Sunday Dec 21, 2008 (foodconsumer.org) -- Eating soy products may help men prevent the development of prostate cancer, a new Japanese study published in the Dec 2008 issue of Journal of clinical Oncology suggests.

The study led by Kurahashi N and colleagues of the National Cancer Center in Tokyo Japan found that people who had highest plasma levels of genistein and equol were at a significantly reduced risk of localized prostate cancer than those with lowest levels.

Equol is an isoflavandiol metabolized from daidzein, a type of isoflavone, by bacterial flora in the intestines. Genistein is one of several known isoflavones found in soybeans, according to wikipedia.

The incidence of prostate cancer in Japan is much lower in Japan than the West prompted the researchers to examine an association between prostate cancer risk and soy consumption, which common in Japan.

For the study, Kurahashi and colleagues followed 14,203 men aged 40 to 69 years for 12.8 years between 1990 and 2005. At baseline, participants’ dietary patterns were surveyed using a questionnaire and blood samples were tested.   The study compared 201 prostate cancer cases recorded during the follow-up with 402 men without the disease.

They found the plasma genistein level tended to be inversely associated with the risk of total prostate cancer.  

Daidzein did not show the inverse association with the cancer risk, but those in the quintile of highest levels of plasma equol, a metabolite of daidzein were 40 percent less likely to acquire prostate cancer than those who were in the lowest levels of plasma equol.

The associations of plasma levels of genistein and equol with localized prostate cancer were even much stronger.   Those who had the highest levels of genistein and equol were 46 and 57 percent less likely to contract the disease, respectively.

The researchers suggest that isoflavones may prevent the development of prostate cancer.