Blood isoflavone levels during intake of a controlled hospital diet.

Isoflavones are reported to have an estrogenic activity to prevent prostate cancer. Therefore, it is necessary to analyze the factors influencing the absorption and metabolism of isoflavones using detailed and precise dietary information. We evaluated the relationship between the amount of intake of soybean isoflavones in the diet and its serum levels in 88 hospitalized patients (22 with prostate cancer, 66 without cancer) with a mean age of 67.0+/-9.3 y. The intake amount of genistein and daidzein was significantly lower in the hospital diet than that in the ordinary daily diet. The serum levels of isoflavones were related to the amount of intake consumed during the day before blood collection (r=0.27 for genistein, r= 0.33 for daidzein), but not to the last meal before blood collection. While little relationship was observed between the amount of intake and serum levels of isoflavones in the equol producers, a marked relationship was noted in the non-producers (r=0.52 for genistein, r=0.67 for daidzein). Blood isoflavone levels decreased when the duration of the hospitalization was longer than 1 wk. These observations indicate that the serum isoflavone levels are correlated with the amount of intake of isoflavones during the preceding 2 wk and serve as an effective biomarker in individuals during the intake of the hospital diet. Further investigations, including the mechanism of the metabolism on isoflavones, are necessary for the evaluation of the preventive effect of isoflavones.