COMPARATIVE-EVALUATION OF BODY-COMPOSITION METHODS AND PREDICTIONS, AND CALCULATION OF DENSITY AND HYDRATION FRACTION OF FAT-FREE MASS, IN OBESE WOMEN

The objective of this study was to apply a three-component model of bo dy composition to a group of obese women in order to (a) establish the relative value of a number of readily available prediction equations by comparison of the extent of agreement between these predictions and body composition estimated by the model and other reference methods a nd (b) evaluate density and hydration of fat-free mass. Estimation of body composition was carried out by reference methods and prediction e quations and the usefulness of these prediction equations for applicat ion specifically to obese women was evaluated. The subjects were 15 ob ese, otherwise healthy, Caucasian women (body mass index > 30kg/m(2) a nd body fat > 40% of body weight, as originally determined using densi tometry). Body composition was estimated using three established refer ence methods (deuterium dilution which primarily measures total body w ater, densitometry for body fat and fat-free mass and total body potas sium) and the three component model constructed from deuterium dilutio n and densitometry. Density and hydration fraction of the fat-free mas s were calculated from appropriate values obtained as integral parts o f the three-component model. In addition, body composition was predict ed from various prediction equations incorporating weight and height ( some of which include a factor for age), from a number of prediction e quations utilizing different terms involving the same whole-body bio-e lectrical impedance measurement and from measurements of skinfold thic kness and near infrared interactance. The extent of agreement between methods was assessed using bias and 95% limits of agreement. Mean dens ity of fat-free mass was found to be 1.104 kg/l (s.d. 0.006kg/l) with a range of 1.093 to 1.117 kg/l, and mean hydration fraction was 0.712 (s.d. 0.016) with a range of hydration from 68.2% to 75.1% (all values were calculated from the three-component model).ly a large and unacce ptable variability in estimates of body composition obtained by the va rious prediction equations applied here, and that there is a particula r risk involved in applying prediction equations, originally derived i n lean individuals, to obese women.