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.