Assessment of body composition by air-displacement plethysmography: influence of body temperature and moisture

BACKGROUND: To investigate the effect of body temperature and moisture on body fat (%fat), volume and density by air-displacement plethysmography (BOD POD). METHODS: %fat, body volume and density by the BOD POD before (BOD POD(BH)) and immediately following hydrostatic weighing (BOD POD(FH)) were performed in 32 healthy females (age (yr) 33 ± 11, weight (kg) 64 ± 14, height (cm) 167 ± 7). Body temperature and moisture were measured prior to BOD POD(BH )and prior to BOD POD(FH )with body moisture defined as the difference in body weight (kg) between the BOD POD(BH )and BOD POD(FH )measurements. RESULTS: BOD POD(FH )%fat (27.1%) and body volume (61.5 L) were significantly lower (P ≤ 0.001) and body density (1.0379 g/cm(3)) significantly higher (P ≤ 0.001) than BOD POD(BH )%fat (28.9%), body volume (61.7 L), and body density (1.0341 g/cm(3)). A significant increase in body temperature (~0.6°C; P ≤ 0.001) and body moisture (0.08 kg; P ≤ 0.01) were observed between BOD POD(BH )and BOD POD(FH). Body surface area was positively associated with the difference in %fat independent of changes in body temperature and moisture, r = 0.30, P < 0.05. CONCLUSION: These data demonstrate for the first time that increases in body heat and moisture result in an underestimation of body fat when using the BOD POD, however, the precise mechanism remains unidentified.