Study finds conflicting results on effects of soy in prostate cancer

Reported by Susan Aldridge, PhD, medical journalist

Soy foods seem to protect men from the spread of localized prostate cancer, but have the opposite effect in advanced disease.
The incidence of prostate cancer is lower in Asian countries, where the consumption of soy-based foods such as tofu and miso soup is common. Accordingly, researchers at the National Cancer Center in Japan have carried out an analysis of the evidence on soy and prostate cancer. This has come up with some seemingly contradictory data.

Men consuming high amounts of soy seem to be protected from the spread of local cancers. But once the cancer has become aggressive, soy actually seems to promote the progression of the disease. The researchers believe that localized and advanced prostate cancers are, in effect, different diseases which clearly respond in a different way to soy. Post-mortem data reveals there are no differences in the rates of latent and clinically insignificant prostate cancers among men from Asian and Western countries. This backs the theory that soy stops cancers spreading. The effect of soy on advanced cancers may work through its active components, the isoflavones, reducing the levels of testosterone in the blood. Men in Asian countries consume soy throughout their lives so it is not easy to say at what stage it is most protective. The researchers believe men should continue to consume soy with their diet, but should not take supplements, as this may cause some prostate cancers to progress.

Source
Cancer Epidemiology, Biomarkers & Prevention March 2007

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