Soy and its components, particularly isoflavones such as genistein and daidzein, have been investigated for their potential role in supporting or treating Benign Prostatic Hyperplasia (BPH). The rationale is partly based on epidemiological observations that populations consuming soy-rich diets (e.g., in East Asia) have lower rates of prostate enlargement and related symptoms compared to Western populations. Isoflavones are phytoestrogens, which can weakly bind to estrogen receptors and may modulate hormonal pathways involved in prostate tissue growth.

However, clinical evidence is limited and mixed. Some small clinical trials and animal studies suggest soy isoflavones might modestly improve urinary symptoms or slow prostate growth, possibly due to anti-inflammatory or hormone-modulating effects. For example, a few randomized controlled trials (RCTs) have reported slight improvements in International Prostate Symptom Scores (IPSS) and prostate volume, but these effects tend to be small and inconsistently reproduced. Systematic reviews and meta-analyses generally conclude that, while soy isoflavones appear safe, the evidence for meaningful benefit in BPH management is weak or inconclusive.

In summary, the use of soy for BPH is supported by some scientific rationale and preliminary data, but high-quality, large-scale clinical trials demonstrating clear clinical benefit are lacking. Thus, the evidence supporting soy for BPH can be rated as low (2/5).