A Japanese study published in Cancer Epidemiology Biomarkers & Prevention found a correlation between increased intake of soy isoflavones and decreased risk of localized prostate cancer. The same study found, however, that a high intake of these compounds correlated with more severe cases of advanced prostate cancer.
• Isoflavones are plant compounds that act as antioxidants and estrogen mimics in the human body. Animal studies suggest that soy isoflavones may help prevent prostate cancer, but previous epidemiological studies on humans have had mixed and inconclusive results.
• In the current study of 32,509 Japanese men between the ages of 45 and 74, consumption of foods high in soy isoflavones was not correlated with a reduced risk of prostate cancer overall. It did correlate, however, with a reduced risk of localized prostate cancer. This correlation was strongest among men 60 or older.
• Localized prostate cancer is a cancer found entirely within the prostate that has not spread to other parts of the body.
• The causal relationship leading to the reduced cancer risk is not known. While the decreased risk may be caused by the isoflavones, it might be caused by other factors related to soy intake -- for example, a correlation between high soy intake and lowered consumption of meat and dairy.
• Consumers looking for foods to prevent prostate cancer can do much better than soy products. Whole tomatoes, pomegranates, green tea and even common minerals like zinc offer very effective preventive medicine against cancers of the prostate.
• I do not recommend soy products unless they are fair trade, certified organic, non-GMO fermented soy products such as tofu. Most soy bought in the United States, including soy protein, is genetically modified soy.