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.


METHODS
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. Intake was determined with a 20-item soy FFQ and a comprehensive FFQ that included questions about tofu and soymilk. Fasting plasma daidzein and genistein concentrations were determined with liquid chromatography-mass spectrometry.


RESULTS
Intraclass correlations between week 1 and week 2 values were >0.98 for both the soy and comprehensive FFQs. Median reported isoflavone intake was <2 mg/d. Pearson's product-moment correlation coefficients relating isoflavone intakes with plasma isoflavone concentrations ranged from 0.35 to 0.43. Plasma isoflavone concentrations were positively associated with age, fiber consumption, servings of fruit and vegetables, and dietary supplement use and were inversely associated with caffeine consumption; no associations with body mass index, education, dietary beliefs, activity level, alcohol intake, or fat intake were observed.


CONCLUSIONS
Within a population with low soy consumption, the soy FFQ and comprehensive FFQ showed good reliability and moderate validity. Associations of plasma isoflavone concentrations with other dietary behaviors suggest that these compounds may serve as biomarkers of health behaviors in populations with low soy consumption.
Frankenfeld
Cara L
CL
Fred Hutchinson Cancer Research Center, Cancer Prevention Research Program and the Department of Epidemiology, University of Washington, Seattle, 98109-1024, USA.
Patterson
Ruth E
RE
Horner
Neilann K
NK
Neuhouser
Marian L
ML
Skor
Heather E
HE
Kalhorn
Thomas F
TF
Howald
William N
WN
Lampe
Johanna W
JW
D000368:Aged; D015415:Biomarkers / Q000097:blood; D003430:Cross-Sectional Studies; D004043:Dietary Fiber / Q000008:administration & dosage; D005247:Feeding Behavior; D005260:Female; D005638:Fruit; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D019833:Genistein / Q000097:blood; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage / Q000097:blood*; D008019:Life Style; D008875:Middle Aged; D017698:Postmenopause; D015203:Reproducibility of Results; D013025:Glycine max; D011795:Surveys and Questionnaires / Q000592:standards*; D014675:Vegetables
D015415:Biomarkers; D004043:Dietary Fiber; D007529:Isoflavones; C004742:daidzein; D019833:Genistein