Background: Our previous case-control study revealed that Japanese living in Japan and Koreans living in Korea can be divided into equol producers who have an ability to metabolize daidzein to equol and non-producers, and that the incidence of prostate cancer is higher in the latter group. In the present study, we examined relationships between type of food intake and the capacity for equol production in Japanese subjects. Methods: The subjects were the individuals analyzed for the ability to produce equol in our previous study and newly registered cases. From December 2000 to December 2002, 276 hospitalized patients were interviewed face-toface and blood samples were collected before breakfast. These included 122 patients with prostate cancer and 154 age-matched controls. Result: The frequency of equol producers (0.5 ng/ml or more) among cases and controls was 29% and 45%, respectively (p = 0.004). The consumption of soybeans and green tea were significantly higher in equol producers than in the non-producers (p<0.05). By contrast, the consumption of selenium and fiber was significantly lower in equol producers (p<0.05). Conclusion: Our results suggest that higher consumption of soybean and green tea are strongly related to the establishment of a capacity for equol production.