title: Validation of a food frequency questionnaire for assessing dietary soy isoflavone intake among midlife Chinese women in Hong Kong.
abstract: Substantial evidence suggests that soy isoflavones may protect against certain chronic diseases. This study aims to assess the reproducibility and validity of a 47-item semiquantitative soy FFQ (SFFQ) designed to measure the usual intake of soy isoflavones among 145 Chinese mid-life women in Hong Kong. Reproducibility of the SFFQ was assessed by the stability of dietary intake obtained at baseline (SFFQ0) and at 13-mo follow-up (SFFQ1). Relative validity was measured by comparing data collected from SFFQ1 with those derived from 23-d, 24-h dietary recalls (DR) collected during the same 1-y validation period. Isoflavone intake was calculated using analytical values from the Chinese University of Hong Kong Soy Isoflavone Database. A total of 3,217 DR were successfully obtained. The median (interquartile range) absolute intake estimated by the SFFQ1 was 0.91 (-2.7 to 6.8) mg aglucon equivalents/d higher than the 6.3 (3.7-10.7) mg aglucon equivalents/d measured by the DR (P < 0.0057; Wilcoxon's Signed Rank test). Bland-Altman analysis further demonstrated the presence of significant proportional bias between methods among Cantonese women with above-median intake (Spearman correlation coefficient; r = 0.44; P = 0.0005). Nonetheless, the intraclass and Pearson correlation coefficients, respectively, were 0.84 and 0.72 for non-Cantonese and 0.65 and 0.50 for Cantonese, showing moderate to good levels of reproducibility and validity of the SFFQ (difference between 2 intraclass correlation coefficients, P = 0.09; difference between 2 Pearson r, P = 0.16). The unadjusted and BMI-adjusted correlations were of similar magnitude. The SFFQ is a reasonably valid instrument for assessing dietary soy isoflavone exposure in Hong Kong Chinese mid-life women.
authors.affiliation: Department of Community and Family Medicine, Chinese University of Hong Kong, Hong Kong SAR. sieugaen2003@yahoo.com
authors.forename: Sieu G
authors.initials: SG
authors.lastname: Chan
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Ho
authors.forename: Nancy
authors.initials: N
authors.lastname: Kreiger
authors.forename: Gerarda
authors.initials: G
authors.lastname: Darlington
authors.forename: Edward M
authors.initials: EM
authors.lastname: Adlaf
authors.forename: Kam F
authors.initials: KF
authors.lastname: So
authors.forename: Portia Y Y
authors.initials: PY
authors.lastname: Chong
mesh_terms: D044466:Asian People; D004032:Diet; D004034:Diet Surveys; D005247:Feeding Behavior; D005260:Female; D006723:Hong Kong; D006801:Humans; D007529:Isoflavones; D008875:Middle Aged; D015203:Reproducibility of Results; D013025:Glycine max; D011795:Surveys and Questionnaires
chemical_list: D007529:Isoflavones