Urinary isoflavone excretion as a compliance measure in a soy intervention among young girls: A pilot study

Abstract

Objective: To investigate the compliance of young girls with a soy intervention. Design: An 8-week dietary intervention and urine sample collection. Setting: Free-living girls. Subjects: A convenience sample of 8- to 14-y-old girls (20 started and 17 finished the study) recruited through flyers distributed to staff members and previous study participants. Intervention: The girls consumed one daily serving of soymilk, soy nuts, or tofu, completed 3-day food records, kept daily soy intake logs, and collected weekly urine samples. Main outcome measures: Compliance with the intervention was evaluated by daily soy intake logs, 3-day food records analyzed by the center's Food Composition and Food Groups Servings Databases, and weekly urinary isoflavone excretion using high-pressure liquid chromatography. The statistical analysis included paired t-tests, analysis of variance, and Spearman's rank-order correlation coefficients. Results: Daily soy intake logs indicated a mean intake of 6.28 servings out of a maximum of 7.0 servings per week. The food records revealed a six-fold increase in isoflavone intake during the study period (P < 0.01) which was confirmed by an increase in urinary isoflavone excretion of similar magnitude (23.3-142.1 nmol/mg creatinine, P = 0.02). Conclusions: This study demonstrated the ability of young girls to consume one daily soy serving and the usefulness of urinary isoflavones as a primary compliance measure. The high urinary isoflavone excretion levels detected in girls as compared to adult women suggest less intestinal degradation and/or greater absorption of isoflavones in nonadult populations. This finding requires further investigations into the pharmacokinetics of isoflavones. © 2005 Nature Publishing Group All rights reserved.