Soy isoflavones, known for their phytoestrogenic properties, are being explored as a natural option to alleviate the range of symptoms experienced during the premenstrual phase. In this study, researchers evaluated whether supplementation with isolated soy protein containing 68 mg/day of soy isoflavones could specifically reduce behavioral, somatic, and affective PMS symptoms compared to a milk protein placebo.
Protocols Studied in Research
Effect of Soy Isoflavones on Behavioral, Somatic, and Affective Symptoms in Women with Premenstrual Syndrome [1]
- Protocol: In this seven‑menstrual cycle, double‑blind, placebo‑controlled, crossover study, 23 women aged 18–35 years with prospectively confirmed PMS (BMI 19–30 kg/m²) were randomized to receive either isolated soy protein (ISP) containing 68 mg/day of soy isoflavones (including genistein, daidzein, and equol) or a milk protein placebo over two complete menstrual cycles. Urinary concentrations of isoflavones were measured from 24‑hour urine samples.
- Outcome: Compared to baseline, total and physical premenstrual symptom scores were significantly reduced after both active and placebo treatments, with no significant differences overall between the two. However, specific symptoms—including headache and breast tenderness—were reduced from baseline only after soy isoflavone treatment, while cramps and swelling were significantly lower with active treatment compared to placebo. Although genistein and daidzein levels increased with soy isoflavone consumption, equol production did not correlate with additional symptom reduction, suggesting that the beneficial effects may be mediated via non‑classical mechanisms.
Research Interpretation: Summary and Conclusion
While both the soy isoflavone treatment and placebo showed overall improvements in premenstrual symptoms from baseline, the soy group experienced additional benefits by specifically reducing headaches, breast tenderness, cramps, and swelling.
In simple terms, these targeted improvements suggest that soy isoflavones may act through non-traditional mechanisms, beyond simply mimicking estrogen, to alleviate certain PMS symptoms.
Publications
[1] Bryant M, Cassidy A, Hill C, Powell J, Talbot D, Dye L. Effect of consumption of soy isoflavones on behavioural, somatic and affective symptoms in women with premenstrual syndrome. Br J Nutr. 2005 May;93(5):731-9. doi: 10.1079/bjn20041396. PMID: 15975174.
