens. Three hundred other plants also contain phytoestrogens, but not at the concentrated levels of soy. Soy is the only plant food that has a complete protein, akin to that found in animal meats. Some products of the soy plant include tofu, tempeh, soy milk, miso and edamame, a green version of the soybean. In the body, soy phytoestrogens mimic estrogen. Small amounts of phytoestrogens act like estrogen, but in high amounts phytoestrogens can block estrogen. Theoretically, soy should block estrogen receptors in breast cancers that are estrogen-receptive. However, results of studies about these effects conflict with each other, according to Cornell University.
Inadequate Studies
Studies linking soy to breast cancer have had conflicting results. Cornell University reports that the shortcomings of such studies include too small sample sizes; too few studies done; a comparison between Asian women and American women that does not take other environmental factors into consideration; and a focus on general diet rather than a detailed study of phytoestrogens. In animal studies, fewer mammary tumors occurred in some but not all subjects on a high soy diet. In human studies, age of the subjects also affected outcomes. For instance, a high soy diet given to prepubescent girls prior to breast development appeared to inhibit the occurrence of breast cancer later in life, reports Cornell University
Results by Stages
In breast cancer, progressive stages reflect tumor size, location and spread. Stage 0 indicates the existence of abnormal, non-invasive cells. Stage I indicates a cancerous tumor that may have spread to surrounding tissue. Stage II signifies a malignant tumor of 2 centimeters or less without spread to the lymph nodes. The stages continue to stage IV and become increasingly more life-threatening, according to the National Cancer Institute. The results of a study, released by the State University of New York at Buffalo found that newly diagnosed women on a high soy diet showed a 30 percent decreased risk of having stage 0 carcinoma and a 60 percent decreased risk of developing a stage l tumor. Further, the results demonstrated a 60 percent lowered risk of developing stage II breast cancer.
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Anne Weaver, the epidemiologist who conducted the study at the University at Buffalo, admitted further studies should confirm the results. The major flaw to her study was a lack of controls over how much plant hormone came from other sources besides the soy plant, which rendered the findings inconclusive. Currently, the recommendation for consuming a high soy diet by breast cancer patients remains in limbo. According to Cornell University, the safety and effectiveness of soy in controlling breast cancer's advancement is still largely unproven.
References
- National Cancer Institute: Cancer Facts, January 14, 2004
- State University of New York at Buffalo; Soy Isoflavones Decrease Risk of Invasive Breast Cancer, Large Breast Tumors, Study Shows; Nov. 30, 2010
- Cornell University Program on Breast Cancer and Environmental Risk Factors; Phytoestrogens and Breast Cancer; July 2001
- National Cancer Institute: Breast Cancer Treatment, 2010
