The effect of excessive fat tissue on the measure of bone mineral density by dual X-ray absorptiometry: the impact of substantial weight loss following sleeve gastrectomy.

PURPOSE: Dual-energy X-ray absorptiometry (DXA) is used in clinical routine to determine areal bone mineral density (aBMD). However, it is not clear whether excessive fat mass or substantial weight loss modify the aBMD measurements. The aim of this study was to evaluate the effect of soft tissue composition on aBMD measured by DXA using a clinical model (i.e. sleeve gastrectomy: SG) that induces substantial body weight loss. METHODS: Areal bone mineral density and body composition (fat mass: FM and lean tissue mass: LTM) were determined by DXA in 41 obese patients (33 women, 80.5%) just before SG and 1 month later. RESULTS: One month after SG, mean weight loss was -9.8 ± 2.6 kg, with a significant decrease in LTM and FM (kg) ranging from -7.3% to -9.5%. The relative variation in aBMD was increased at the lumbar spine (2.45 ± 3.44%) and decreased at the hip (-1.47 ± 2.28%), whereas no variation was observed for the whole body and radius. The variation in aBMD at the lumbar spine was inversely correlated with variations in weight, whole-body FM and trunk FM, but not LTM. CONCLUSION: This study shows evidence of a potential effect of body composition, particularly FM, on aBMD. However, given the modest change in aBMD, which was close to the precision error of aBMD measurements, it appears that significant weight loss does not have a clinically significant impact on the evaluation of aBMD using DXA.

Body composition changes in the first month after sleeve gastrectomy based on gender and anatomic site.

BACKGROUND: Sleeve gastrectomy (SG) induces acute weight loss, but its impact on the very early postoperative changes in body composition (BC) is less clear. OBJECTIVES: This longitudinal study examined the BC changes in the first month after SG according to gender and anatomic site. METHODS: BC (lean tissue mass [LTM] and fat mass [FM]) were determined by dual-energy x-ray absorptiometry in 41 obese patients (33 women, 80.5%) just before SG and 1 month later. SETTING: University hospital of Montpellier, France. RESULTS: One month after SG, mean weight loss was -9.8±2.6 kg, with a significant decrease in LTM and FM (kg) ranging from -7.3% to 9.5%, depending on site. FM (kg) loss in men exceeded that in women at whole body, upper limbs, and trunk. FM (%) and the LTM/FM ratio decreased only in the trunk in men and the lower limbs in women, but the gender difference was only observed for the trunk. In women, age was positively correlated with relative FM variation (% and kg) in the lower limbs and negatively correlated with LTM and LTM/FM. In men, weight was negatively correlated with the relative LTM and FM (kg) variations in the upper limbs. CONCLUSION: SG induces acute weight loss, but this loss comprises losses in both FM and LTM. Because excessive LTM loss can have deleterious consequences, preventive strategies should be implemented soon after bariatric surgery. The specific changes in BC are highlighted according to gender and anatomic site.