Isoflavonoid content of Hong Kong soy foods.

Progress in understanding the effects of dietary soy isoflavones on chronic disease prevention in the Hong Kong Chinese population has been hampered by the lack of a comprehensive soy isoflavone database. In this study, we determined the concentrations and distribution of isoflavones in 47 foods included in a soy food frequency questionnaire by reverse-phase HPLC. Results indicated that most soy products contained isoflavones ranging from 1 mg of aglucon equivalents/100 g of wet weight (bean strip noodle and egg bean curd) to 80 mg of aglucon equivalents/100 g of wet weight (oyster sauce soybean and sweet bean curd sheet). Among our food groups, mean isoflavone concentrations were lowest in the soy milk group (9.99 mg of aglucon equivalents/100 g of wet weight) and highest in the bean curd skin group (40 mg of aglucon equivalents/100 g of wet weight). The conjugation patterns of isoflavones varied within and between food groups as influenced by the types of soybeans and the processing or cooking techniques used. The isoflavone concentrations reported herein will be useful for ascertaining the relationship between exposure to dietary soy isoflavones and health effects in the Chinese population.

Validation of a food frequency questionnaire for assessing dietary soy isoflavone intake among midlife Chinese women in Hong Kong.

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.