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Soy protein has a greater effect on bone in postmenopausal women not on hormone replacement therapy

. Menopausal women are at increased risk for osteoporosis due to declining estrogen levels. Many of these women take hormone replacement therapy to prevent osteoporosis. Although HRT slows bone loss, its long-term use does not reduce the incidence of fractures. Menopausal women are more likely to seek natural therapies such as diet, herbs, or supplements. Soy isoflavones may act as weak estrogens and may have an effect on bone tissue. Recent studies suggest that soy proteins and isoflavones may reduce the risk of osteoporosis in menopausal women. Picherit et all showed in their study "Daidzein is more efficient than genistein in preventing ovariectomy induced bone loss in rats" (J. Nutr. 130:1675-1681) and "Soy isoflavones dose dependently reduce bone turnover but do not reverse established osteopenia in adult ovariectomized rats" (J. Nutr. 131:723-728) that soy isoflavones may prevent bone loss. Other studies have shown that soy protein intake is associated with reduced calcium loss in postmenopausal women. The aim of this study was to investigate whether soy protein intake could influence bone metabolism in postmenopausal women. The study included women who were taking hormone replacement therapy and women who were not taking hormone replacement therapy. A total of 71 women were divided into two groups: the soy protein group (received soy protein as a protein source) and the dairy group (received milk-based protein). Serum and urinary markers of bone turnover were measured. Both groups showed a positive effect on serum insulin-like growth factor-I (IGF-I), an indicator of bone formation. There were significant differences in biomarkers of bone formation:

• Compared to the dairy group, the soy protein group had a more pronounced effect on IGF-I. The role of IGF-I in bone formation is still unclear, but there is evidence that IGF-I may stimulate collagen formation.
• Urinary deoxypyridinoline excretion was significantly reduced only in the soy protein group. Urinary deoxypyridinoline excretion is a biomarker for bone resorption.
• Only the women who consumed dairy protein showed increased urinary calcium excretion. The decrease in urinary calcium excretion could be explained by the low content of sulfur-containing amino acids in soy protein.

When women taking hormone replacement therapy and those not taking hormone replacement therapy were studied, the effect of soy protein was shown to be greatest in women not taking hormones. Soy protein significantly reduced urinary deoxypyridinoline levels in women not treated with hormone replacement therapy.

The results suggest that soy protein may have a beneficial effect on bone health, particularly in women not taking hormone replacement therapy. Soy protein appeared to reduce bone loss by suppressing bone resorption and increasing the rate of bone formation.
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Bahram H. Arjmandi, Dania A. Khalil, Brenda J. Smith, Edralin A. Lucas, Shanil Juma, Mark E. Payton and Robert A. Wild (The Journal of Clinical Endocrinology and Metabolism Vol. 88, No. 3 1048-1054)