Phytoestrogens are plant-derived compounds structurally similar to human estrogen. They are found in foods such as soy, flaxseed, and some legumes. Their use in supporting or treating osteoporosis is primarily based on their ability to bind to estrogen receptors and exert weak estrogenic effects, which is relevant because postmenopausal osteoporosis is largely due to decreased estrogen levels.

Scientific studies, including randomized controlled trials and meta-analyses, have investigated the effects of phytoestrogens—especially soy isoflavones—on bone mineral density (BMD) and bone turnover markers in postmenopausal women. Some studies suggest modest improvements in BMD, particularly in the lumbar spine, and reductions in bone resorption markers. For example, a 2021 meta-analysis in Osteoporosis International concluded that soy isoflavone supplementation may have beneficial but limited effects on BMD in postmenopausal women. However, outcomes across studies are variable, with some showing no significant benefit.

While there is a plausible biological mechanism and some positive clinical data, the overall evidence is mixed and not as robust as for conventional osteoporosis treatments (such as bisphosphonates or hormone replacement therapy). Major guidelines do not currently recommend phytoestrogens as a primary treatment for osteoporosis, but they are sometimes considered as adjuncts or alternatives for women who cannot or prefer not to take conventional medications.