Moderate energy restriction increases bone resorption in obese postmenopausal women

Background: Weight reduction reduces bone mineral density (BMD) and increases the risk of osteoporosis. Objective: We investigated whether bone is mobilized in postmenopausal women during energy restriction and whether hormones regulate bone turnover and mass. Design: Twenty-seven obese postmenopausal women with a mean (±SD) age of 55.9 ± 7.9 y and body mass index (in kg/m²) of 33.0 ± 3.8 completed the 6-mo study. Fourteen women followed a moderate energy-restricted diet (WL group) and 13 control subjects maintained their body weight (WM group). Body weight, bone turnover markers, serum parathyroid hormone (PTH), and dietary intake were measured throughout the study. Total-body BMD, sex hormone binding globulin, leptin, and estrone were measured at baseline and at week 25. Results: In the WL group, body weight decreased by 10.2 ± 5.5% (P < 0.001), body fat mass decreased by 18.7 ± 11.3% (P < 0.001), and total-body BMD decreased by 1.2 ± 1.2%; these changes were significantly different from those in the WM group (P < 0.05). Serial measurements showed chronically elevated rates of bone resorption and formation during energy restriction that were greater than in the WM group (P < 0.05). Serum sex hormone binding globulin increased and leptin decreased with weight loss (P < 0.05). Serum PTH tended to increase in the WL group but not in the WM group (P < 0.06). The reduction in fat mass with weight loss was directly associated with a decrease in serum estrone (P < 0.01, R² = 0.50). Conclusions: Moderate energy restriction increases bone turnover in obese postmenopausal women and may be regulated in part by alterations in serum PTH and estrone.