title: Validation of a soy food frequency questionnaire with plasma concentrations of isoflavones in US adults.
abstract: 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.
authors.affiliation: Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
authors.forename: Cara L
authors.initials: CL
authors.lastname: Frankenfeld
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Patterson
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Kalhorn
authors.forename: Heather E
authors.initials: HE
authors.lastname: Skor
authors.forename: William N
authors.initials: WN
authors.lastname: Howald
authors.forename: Johanna W
authors.initials: JW
authors.lastname: Lampe
mesh_terms: 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
chemical_list: D007529:Isoflavones; C004742:daidzein; D019833:Genistein