[Interchangeability of the fat-to-fat-free mass ratios obtained by means arm anthropometric measures, skinfold thickness, and bioelectrical impedance].

BACKGROUND: Body fat, fat free mass and the relationship between both, the fat-to-fat-free mass ratio are useful parameters in the nutritional evaluation of the patient. The aim of this study is to evaluate the degree of agreement among the fat-to-fat-free mass ratios obtained by arm anthropometric measures (fat-muscle index, FMI), Siri equation for the sum of four skinfold thickness (body fat-muscle index, BFMISiri) and triceps skinfold (BFMItriceps) and bioelectrical impedance (BFMIOmron) methods. METHODS: This is a cross-sectional study. A total of 145 patients were evaluated by anthropometry and bioelectrical impedance (Omron BF 300), being estimated the agreement through the Intraclass Correlation Coefficient (ICC) and Bland-Altman method. The reference method was BFMISiri. RESULTS: The ICC between BFMISiri-BFMItriceps were 0.9304 (0.9035; 0.9498), between BFMISiri-FMI of 0.7726 (0.6846; 0.8361) and between BFMISiri-BFMIOmron of 0.9114 (0.8771; 0.9361). BFMItriceps (limits of agreement -0.171 to 0.117) show the best agreement according to Bland-Altman analysis with BFMISiri, followed by BMFISiri-BFMIOmron (-0.186; 0.178). The agreement limits between FMI and BFMISiri (-0.2; 0.42), BFMItriceps (-0.26; 0.42) or BFMIOmron (-0.292; 0.504) were beyond of the established cut-off points (-0.2; 0.2). CONCLUSIONS: Due to the nature of the statistical agreement BFMItriceps and BFMIOmron are methods interchangeable methods between them and with BFMISiri. FMI is not interchangeable with BFMISiri, BFMIOmron or BFMItriceps. These results suggest that FMI cannot estimate properly the body composition. BFMItriceps and BFMIOmron are valid alternative methods to be used instead BFMISiri in the fat-to-fat-free mass ratio assessment.