Much larger studies will be required to confirm the ability of soy products to reduce serum estrogen levels.

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Background: A self-administered quantitative food frequency questionnaire (ax) was developed for a population-based cohort study on cancer in Takayama, Japan.Methods: The ax was tested among 58 male and 59 female volunteers. Average daily nutrient intakes for the previous year calculated from the ax were compared with those from 3-day food records and four 24-h recalls. The ax was also validated among 37 volunteers by comparing the nutrient intakes calculated from the ax with 12 1-day food records during a year. We also calculated the intra-class correlation coefficients for various nutrients between the ax and the second ax administered by the same volunteers 1 year after the first survey.Results: Pearson correlation coefficients between total energy from the ax and 3-day records were 0.38 for men and 0.25 for women and those between the ax and 24-h recalls were 0.19 and -0.02 for men and women, respectively. Correlations between the several nutrients from the ax and 3-day records ranged from 0.2 to 0.5 for both men and women. These correlations after energy adjustment ranged from 0.2 to 0.6 for men and from 0.1 to 0.7 for women. In general, the correlations for various nutrients between the ax and 12 1-day records were higher than those described above. The intra-class correlation coefficients ranged from 0.46 to 0.78 in men and from 0.36 to 0.67, except for vitamin C in women. When the information on portion size was excluded, almost all of the above indices showed somewhat lower figures.Conclusion: These results suggest that our food frequency questionnaire with portion size information can be used to estimate nutrient intakes of each individual.

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The cross-sectional relationships of soy product intake and serum testosterone, estrone, estradiol, sex hormone-binding globulin, and dihydrotestosterone were examined in 69 Japanese men. Soy product intake was estimated from a semiquantitative food frequency questionnaire. Serum estradiol concentration was significantly inversely correlated with soy product intake (r = -0.32, p = 0.009), and serum estrone concentration was nonsignificantly inversely correlated with soy product intake (r = -0.24, p = 0.05) after controlling for age, body mass index, smoking status, and ethanol intake. Total and free testosterone concentrations were inversely correlated with soy product intake after controlling for the covariates, but these correlations were of border line significance (r = -0.25, p = 0.05 and r = -0.25, p = 0.06, respectively). Similar correlations were observed for these hormones with isoflavone intake from soy products. The data suggest that soy product intake may be associated with the endogenous hormone levels in Japanese men.