Dietary Ungerminated and Germinated Soybean Supplementation Improves Bone Mineralization and Strength in Growing Male Rats

It has been thought that soybean products rich in phytoestrogenic isoflavones are effective in promoting bone metabolism in ovariectomized rats. However, it is not clear if such an effect can be changed by germination of soybean and can be observed in growing males. The present study was undertaken to determine the effects of different concentrations of dietary ungerminated and germinated soybean (UGS and GS, respectively) on bone metabolism in young male rats. Forty-nine 6-week-old male Sprague-Dawley rats were assigned to seven dietary treatment groups: AIN 93G (control); control with UGS powder at 3% (UGS-L), 15% (UGS-M), or 30% (UGS-H); and control with GS powder at 3% (GS-L), 15% (GS-M), or 30% (GS-H). The biomarkers of bone metabolism (plasma and urinary Ca and P) and the physical properties and mineral content of bones were measured. Plasma osteocalcin and urinary deoxypyridinoline levels were not affected by soybean diets. The plasma P level was significantly elevated by dietary soybeans (P < .001). However, there was a negative correlation (r = -0.555) between plasma P level and dietary UGS level (P < .01). Between the UGS and GS groups, the P level of the GS-M group was significantly higher than that of the UGS-M group (P < .001). The tibial weight was decreased with low to medium doses of soybeans, but not with higher levels. Femoral bone strength was improved in the UGS-H, GS-M, and GS-H groups. The P contents of femoral and tibial bones were increased in all UGS groups as well as in GS-M and GS-H groups. In conclusion, soybean supplementation in young growing male rats improved bone mineralization and bone strength.