Evaluation of two foot-to-foot bioelectrical impedance analysers to assess body composition in overweight and obese adolescents

The objective of the present study was to determine the accuracy of two foot-to-foot (FF) bioelectrical impedance analysers (BIA) to assess body composition in overweight and obese adolescents, compared with dual-energy X-ray absorptiometry (DXA) and hand-to-foot (HF) BIA. Body composition was assessed in fifty-three overweight or obese adolescents (BMI 27.9 (SD 4.1) kg/m(2); aged 13-16 years) by DXA (Hologic QDR-4500; Hologic Inc., Bedford, MA, USA) and BIA (HF (BIA 101, RJL System, Detroit, IL, USA) and FF (Body Fat Monitor Scale BF-625, Tanita Corporation of America Inc., Arlington Heights, IL, USA; Tefal Bodymaster Vision, Tefal, Rumilly, France)). Bland-Altman tests showed that, compared with DXA, FF-Tanita and FF-Tefal underestimated (P<0.05) fat mass (FM) less than HF-BIA (-1.7 (SD 3.1), -0.7 (SD 5.8) and -2.3 (SD 2.2) kg respectively, P<0.001). However, the limits of agreement between DXA and FF-Tanita or FF-Tefal were much greater than those obtained with HF-BIA (-7.7 and +4.3, -12.0 and +10.6 v. -2.1 and +6.7 kg respectively). The differences between FM assessed using the FF-Tanita or the FF-Tefal analyser and DXA increased with the waist:hip ratio, and were higher in boys than in girls. The major limiting factor of FF-BIA was the inter-individual variability in FM estimates. In conclusion, FF-BIA and DXA are not interchangeable methods. FF-BIA could be acceptable to assess body composition in large groups of over-weight or obese adolescents, but cannot be recommended for body composition assessment in obese subjects because of the large errors in individual estimates.