Daidzein Is More Efficient than Genistein in Preventing Ovariectomy-Induced Bone Loss in Rats

We investigated the ability of genistein and daidzein, two soybean isoflavones, compared with that of 17a-ethinylestradiol, to prevent bone loss in ovariectomized rats, a model for postmenopausal osteoporosis. Female Wistar rats (n = 65; 12 mo old) were either sham-operated (SH; n = 13) or ovariectomized (OVX; n = 52). On d 0, OVX rats were randomly assigned to groups as follows: 13 received genistein [G; 10 μg/(g body weight . d)], 13 were treated with daidzein [D; 10 μg/(g body weight d)], 13 received 17a-ethinylestradiol [E 2 ; 30 μg/kg body weight d)] and 13 were untreated (OVX). Compounds were mixed with a soy protein-free powdered semipurified diet and given orally for 3 mo. On d 90, the bone mineral density (BMD) in lumbar vertebrae, femur and its metaphyseal and diaphyseal zones (rich in cancellous and cortical bone, respectively) was lower in OVX than in SH (P < 0.01). In D or E 2 , the four BMD were not different from SH, whereas in G, only the diaphyseal BMD was not different from SH. Image analysis performed in the distal femur metaphysis revealed that the cancellous bone area was lower in OVX than in SH (P < 0.01). Only the area in D was not different from that in SH. Finally, the bone turnover, which was higher in OVX than in SH (P < 0.005 and P < 0.05 for plasma osteocalcin concentration and urinary deoxypyridinoline excretion, respectively), was not different in G, D or E 2 compared with SH. Therefore, consumption of 17a-ethinylestradiol or daidzein was more efficient than genistein in preventing ovariectomy-induced bone loss in rats.