Relationship between serum isoflavone concentrations and frequency of soybean products consumption in patients with prostate cancer

Dietary consumption of high concentrations of soybean products has been suggested to reduce the risk for prostate cancer (PCa). We conducted a survey using patients with PCa to assess the relationship between serum concentrations of isoflavone aglycones and frequency of soybean products consumption in patients with PCa. We measured the serum concentrations of daidzein, genistein, glycitein, and equol in 99 PCa patients, in addition to conducting a survey using a self administrated questionnaire that included the frequencies of various food item consumptions. If serum concentrations of equol were at a value less than 0.5 ng/mL, they were classified as an equol non producer, and the other patients were classified as equol producers. As a result, serum concentrations of daidzein, genistein, and glycitein were found to be significantly correlated to each other (P<0.001). The frequency of tofu (soybean curd) consumption was significantly correlated with the serum concentration of daidzein (P<0.05). Likewise, the frequency of natto (fermented soybean) consumption was significantly correlated with the serum concentrations of daidzein, genistein, and glycitein (P<0.01). In the study there were 40 equol producers and 59 equol non producers, but none of the food items were significantly different between the equol producers and the equol non producers. We have a plan to perform a similar survey for population based controls in the future. Comparisons between the data of the PCa patients and the controls would give us more information about the role of isoflavones and equol production in regard to the risk of PCa.