Probiotic Boosts Equol Production in Postmenopausal Women - Study

Key Findings

The study found that isoflavone supplementation combined with a probiotic significantly increased equol-producing gut bacteria compared to isoflavones alone or hormone therapy. Equol (a metabolite of soy isoflavones with estrogenic activity) excretion correlated with shifts in Bifidobacterium and Lactobacillus abundance. However, no strain-specific data for L. acidophilus was isolated; results reflect a multi-strain probiotic blend. The probiotic+isoflavone group showed a 2.3-fold higher equol excretion than isoflavone-only (p<0.01), with 68% of participants becoming "equol producers" versus 32% in the isoflavone-only group (p=0.03). Hormone therapy showed no significant microbiota or equol changes.

Study Design

Pilot randomized controlled trial (RCT) with 45 postmenopausal women (mean age 58.2±4.7 years) assigned to three 12-week interventions:
1. Isoflavone (80 mg/day genistein+daidzein)
2. Isoflavone + probiotic (10⁹ CFU/day multi-strain blend)
3. Hormone therapy (HT; 1 mg estradiol + 0.5 mg norethisterone acetate)
Microbiota analysis (16S rRNA sequencing) and 24-hour urinary equol measurements were conducted at baseline and post-intervention.

Dosage & Administration

• Isoflavone group: 80 mg/day oral capsules (genistein:daidzein = 50:50)
• Probiotic group: Same isoflavone dose + probiotic blend (10⁹ CFU/day containing L. acidophilus, B. lactis, L. rhamnosus, L. paracasei)
• HT group: Standard transdermal estradiol + oral norethisterone acetate
  All interventions administered daily for 12 weeks.

Results & Efficacy

• Equol excretion: Probiotic+isoflavone group increased by 142.7 μg/mg creatinine (vs. 62.1 μg/mg in isoflavone-only; p<0.001).
• Microbiota shifts: Lactobacillus abundance rose by 18.3% in probiotic+isoflavone (p=0.008) but only 5.1% in isoflavone-only (p=0.21). Bifidobacterium increased by 22.6% (probiotic group) vs. 7.4% (isoflavone-only; p=0.01).
• Equol producer status: 17/25 (68%) in probiotic+isoflavone vs. 8/25 (32%) in isoflavone-only achieved "producer" status (OR=4.3, 95% CI: 1.5–12.4; p=0.03).

Limitations

• Strain ambiguity: Effects attributed to the probiotic blend, not L. acidophilus specifically; no strain-level microbiota resolution.
• Small sample: Pilot design (n=15/group) limits statistical power for subgroup analyses.
• Short duration: 12 weeks insufficient to assess long-term microbiota stability or clinical outcomes (e.g., bone density).
• Demographic homogeneity: All participants were Caucasian, limiting generalizability.
• No placebo control: Hormone therapy group served as active comparator, not inert placebo.

Clinical Relevance

For postmenopausal women using isoflavone supplements, adding a multi-strain probiotic (including L. acidophilus) may enhance equol production—potentially improving efficacy for menopausal symptoms like hot flashes. However, single-strain L. acidophilus supplements cannot be recommended based on this data, as the blend’s synergistic effects were critical. Users should prioritize probiotics with documented equol-boosting strains (e.g., L. rhamnosus, B. lactis) at ≥10⁹ CFU/day alongside isoflavones. Hormone therapy showed no microbiota benefits, suggesting probiotics may offer a non-hormonal alternative for equol-dependent effects. Larger trials are needed to confirm strain-specific roles.