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Comparative assessment of change in fat mass using dual X-ray absorptiometry and air-displacement plethysmography


Dr M Buchowski, 1161 21st Avenue South, Medical Center North, Room A4103, Nashville, TN 37232-2260, USA. E-mail:


What is already known about this subject

  • • Excess fat mass (FM) is believed to be a primary cause of the health risks (e.g. cardiovascular, metabolic) associated with obesity
  • • Dual X-ray absorptiometry and air-displacement plethysmography are frequently used in clinical research and practice to measure body composition changes.
  • • There is no accepted single tool for measurement of obesity and change in FM that provides a sufficiently accurate and precise estimate.

What this study adds

  • • The demonstrated accuracy of dual X-ray absorptiometry (DXA) supports its use as an indirect method for monitoring fat mass (FM) changes associated with clinical interventions for obesity.
  • • DXA is significantly more accurate when compared to air-displacement plethysmography in recognizing small changes in FM.


The study aims to compare the accuracy of body composition measurements to small, defined changes in fat mass (FM) between dual X-ray absorptiometry (DXA) and air-displacement plethysmography (ADP). Fifty-six healthy adults, 29 women and 27 men (age, 38 ± 12.4 years; body mass index, 27.6 ± 5.8 kg m−2) were included in the study. Exclusion criteria were pregnancy, indwelling metal hardware or pacemakers, or weight exceeding DXA table limit (>350 lb). All individual testing was completed within a 2-h period. Fat packets were prepared using lard wrapped in plastic and applied exogenously in defined locations. Each participant completed body composition measurements with ADP and DXA (both testing modalities completed with and without 1 kg of exogenously applied FM). Both DXA and ADP were highly accurate in detecting an overall increase in body mass associated with exogenously applied 1 kg of FM (0.99 kg vs. 0.97 kg, respectively). DXA more accurately detected exogenous fat increase as FM compared to ADP (0.93 kg; 90% CI for the mean of the difference: 0.83 to 1.03 kg vs. 0.45 kg; 90% CI: 0.19 to 0.71 kg, respectively). The accuracy of body mass detection was similar for males and females (0.97 vs. 1.02 for DXA and 0.92 vs. 1.02 for ADP, respectively), though accuracy in detecting added mass as fat was less accurate in males than females (0.84 vs. 1.00 for DXA and 0.39 vs. 0.51 for ADP, respectively). Both DXA and ADP are accurate in detecting an overall increase in body mass associated with exogenously applied 1 kg of FM. However, DXA is more accurate than ADP in correctly identifying the increase in body mass as FM, as opposed to fat-free mass.

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