Validation of a phytoestrogen food frequency questionnaire with urinary concentrations of isoflavones and lignan metabolites in premenopausal women.

OBJECTIVE

The purpose of this study was to examine the association between dietary intake of phytoestrogens estimated by a food frequency questionnaire (FFQ) with urinary metabolites.

METHODS

Participants were 26 premenopausal, Caucasian women aged 25 to 42 years. Dietary intake of isoflavones (genistein and daidzein) and lignans (secoisolariciresinol and matairesinol) were estimated by a 53-item interviewer-administered FFQ on two occasions, reflecting 'habitual' (previous 2 months) and 'recent' (previous 2 days) dietary intake. Isoflavone (genistein, daidzein) and lignan (enterolactone, enterodiol and secoisolariciresinol) concentrations were measured in 24-hour urine samples by gas chromatography-mass spectrometry. Correlations between FFQ (habitual and recent, separately) and urinary metabolite values were assessed using Spearman correlation coefficients.

RESULTS

Mean habitual isoflavone and lignan intakes were 13.7 mg/day and 13.8 mg/day, respectively. Mean urinary concentrations of isoflavones and lignans were 17.4 micromol/day and 20.6 micromol/day, respectively. Recent and habitual isoflavone intakes were correlated with urinary excretion of metabolites (r = 0.64, p < 0.001 and r = 0.54, p = 0.004, respectively). Urinary excretion of lignans was also modestly correlated with recent and habitual lignan intakes (r = 0.46, p = 0.02 and r = 0.40, p = 0.05, respectively).

CONCLUSIONS

Our results support the use of this FFQ as a measure of dietary isoflavone and lignan intake in epidemiological studies.