The estrogen-like properties of soybean isoflavones led to speculation that soyfoods could help to reduce risk of developing osteoporosis. This speculation is supported by the results of prospective epidemiologic studies from Asia. However, clinical trials involving isoflavone supplements have produced very mixed results with some showing isoflavones reduce bone loss in postmenopausal women and other trials showing no benefits whatsoever.
The results from the most recent study to examine the skeletal benefits of isoflavones are solidly in support of their having beneficial effects. For this study Purdue University researchers utilized a novel methodology to study bone calcium retention. Postmenopausal women were first injected with 41Ca, a type of calcium which allows one to determine the amount of calcium being lost from the bones. In response to risedronate, which is bisphosphonate, a drug known to reduce bone loss, bone calcium retention was increased by about 15% over a 50-day period. When women were given soybean isoflavones, calcium retention was also significantly increased although by only about half as much as in response to the risedronate. The researchers thought the effect of isoflavones was very much clinically relevant concluding that these soybean constituents are effective bone-preserving agents for postmenopausal women.
The amount of isoflavones consumed daily by the women in this study was about 100 milligrams, the amount provided by about four servings of traditional soyfoods such as a cup of soymilk, one-half cup of tofu or one ounce of soynuts. However, lower amounts of isoflavones were also efficacious although to a smaller extent.
Pawlowski JW, Martin BR, McCabe GP, et al. Impact of equol-producing capacity and soy-isoflavone profiles of supplements on bone calcium retention in postmenopausal women: a randomized crossover trial. Am J Clin Nutr. (2015).