Soy isoflavones have been reported to prevent bone loss in rat models of osteoporosis. However, the effect of the natural soybeans that people consume in their diet needs to be explored. In the present study, we evaluated the effects of yellow and black soybeans (Glycine max), and sword beans (Canavalia gladiate) on bone mineral density (BMD), bone mineral content (BMC), and bone biomarkers in ovariectomized (OVX) rats.
Seven-week-old female Sprague-Dawley rats were raised for 2 weeks on a calcium-free diet based on the American Institute of Nutrition (AIN)-93M diets. All the rats received OVX, were randomized to one of four groups, and given one of the diets supplemented with casein, yellow soybean, black soybean, and sword bean for 10 weeks. BMD, BMC, osteocalcin (OC; a bone formation biomarker), deoxypyridinoline (DPD; a bone resorption biomarker), and TNF-alpha (a bone resorption cytokine) were assessed.
In the femur and lumbar spine, BMD and BMC were significantly higher in the various bean groups than in the casein group. Among the bean groups, femur and spine BMD were significantly higher in the yellow soybean and sword bean groups than in the black soybean group. Femur BMC was the highest in the yellow soybean group, and spine BMC was not significantly different between the various bean groups. Plasma OC concentrations and urinary DPD excretion were significantly higher in the casein group than in the various bean groups. The sword bean group showed significantly lower OC and DPD levels than the yellow and black soybean groups. There were no significant differences between the yellow and black soybean groups. TNF-alpha concentrations were not significantly different between the four groups.
Consumption of yellow and black soybeans, and sword beans had a definite protective effect on bone loss in OVX rats by inhibiting bone turnover and preventing bone resorption. Furthermore, consumption of sword beans may help prevent postmenopausal osteoporosis.