Dietary Soybean Protein Prevents Bone Loss in an Ovariectomized Rat Model of Osteoporosis

Abstract

The purpose of this study was to examine whether soybean protein isolate prevents bone loss induced by ovarian hormone deficiency. Thirty-two 95-d-old Sprague-Dawley rats were randomly assigned to four treatment groups [sham-operated (sham); ovariectomized (ovx); ovx+soybean; ovx + 17 beta-estradiol (E2)] and killed after 30 d. Rats in the sham, ovx and ovx + 17 beta-estradiol groups were fed a casein-based diet, and the soybean group was fed soybean protein isolate instead of casein; the diets were otherwise comparable. Rats in the ovx group had significantly lower densities of the right femur (P < 0.001) and the fourth lumbar vertebra (P < 0.05) than rats in the sham group. These lower bone densities were not observed in animals receiving 17 beta-estradiol or fed soybean. The ovx group also had significantly (P < 0.01) greater serum concentrations of 1,25-dihydroxycholecalciferol than the other three groups. Our findings suggest that dietary soybean protein is effective in preventing bone loss due to ovarian hormone deficiency. Because serum activities of both alkaline phosphatase and tartrate-resistant acid phosphatase were significantly greater in the ovx group and in the ovx + soybean group but not in the group receiving 17 beta-estradiol, compared with sham animals, this confirms that ovariectomy enhances and 17 beta-estradiol suppresses the rate of bone turnover. Despite the higher rate of bone turnover in the soybean-fed animals, the vertebral and femoral bone densities of these rats were significantly greater than those of rats in the ovx group, suggesting that formation exceeded resorption. Further studies are needed to clarify whether this protective effect on bone is due to the protein itself or to the presence of isoflavones in soybean protein.

Evaluation of the Preventive Effect of Isoflavone Extract on Bone Loss in Ovariectomized Rats

“…Treatment with isoflavone extract at 6.25 g/kg appeared to prevent bone loss in the femur and lumbar vertebra. These results are supported by previous observations of the positive effects of soybean products -such as soybean protein and soy milk powder -on the bone density of female rats, 8,12,13) because these products contained genistein and daidzein. But, the effects of isoflavone on ALP and TRAP activities are not the same as that of estrogen.…”

“…24) Our data on uterine weight, bone density, bone calcium, and bone ash weights confirm the observations of other investigators that bone loss in the OVX rat is prevented by estrogen administration, and that estrogen can also suppress the OVX-induced rise in two biochemical makers of bone turnover: serum ALP and TRAP. 9,13) As expected, the femurs and fourth-lumbar vertebral bones of rats in the OVX-C group had lower values for bone density and mineral content than those of in the SHAM group. Treatment with isoflavone extract at 6.25 g/kg appeared to prevent bone loss in the femur and lumbar vertebra.…”

“…The authors speculated that this beneficial effect was due to enhanced intestinal absorption of calcium. Arjmandi et al 13) found that feeding soy protein to ovariectomized rats prevented bone loss. Goyal et al 14) showed that this positive effect was due to the isoflavone in the soy.…”

“…Soy isoflavones, which have both weak estrogenic and antiestrogenic effects, are structurally similar to tamoxifen, an agent that acts similarly to estrogen in reducing postmenopausal bone loss. 8,12,13) The biological effects of genistein and daidzein have not been fully clarified. Daidzein has been shown to have a y To whom correspondence should be addressed.…”

The possibility of genistein as a new direct pulp capping agent

“…It has been reported that genistein has stronger estrogen-like effect than the other flavonoids 6) , induce the activation of osteoblasts and increase the bone mass, and said to be effective in improvement and prevention of osteoporosis 8,9) . Soy isoflavones are also highly safe 10,11) because it is a natural ingredient derived from food, so side effects such as osteonecrosis of the jaw caused by osteoporosis bisphosphonate drug therapy has not been reported.…”