Phytoestrogens are plant-derived compounds that have structural similarity to endogenous estrogens and can exert weak estrogenic or anti-estrogenic effects. Their use in the context of PMS Type S (premenstrual syndrome, Salt-retaining type) is primarily based on their potential to modulate estrogen activity, as Type S PMS is often theorized to be related to fluctuations or excesses in estrogen relative to progesterone. Some small studies and mechanistic research suggest that phytoestrogens, such as those found in soy (isoflavones), may help balance estrogenic activity and alleviate certain PMS symptoms, including bloating and breast tenderness—symptoms commonly associated with PMS Type S.

However, clinical evidence is limited and results are inconsistent. A few randomized controlled trials have explored the effect of phytoestrogen-rich diets or supplements on PMS symptoms, with some reporting modest improvements and others showing no significant benefit over placebo. Most studies are small in size and short in duration, and often do not specifically focus on PMS Type S. Systematic reviews typically conclude that while there is a plausible biological mechanism, the quality and quantity of evidence is insufficient to make strong recommendations.

In summary, the use of phytoestrogens for PMS Type S has some scientific rationale and preliminary support, but robust, high-quality evidence is lacking. The rating reflects the current state of research: promising, but not definitive.