Body composition analyses by air displacement plethysmography in adults ranging from normal weight to extremely obese

OBJECTIVE To compare body composition parameters estimated by air displacement plethysmography (ADP) to dual X-ray absorptiometry (DXA) in body mass index (BMI) classifications that include extremely obese (BMI ≥ 40.0 kg/m(2) ), and to examine if differences between analyses were influenced by BMI. METHODS Fat-free mass (FFM, kg), fat mass (FM, kg), and body fat (BF, %) were analyzed with both technologies. RESULTS All outcome measures of ADP and DXA were highly correlated (r ≥ 0.95, P < 0.001 for FFM, FM, and BF), but Bland-Altman analyses revealed significant bias (P < 0.01 for all). ADP estimated greater FFM and lower FM and BF (P < 0.01 for all). BMI explained 27% of the variance in differences between FFM measurements (P < 0.001), and 37 and 33% of the variances in differences between FM and BF measurements, respectively (P < 0.001 for both). Within normal weight and overweight classifications, ADP estimated greater FFM and lower FM and BF (P < 0.001 for all), but the opposite occurred within the extremely obese classification; ADP estimated lower FFM and greater FM and BF (P < 0.05 for all). CONCLUSIONS Body composition analyses by the two technologies were strongly congruent, but systematically different and influenced by BMI. Caution should be taken when utilizing ADP to estimate body composition parameters over a wide range of BMI classifications that include extremely obese.