EFFECT OF WEIGHT-LOSS ON BONE-MINERAL CONTENT AND BONE-MINERAL DENSITY IN OBESE WOMEN

Studies of body-composition changes during weight loss have had confli cting results with regard to changes in bone mineral content (BMC) and bone mineral density (BMD). We examined BMC and BMD for changes durin g weight loss. Fourteen women enrolled in a 15-wk weight loss program. Dual-energy X-ray absorptiometry (DXA) measures of the total body wer e made at baseline (T1), the midpoint of weight loss (T2), and at the end of weight loss (T3). Body weight changed significantly throughout the 15 wk, declining from a high of 89.7 +/- 3.6 to 74.1 +/- 3.2 kg. F at-free mass declined initially (47.8 +/- 1.7 kg at T1, 45.7 +/- 1.4 k g at T2, and 46.0 +/- 1.5 kg at T3) and then stabilized. Fat mass chan ged significantly during the study (39.2 kg at T1, 32.4 kg at T2, and 29.3 kg at T3). No significant differences were observed in BMC or bon e areal measurement during the study. However, BMD declined significan tly from baseline (1.217 g/cm(2) at T1, 1.197 g/cm(2) at T2, and 1.200 g/cm(2) at T3). The changes in BMC and BA were in opposite directions , resulting in a significant decline in BMD without a loss of BMC. The se data suggest that changes in BMD observed with weight loss may be t he result of a lack of instrument sensitivity when body weight and com position change and are simply an artifact and not a physiologic chang e in BMD. Further research is needed to determine the full effect of w eight loss on BMC, bone area, and BMD.