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.


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


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


METHODS
Isoflavone intake was determined from responses to a 40-item soy FFQ and from tofu and soymilk intake assessed as part of a comprehensive FFQ used for the Women's Health Initiative (WHI FFQ). Isoflavone concentrations in fasting blood samples were determined by liquid chromatography-mass spectrometry.


METHODS
Correlation coefficients were calculated for: a) isoflavone intake assessed by the soy FFQ and the WHI FFQ, b) intake assessed by the soy FFQ and plasma isoflavone concentrations, and c) intake assessed by the WHI FFQ and plasma isoflavone concentrations.


RESULTS
Isoflavone intake was highly correlated between the soy FFQ and the WHI FFQ (r = 0.84). Genistein and daidzein intakes determined by the soy FFQ were significantly correlated with plasma concentrations (r = 0.53 and 0.45, respectively). Isoflavone intake assessed from the WHI FFQ was also correlated with plasma concentration (r = 0.46 and 0.45). Soymilk and tofu were the two major contributors to isoflavone intake (38.6%).


CONCLUSIONS
A soy-specific, 40-item FFQ assessed isoflavone intake with good validity. Isoflavone intake assessed by the WHI FFQ (tofu and soymilk) had lower correlations with plasma concentrations compared with the soy FFQ. Nonetheless, assessment of the two foods is a reasonably good marker for soy food consumption in this sample.
Frankenfeld
Cara L
CL
Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
Patterson
Ruth E
RE
Kalhorn
Thomas F
TF
Skor
Heather E
HE
Howald
William N
WN
Lampe
Johanna W
JW
D000328:Adult; D003430:Cross-Sectional Studies; D004034:Diet Surveys; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D019833:Genistein / Q000008:administration & dosage / Q000097:blood*; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage / Q000097:blood*; D008297:Male; D015203:Reproducibility of Results; D013025:Glycine max / Q000737:chemistry; D011795:Surveys and Questionnaires / Q000592:standards*; D014861:Washington
D007529:Isoflavones; C004742:daidzein; D019833:Genistein