Phytoestrogens are plant-derived compounds structurally and functionally similar to estrogen. They are found in foods such as soy, flaxseed, and red clover. The rationale for using phytoestrogens to support or treat premenstrual syndrome (PMS) lies in their ability to modulate estrogenic activity in the body. Since PMS symptoms are thought to be related, in part, to fluctuations and imbalances in sex hormones (notably estrogen and progesterone), phytoestrogens may theoretically help normalize hormone levels and reduce symptom severity.

Scientifically, evidence for the efficacy of phytoestrogens in treating PMS is limited and mixed. Some small clinical trials have explored the effects of soy isoflavones (a type of phytoestrogen) on PMS symptoms, with a few studies reporting modest benefits for mood swings, breast tenderness, and bloating. However, the quality of these studies is generally low, with small sample sizes and methodological limitations. Systematic reviews and meta-analyses typically conclude that while there is some biological plausibility, robust evidence supporting phytoestrogen supplementation for PMS is lacking. There is insufficient data to recommend phytoestrogens as a first-line or definitive treatment for PMS.

In summary, while there is some scientific investigation into phytoestrogens for PMS and a biological rationale, the quality and quantity of evidence are not strong, and further research is necessary to determine their true efficacy.