Urinary equol excretion in relation to 2-hydroxyestrone and 16alpha-hydroxyestrone concentrations: an observational study of young to middle-aged women.

Approximately one-third to one-half of individuals harbor the colonic bacteria that are capable of metabolizing the soy isoflavone daidzein to equol. Results of prior studies suggest beneficial effects of producing equol in relation to breast cancer risk, potentially through effects on endogenous hormones. High urinary excretion of 2-hydroxyestrone (2-OH E(1)) relative to 16alpha-hydroxyestrone (16alpha-OH E(1)) has been associated with a reduced risk of breast cancer.

Validation of a soy food-frequency questionnaire and evaluation of correlates of plasma isoflavone concentrations in postmenopausal women.

Background: Soy foods may have various health benefits, but little is known about the patterns and correlates of soy consumption among postmenopausal women in the United States.

Objective: We assessed the reliability and validity of a soy food-frequency questionnaire (FFQ) and examined demographic, lifestyle, and dietary correlates of plasma isoflavone concentrations in postmenopausal women.

Design: In this cross-sectional study, soy isoflavone intake and plasma isoflavone concentration were analyzed in 96 postmenopausal women aged 50-79 y; the data were obtained at 2 visits that were 1 wk apart.

Validation of a soy food frequency questionnaire with plasma concentrations of isoflavones in US adults.

Objective: To validate assessment of soy intake using food frequency questionnaires (FFQs) compared with plasma isoflavone (genistein and daidzein) concentrations.

Design: Cross-sectional analysis of soy isoflavone intake and plasma analysis of isoflavones.

Subjects: 77 men and women, age range 20 to 40 years, recruited from the Seattle metropolitan area.

Overnight urinary isoflavone excretion in a population of women living in the United States, and its relationship to isoflavone intake.

Dietary isoflavones are biologically active in humans, but few observational data exist on the relationship between isoflavone intake and excretion in Western populations. We examined associations between self-reported soy intakes and overnight urinary isoflavone excretion in a population-based sample of western Washington State women, and we investigated the usefulness of one versus two overnight urine samples, collected 48 h apart, as a biomarker of intake. Isoflavones (genistein, daidzein, O-desmethylangolensin, and equol) were measured in two overnight urine collections from 363 women recruited from a health maintenance organization.

Dietary determinants of plasma enterolactone.

Enterolactone is a lignan produced by fermentation of dietary precursors in the human gut. Because lignan precursors are uniquely found in plant foods, plasma enterolactone concentration may serve as a biological marker of plant food consumption. This cross-sectional study examined associations of dietary intake with plasma enterolactone concentration.