Development of a soy food frequency questionnaire to estimate isoflavone consumption in US adults.

OBJECTIVE: To develop a dietary assessment instrument to measure soy food consumption and isoflavone intake and test it for reliability.
DESIGN: A soy food frequency questionnaire, designed for use in this study, was administered twice to participants, separated by a 2-week interval. The questionnaire was tested for reproducibility of estimates of soy food consumption and isoflavone (genistein and daidzein) intake. SUBJECTS/
SETTING: A convenience sample of 51 faculty, staff, and students was recruited from a naturopathic university. STATISTICAL ANALYSES PERFORMED: Intraclass correlation coefficients were used to assess reproducibility of estimates of soy food intake and genistein and daidzein intake.
RESULTS: Correlation coefficients comparing mean soy food servings per month between the 2 administrations of the questionnaire ranged from 0.50 for soy yogurt to 0.89 for tempeh. Correlation coefficients for genistein and daidzein intake estimated by the 2 administrations of the questionnaire were the same: 0.89. Mean intake (+/- standard deviation) of genistein and daidzein was 7 +/- 10 and 4 +/- 6 mg/day, respectively. Fifteen soy foods contributed 95% of the total genistein and daidzein intake: tofu, soy yogurt, tempeh, soy milk, low-fat tofu, soy flour, miso, soy protein isolate, low-fat soy milk, veggie soy burger, textured vegetable protein, miso soup, cooked soybeans, soy hot dogs, and natto (fermented soy beans). APPLICATIONS: The soy food frequency questionnaire developed in this study provided highly reproducible estimates of soy food consumption and isoflavone intake. This instrument may be a useful tool in studies of the associations between isoflavone exposure and risk for chronic disease.