Prolonged intake of fermented soybean diets with supplementation of isoflavone and saponin prevents bone loss in ovariectomized rats

The effect of experimental diets with fermented soybean (natto) containing soybean extract (nijiru) on ovariectomy (OVX)-induced bone loss was investigated. Experimental diets containing either natto (46%), natto with 3.8% nijiru supplementation or natto with 9.8% nijiru were freely given to sham-operated rats or OVX rats for 3 months. Nijiru contained saponin (660 mu g/g of dry nijiru) and isoflavone including daidzin (770 mu g/g) and genistin (580 mu g/g) of comparatively higher concentration. OVX caused a significant reduction in the dry weight, mineral density and mineral content of the femur. The calcium content in the femoral-metaphyseal tissues was significantly reduced by OVX and these reductions were largely prevented by the feeding of natto diets with nijiru (9.8%) supplementation. This study demonstrates that the intake of natto diets supplemented with nijiru containing isoflavone and saponin has a preventive effect on OVX-induced bone toss, suggesting that it may have a role in the prevention of osteoporosis.