Two meta-analyses of randomized clinical trials, one considering 9 studies involving a total of 432 subjects, and the other reviewing 10 studies with a total of 608 subjects, have shown that consuming isoflavone-containing soy foods significantly inhibits bone loss and stimulates bone formation in menopausal women.
The first meta-analysis, published in the European Journal of Clinical Nutrition found that women whose daily diets provided soy isoflavones had much lower amounts of deoxypyridinoline (Dpyr, a bone resorption marker) in their urine, and much higher amounts of bone-specific alkaline phosphatase (BAP, a bone formation marker) in their blood. And these bone-protective effects occurred even if the women were consuming less than 90 mg of soy isoflavones per day or if the intervention lasted less than 12 weeks. (Ma DF, Qin LQ, et al.)
The second meta-analysis, published in Clinical Nutrition found that bone mineral density increased significantly (+27 mg/cm) in the spine of women whose diets provided soy isoflavones, even in amounts less than 90 mg/day, compared to those who did not. When more than 90 mg/day of isoflavones from soy foods was consumed for at least 6 months, improvements in spine bone mineral density became even more significant, increasing 28.5mg/cm. (Ma DF, Qin LQ, et al.)