A Six-Month Randomized Controlled Trial of Whole Soy and Isoflavones Daidzein on Body Composition in Equol-Producing Postmenopausal Women with Prehypertension

Six-month randomized controlled trial with a 1:1:1 allocation to whole soy, daidzein, or placebo. Participants were Hong Kong Chinese postmenopausal women aged 48-65 years who were equol producers and had prehypertension.

Whole soy was provided as 40 g soy flour daily by oral ingestion as a beverage powder mixed with 300 mL water or beverages for 6 months. The daidzein regimen provided 63 mg daidzein daily plus 40 g low-fat milk powder, also taken orally for 6 months; the comparator was an isocaloric milk placebo.

Whole soy and purified daidzein did not improve body weight or body composition compared with placebo. At 6 months, body weight change was 0.20 ± 1.78 kg with whole soy, 0.59 ± 3.35 kg with daidzein, and -0.20 ± 1.53 kg with placebo, with no significant between-group differences by ANOVA. BMI, waist and hip circumference, waist-to-hip ratio, body fat percentage, fat mass, and free fat mass also showed no significant differences among groups. The authors concluded that six months of whole soy or daidzein did not produce meaningful anthropometric or body composition benefits in this population.

The trial had a relatively narrow population: equol-producing Hong Kong Chinese postmenopausal women with prehypertension, limiting generalizability. Body composition outcomes were assessed over only 6 months, and physical activity was not well characterized, which may reduce sensitivity to detect modest effects. Dietary soy intake was intentionally restricted, adding a controlled but artificial context.