Soybean isoflavones dose-dependently reduce bone turnover but do not reverse established osteopenia in adult ovariectomized rats

We assessed the dose-dependent effects of daily soybean isoflavone (IF) con sumption in reversing bone loss in adult ovariectomized rats. On d 0, femal e Wistar rats (7 mo old; n = 55) were either sham-operated (SH; n = 14) or ovariectomized (n = 41), On d 80, intermediate rats (SH: n = 5; ovariectomi zed: n = 5) were killed to confirm the ovariectomy-induced bone loss. The r emaining ovariectomized rats were randomly assigned to one of four groups o f nine rats each and fed soybean IF (mixed with a soy protein-free semipuri fied diet) at 0 (OVX), 20 (IF20), 40 (IF40) or 80 (IF80) mg/(kg body d) for 84 d. Simultaneously, SH rats were fed the semipurified diet without any a dditional compound and killed on d 164, as were the other rats. As expected , both bone mineral density in the total femur and in its diaphyseal and me taphyseal subregions and cancellous bone area/measured surface in the dista l femur metaphysis were lower in OVX than in SH rats (P < 0.05), OVX rats h ad higher plasma osteocalcin concentration and urinary deoxypyridinoline ex cretion than SH rats (P < 0.05). On d 164, osteocalcin and deoxypyridinolin e concentrations were lower in IF40 or IF80 rats than in OVX rats (P < 0.05 ). Nevertheless, neither bone mineral density nor cancellous bone area was greater in IF-fed rats than in OVX rats, Therefore, in adult ovariectomized rats, daily soybean IF consumption decreased bone turnover but did not rev erse established osteopenia.