Energy restriction is associated with lower bone mineral density of the tibia and femur in lean but not obese female rats

Abstract

Energy restriction decreases bone mineral density (BMD), and epidemiological studies suggest that the risk of weight loss-induced bone loss is greater in lean than in heavier individuals. Our goal in this study was to determine how bone density and geometry respond to energy restriction in mature obese rats compared with lean rats. At 6 mo 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% restriction; n = 18) diets. After 10 wk of dietary intervention, obese EnR rats lost more weight (-61 ± 14 g) than lean EnR rats (-91 ± 34 g) (P < 0.02), whereas body weight did not change significantly in the 2 CTL groups (14 ± 23 g). 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