Soyfoods & Prostate Cancer
As in the case of breast cancer, rates of prostate cancer are relatively low in soyfood-consuming countries. There is also evidence that in these countries, prostate cancer doesn’t progress as readily from the beginning stages of the disease, which is not life-threatening, to the stage at which the disease is capable of spreading or metastasizing to other tissues. At that point, prostate cancer is quite lethal. Since prostate tumors are generally slow-growing and are typically diagnosed at a relatively late age, modestly delaying the development of the disease and/or slowing the growth of prostate tumors can dramatically reduce prostate cancer mortality. In other words, if the progress of the disease can be sufficiently slowed, men will die with their tumor rather than because of their tumor.
In a recent comprehensive statistical analysis of epidemiologic studies, researchers from the US Department of Agriculture and Washington University in St Louis found that among studies involving Asian men, individuals who consumed the most soy were almost 50% less likely to have prostate cancer than those who consumed relatively little soy. This suggested protective effect of soyfood intake is generally consistent with results from animal studies.
In addition to possibly preventing the development of prostate cancer, soy consumption will also help prevent its metastasis, according to both animal and human evidence. For example, a recent study published in the Journal of the National Cancer Institute reported that the level of an enzyme that allows cells to invade tissues was markedly reduced in prostate cancer patients given the soybean isoflavone genistein. In a separate animal study, adding isoflavones to the diet in mice was found to inhibit prostate tumor metastasis by 96%.19 Finally, in men with prostate cancer whose treatment has been unsuccessful, preliminary evidence suggests that soy isoflavones are of benefit. Some studies show that isoflavones slow the rise in prostate specific antigen (PSA) levels.20 PSA is protein produced by the prostate that can be measured in the blood, and is used as a marker of prostate cancer.
