THE EFFECT OF SOYBEAN PROTEIN ON BONE LOSS IN A RAT MODEL OF POSTMENOPAUSAL OSTEOPOROSIS

This study was designed to investigate the modulatory effect of dietar y soybean protein on the skeleton of an ovariectomized rat model with postmenopausal osteoporosis. Thirty-two female Sprague-Dawley rats wer e weight matched and divided into the following four experimental grou ps: Soy group, ovariectomized and fed soy protein diet; Estrogen group , ovariectomized, fed casein diet and injected with estrogen; Casein g roup, ovariectomized and fed casein diet; and Sham group, sham-operate d and fed casein diet. The diets and estrogen were started two weeks a fter surgery, and continued for four weeks, Rats in the Sham, Soy and Estrogen groups had significantly higher (p < 0.05) femur and tibia as h content than those in the Casein group. Accordingly, the calcium con tent of the tibia and femur were also significantly higher (p < 0.05) in the Soy, Estrogen and Sham groups as compared to the Casein group. Serum total and bone-type alkaline phosphatase levels were both signif icantly lower (p < 0.05) in the Estrogen and Sham groups in relation t o the Soy and Casein groups. This study demonstrated that a 22% soybea n protein diet could be just as effective as daily estrogen administra tion in suppressing bone loss due to ovariectomy. However, unlike estr ogen, soy protein diet did not have any uterotrophic effect and did no t decrease the markers of bone turnover measured, suggesting a possibl e difference in the mechanism of action.