Menopausal estrogen loss leads to an increased bone loss. Soy isoflavones can act as selective estrogen receptor modulators but studies evaluating their effects on bone have produced mixed results.
To evaluate the effects on bone turnover markers, British researchers enrolled 200 early postmenopausal women into a 6-month trial. Women were randomized to receive either 15 g soy protein devoid of isoflavones or the same amount of protein that provided 66 mg isoflavones. Mean isoflavone intake among older Japanese is about 40 mg/day.
At study conclusion the higher isoflavone soy protein reduced bone resorption more than it reduced bone formation thereby exerting a net beneficial effect on bone. In addition, the isoflavone-containing soy protein reduced fasting glucose, fasting insulin, insulin resistance and systolic blood pressure whereas no significant changes in these parameters were observed with the soy protein devoid of isoflavones. However, soy protein rich in isoflavones also increased thyroid stimulating hormone levels and decreased free thyroxine concentrations although both values remained well within the normal range.
The authors of this study concluded that soy protein with isoflavones may confer a beneficial effect on bone health, analogous to the mode of action of anti-resorptive agents and may also reduce cardiovascular disease risk.
Sathyapalan, T., Aye, M., Rigby, A. S., Fraser, W. D., Thatcher, N. J., Kilpatrick, E. S., & Atkin, S. L. (2016). Soy Reduces Bone Turnover Markers in Women During Early Menopause - a Randomized Controlled Trial. J Bone Miner Res.