Consumption of legumes improves certain bone markers in ovariectomized rats

Soybeans are known to protect against osteoporosis, but other legumes frequently consumed in Asia have not been studied to learn if they have a similar protective effect. This study investigated the hypothesis that consumption of soybean, mung bean, cowpea, and adzuki bean has beneficial effects on bone biomarkers in ovariectomized rats. Female Sprague-Dawley rats were either sham operated (sham; n = 7) or surgically ovariectomized and then fed a regular AIN-93M diet (OVX; n = 7) or AIN-93M containing soybean (n = 7), mung bean (n = 7), cowpea (n = 7), or adzuki beans (n = 7) for 10 weeks. No bean consumption significantly altered the body, subcutaneous fat, or uterus weight; however, consumption significantly increased the serum calcium/phosphorous ratio and decreased urinary calcium excretion compared with those of the OVX group. Serum concentration of 17β-estradiol was significantly lower in the OVX group compared with that of the sham group and was lowest in the group fed OVX diet containing soybean. Serum osteocalcin concentration was significantly higher in all OVX rats given a diet with beans compared with the same diet without, but urinary deoxypyridinoline excretion was lowest in the group fed OVX diet containing cowpea. There were no significant differences in bone mineral density or bone mineral content of the right femur, tibia, or lumbar spine or in the trabecular bone volume of the tibia among the diet groups. In conclusion, the consumption of soybean, mung bean, cowpea, and adzuki bean in OVX rats improved osteocalcin, but only those fed cowpea showed decreased bone resorption biomarker, suggesting that cowpea may have the most protective effect on bone in OVX rats.