NEW BRUNSWICK , N.J.—Data from a recent study supports the hypothesis energy restriction in lean rats compared with obese rats is more detrimental to bone, and it is possible the greater decline in estrogen and lower levels of 25-hydroxyvitamin D (25OHD) contribute to this effect (J Nutr. 2010;140(1):31-37). Researchers aimed to determine how bone mineral density (BMD) and geometry respond to energy restriction in mature obese rats compared with lean rats. At 6 months of age, 36 diet-induced obese and lean female Sprague-Dawley rats were allocated to control (CTL; ad libitum; n=18) and energy-restricted (EnR; 40 percent restriction; n=18) diets. After 10 weeks of dietary intervention, obese EnR rats lost more weigh than lean EnR rats (P<0.02), whereas body weight did not change significantly in the two CTL groups. Only the lean EnR (and not obese EnR) rats showed lower BMD compared with CTL rats at the tibia, distal and proximal femur and femoral neck, and trabecular bone volume (P<0.05). Serum estradiol declined in lean EnR rats compared with baseline (P<0.05), but not in the obese EnR rats. In addition, the final 25OHD concentration was higher (P<0.05) in obese than in lean EnR rats. Serum parathyroid hormone decreased (P<0.05) from baseline to final in lean and obese CTL, but not EnR rats.
