MEASUREMENT OF BODY-FAT IN YOUNG AND ELDERLY WOMEN - COMPARISON BETWEEN A 4-COMPARTMENT MODEL AND WIDELY USED REFERENCE METHODS

Body composition was measured in twenty young females aged 19-27 years and eighteen elderly females, aged 65-78 Sears by densitometry (under water weighing), deuterium oxide dilution and dual-energy Xray absorpt iometry (DXA), From body weight, bone-mineral content, total body wate r and body density, percentage body fat (BF%) was calculated using a f our-compartment model, BF% obtained 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-compa rtment model minus the single methods were 2.1 (SD 1.2) for densitomet ry, 3.1 (SD 1.8) for DXA and -0.6 (SD 0.9) BF% for deuterium oxide dil ution 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 m odel (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 an d 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 b iases compared with the four-compartment model, but that a three-compa rtment model calculated from density and total body water offers an ac ceptable alternative, The difference in calculated density of the fat- free mass beta een the young and the elderly women shows the need to a dapt Siri's formula for specific groups.