RESUMEN
INTRODUCTION: Measuring body composition is an important issue to phenotype patients with obesity and to follow the nutritional care efficiency. Bioelectrical Impedance Analysis (BIA) is a simple and rapid technique. However, validity of BIA in patients with obesity remains controversial. Thus, we aimed to evaluate the validity of several BIA equations to assess body composition in a large cohort of patients with obesity by using dual X ray absorptiometry (DXA) as reference. METHODS: Seven BIA equations have been retrospectively applied on electrical data measured by BIA in patients with obesity with BMI equal or higher than 30 kg/m2 and results were compared to DXA-derived fat mass (FM) and fat-free mass (FFM). BIA and DXA were done the same day after an overnight fasting. Results were compared with Bland-Altman method and Pearson correlation. We also calculated the accuracy defined as the percentage of patients with DXA-BIA difference within ± 10% of DXA measures for FFM and FM. RESULTS: Data from 2134 patients with class I and II obesity (ob1/2, n = 1452, 47.4 ± 14.2 y; 35.0 ± 2.7 kg.m-2) and class III obesity (ob3, n = 682, 48.2 ± 13.9 y; 44.1 ± 3.5 kg.m-2) were analyzed. The best results to evaluate FFM both in ob1/2 and ob3 groups were obtained with Roubenoff's equation: Bland Altman bias at -1.96 and -0.82 kg, Pearson correlation r at 0.93 and 0.87, accuracy at 75.7% and 83.3%, respectively. However, limits of agreements at 95% were high: [-9.42; 5.49 kg] and [-8.16; 6.52 kg]. For FM evaluation, Roubenoff's equation also showed best results for ob1/2 group (bias at -1.17 kg; correlation r at 0.89 and accuracy at 79.1%) but not for ob3 group. In this latter group, Deurenberg's equation exhibited the best results (bias at 2.09 kg; correlation r at 0.81 and accuracy at 76.8%). However, limits of agreements remained high. CONCLUSION: In patients with obesity, Roubenoff BIA equation should be recommended to assess fat free mass, even if limits of agreements remain high.
