A comparison of air displacement plethysmography with three other techniques to determine body fat in healthy adults

Background: This study compared air displacement plethysmography (ADP), whi ch relies on measurements of body density to estimate body fat, with three other techniques that measure body composition: (1) hydrostatic weighing (H W), which also measures body density; (2) bioelectrical impedance (BIA), wh ich determines electrical resistance and total body water to estimate fat-f ree mass; and (3) dual-energy x-ray absorptiometry (DXA), which measures bo ne, fat, and fat-free soft tissue masses. Methods: ADP, HW, BIA, and DXA we re performed on 20 healthy volunteers (10 males and 10 females). The subjec ts were within 20% of ideal body weight, 31.1 +/- 1.8 years of age, and 75. 4 +/- 2.7 kg with body mass index values of 25.2 +/- 0.9 (kg/m(2)) and perc ent body fat by ADP ranging from 6.0% to 41.0%. Results: Percent body fat m easurements by the four methods were highly correlated (r >.90, p <.0001). Mean body fat as determined by ADP, HW, BIA, and DXA were 23.4% +/- 2.3%, 2 3.9% +/- 1.8%, 23.1 +/- 1.9%, and 26.4% +/- 2.4%*, respectively (*p <.05 vs ADP). There was a significantly positive slope (+0.23) for the individual differences vs the average of ADP and HW percent body fat, demonstrating a slightly negative difference at lower body fat levels and a slightly positi ve difference at greater body fat levels. Although the average percent body fat determined by ADP was similar to that by HW for the entire population, there was a significant gender difference with the average body fat measur ed by ADP being 16% less in males and 7% greater in females than that deter mined by HW. Conclusions: Body fat measurements using ADP were highly corre lated with those using KW, BLA, and DXA across a relatively wide range of b ody fat levels in healthy adults. These results support the utility of ADP as a relatively new technique in the estimation of percent body fat in heal thy adults. However, the error associated with gender and the level of body fat is not negligible and requires further investigation.