a1 Department of Human Nutrition, Wageningen Agricultural University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
Body composition was measured in twenty young females aged 19−27 years and eighteen elderly females, aged 65−78 years by densitometry (underwater weighing), deuterium oxide dilution and dual-energy X-ray absorptiometry (DXA). From body weight, bone-mineral content, total body water and body density, percentage body fat (BF%) was calculated using a four-compartment model. BF% abtained by this four-compartment model was regarded as a reference method and BF% obtained by the single methods were compared with this value. Differences in BF% from the four-compartment model minus the single methods were 2·1 (SD 1·2) for densitometry, 3·1 (SD 1·8) for DXA and -0·6 (SD 0·9) BF% for deuterium oxide dilution in the young women. In the elderly women these values were -0·6 (SD 2·3), 5·3 (SD 3·8) and 0·7 (SD 2·2) BF%. When a three-compartment model (calculated from body density and total body water) was compared with the four-compartment model, the bias was 0·4 (SD 0·3) BF% in the young and 0·0 (SD 0·3) BF% in the elderly women. From the mineral and water fractions in the fat-free mass the true density of the fat-free mass was calculated as 1·1070 (SD 0·0047) kg/l in the young females and 1·0970 (SD 0·0088) kg/l in the elderly women (P<0·001). This study shows that the single methods have considerable mean and individual biases compared with the four-compartment model, but that a three-compartment model calculated from density and total body water offers an acceptable alternative. The difference in calculated density of the fat-free mass between the young and the elderly women shows the need to adapt Siri's formula for specific groups.
(Received June 30 1995)
(Revised August 31 1995)
(Accepted September 04 1995)