Soy isoflavones, particularly genistein and daidzein, have been investigated for their potential role in supporting bone health and managing osteoporosis, especially in postmenopausal women. Scientific interest in soy stems from epidemiological observations that populations with high dietary soy intake tend to have lower rates of osteoporotic fractures. Isoflavones are classified as phytoestrogens, plant-derived compounds with weak estrogenic activity. Since estrogen deficiency after menopause accelerates bone loss, it was hypothesized that soy isoflavones might help mitigate this process.

Several randomized controlled trials and meta-analyses have explored the effects of soy or soy isoflavones on bone mineral density (BMD). Results are mixed: some studies report modest preservation of BMD or reductions in bone resorption markers, while others show little to no effect. A 2019 meta-analysis concluded that soy isoflavones may have a slight positive effect on BMD at the lumbar spine, but the clinical significance is questionable. Furthermore, the effect size is much smaller than that of established osteoporosis treatments (e.g., bisphosphonates).

In summary, while there is a plausible scientific rationale and some evidence supporting the use of soy isoflavones for bone health, the overall quality and consistency of evidence is moderate to low. Soy is not considered a primary or standalone therapy for osteoporosis, but may be viewed as a potentially beneficial dietary adjunct.