Preventive Effect of Dietary Fermented Soybean on Bone Loss in Ovariectomized Rats

The effect of experimental diets with fermented soybean (natto) containing isoflavone and zinc on ovariectomy (OVX)-induced bone loss was investigated. Sham-operated rats or OVX rats were given experimental diets containing soybean protein for 3 months, and other OVX rats were fed dietary natto, with or without calcium, calcium plus zinc, calcium plus isoflavone or calcium plus zinc and isoflavone for 3 months. Experimental diets contained 2.1 to 9.7mg zinc per 100g and 44.6 to 92.4mg isoflavone (including genistin, genistein, daidzin, and daidzein) per 100g. OVX caused a significant reduction in the dry weight and mineral density of the femur. Also, the calcium content, zinc content and alkaline phosphatase activity in femoral-diaphyseal and metaphyseal tissues was significantly reduced by OVX. These reductions were largely prevented by feeding natto diets. This prevention was significantly enhanced in OVX rats fed natto diets supplemented with isoflavone and zinc. This study demonstrates that the prolonged intake of dietary natto supplemented with isoflavone and zinc has a preventive effect on OVX-induced bone loss, suggesting that it may have a role in the prevention of osteoporosis.