Assessment of research-based body composition techniques in healthy elderly men and women using the 4-compartment model as a criterion method.

OBJECTIVE: To examine the accuracy, precision and bias of body fat estimates using traditional research based techniques, relative to those derived from a 4-compartment model in healthy, older men and women. DESIGN AND
SUBJECTS: Cross-sectional comparison of various body composition techniques in 41 healthy women (68.2 +/- 6.6 y) and 41 healthy men (70.2 +/- 7.0 y) with an age range of 57-90 y.
METHODS: Fat mass (FM) by the 4-compartment (4C) model was compared to that derived by dual energy X-ray absorptiometry (DXA), underwater weight (UWW) and total body water (TBW).
RESULTS: On a group mean basis, FM by the 4C model (24.4 +/- 7.4 kg in women, 18.2 +/- 7.6 kg in men) was similar to other techniques. The regression between FM by 4C and DXA significantly deviated from the line of identity (FM by 4C = 0.76*FM by DXA + 5.9 kg for women; 0.81*FM by DXA + 3.4 kg for men). FM by UWW was similar to FM by 4C model in men but not women (FM by 4C = 0.87*FM by UWW + 4.3 kg). FM by TBW was similar to FM by 4C model in women, but not men (FM by 4C = 0.80*FM by TBW + 4.7 kg). For DXA, there was no significant bias in estimates of FM in men or women. For UWW, there was significant bias in men with an over-estimate of FM among leaner subjects and under-estimates in fatter subjects. For TBW data, there was a significant bias in men with an under-estimate of FM among leaner subjects and over-estimate in fatter subjects.
CONCLUSIONS: Individual estimates of FM by DXA can be improved by correction factors that calibrate experimental data to standards such as the 4-C model. The assumptions of the Siri 2 compartment model are appropriate in healthy elderly men but not women, where a new equation is suggested. Inaccuracies in FM from TBW data are likely to be explained by age-related changes in the hydration of fat free mass (FFM).