Randomized controlled trial of whole soy and isoflavone daidzein on menopausal symptoms in equol-producing Chinese postmenopausal women.

OBJECTIVE: Dietary supplements containing soy or isoflavones are widely used as alternatives to hormone therapy. However, their efficacy is still inconclusive, and limited data on equol producers are available. The aim of this study was to examine the effect of whole soy (soy flour) or purified daidzein (one major soy isoflavone and the precursor of equol) on menopausal symptoms in equol-producing postmenopausal women, a population most likely to benefit from soy intervention.

METHODS: This is a 6-month parallel-group, double-blind, randomized, placebo-controlled trial. Two hundred seventy equol-producing prehypertensive Chinese postmenopausal women were randomized to one of three treatment groups: 40 g of soy flour (whole soy group), 40 g of low-fat milk powder + 63 mg of daidzein (daidzein group), or 40 g of low-fat milk powder (placebo group) daily, each given as a solid beverage for 6 months. Changes in menopausal symptoms were assessed by a validated and structured symptom checklist at baseline and 6 months.

RESULTS: Two hundred fifty-three participants completed the study according to protocol. Urinary isoflavones indicated good compliance with the interventions. Baseline menopausal symptoms were comparable among the three study groups. Intention-to-treat analysis indicated that there was no significant difference in the 6-month changes or percent changes in the total number of menopausal symptoms, in the five dimensions of symptoms, and in the frequencies of individual symptoms among the three treatment groups.

CONCLUSIONS: Whole soy and purified daidzein have no significant effect on alleviation of menopausal symptoms among equol-producing postmenopausal women with prehypertension.