The largest study so far of how the traditional soy-rich Japanese diet impacts development of prostate cancer in Japanese men has come to a seemingly contradictory conclusion: intake of isoflavone chemicals, derived largely from soy foods, decreased the risk of localized prostate cancer but increased the risk of advanced prostate cancer.

The prospective study of 43,509 men, published in the March issue of Cancer Epidemiology, Biomarkers & Prevention, suggests that the effects of isoflavones on prostate cancer development may differ according to disease stage, say researchers at the National Cancer Center in Japan.

Isoflavones may delay the progression of latent prostate cancer only, the researchers suggest. Once tumors lose estrogen-receptor beta expression and become aggressive, isoflavones may