Comparison of bioelectrical impedance analysis and dual-energy X-ray absorptiometry for the assessment of appendicular body composition in anorexic women

Abstract

Objective: To establish the accuracy of bioelectrical impedance analysis (BIA) for the assessment of appendicular body composition in anorexic women. Design: Cross-sectional study. Setting: Outpatient University Clinic. Subjects: A total of 39 anorexic and 25 control women with a mean (s.d.) age of 21 (3) y. Methods: Total, arm and leg fat-free mass (FFM) were measured by dual-energy X-ray absorptiometry and predicted from total and segmental BIA at 50 kHz. The predictor variable was the resistance index (Rl), that is, the ratio of height 2 to body resistance for the whole body and the ratio of length 2 /limb resistance for the arm and leg. Results: Predictive equations developed on controls overestimated total, arm and leg FFM in anorexics (Po0.0001). Populationspecific equations gave a satisfactory estimate of total and appendicular FFM in anorexics (P ¼ NS) but had higher percent root mean square errors (RMSEs%) as compared to those developed on controls (8% vs 5% for whole body, 12% vs 10% for arm and 10% vs 8% for leg). The accuracy of the estimate of total and leg FFM in anorexics was improved by adding body weight (Wt) as a predictor with Rl (RMSE% ¼ 5% vs 8% and 7% vs 10%, respectively). However, the same accuracy was obtained using Wt alone, suggesting that in anorexics, BIA at 50 kHz is not superior to Wt for assessing total and leg FFM. Conclusion: BIA shows some potential for the assessment of appendicular body composition in anorexic women. However, Wt is preferable to BIA at 50 kHz on practical grounds. Further studies should consider whether frequencies 450 kHz give better estimates of appendicular composition in anorexics as compared to Wt.

Evaluation of air-displacement plethysmography and bioelectrical impedance analysis vs dual-energy X-ray absorptiometry for the assessment of fat-free mass in elderly subjects

“…The limits of agreement of FFM estimates obtained from ZI 100 were two times wider in males (À12.2 to 12.2 kg) than in females (À6.8 to 6.8 kg) and in both cases there was evidence of negative proportional bias. As we have observed in many of our studies of four-polar BIA (Bedogni et al, 2003), weight was more accurate than ZI at predicting FFM. The only advantage of the combination of weight and ZI 100 was a modest decrease of the bias in females (from À5.6 to 5.6 kg to À5.0 to 5.0 kg).…”

“…Selection of variables for FFM prediction algorithms was carried out by stepwise bootstrapped linear regression on 1000 random samples of 68 subjects (Harrell, 2001). Candidate predictors were gender, age, weight and ZI at frequencies of 5, 50 and 100 kHz (Bedogni et al, 2003). Predictors identified at bootstrap analysis were entered into multiple regression models with standard errors of coefficients calculated by bootstrap analysis on 1000 random samples of 68 subjects (Gonçalves and White, 2005).…”

Cross-validation of bioelectrical impedance analysis for the assessment of body composition in a representative sample of 6- to 13-year-old children

“…In our previous research performed in adults, we have consistently found that RI8 contributes more than weight to the prediction of total body water, extracellular water and FFM (Bedogni et al, 2002(Bedogni et al, , 2003aMalavolti et al, 2003;Medici et al, 2005), contrarily to what happens for RI4 (Bedogni et al, 2003b;Bertoli et al, 2007). The analysis of the KISS data confirms that weight contributes more than RI4 and less than RI8 to the prediction of FFM in young children.…”

“…An octopolar (8-BIA) multifrequency implementation of BIA with tactile electrodes was recently made available on the market (Bedogni et al, 2002). Contrarily to 4-BIA (Bedogni et al, 2003b;Bertoli et al, 2007), 8-BIA was consistently found to contribute more than anthropometry to the prediction of body composition (Bedogni et al, 2002;Malavolti et al, 2003;Medici et al, 2005). However, 8-BIA has not been directly compared to 4-BIA and has been validated only for selected physiological and clinical conditions (Bedogni et al, 2002;Malavolti et al, 2003;Medici et al, 2005;Sartorio et al, 2005).…”

Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis

“…We have the policy of systematically testing this hypothesis in our BIA studies. For instance, we have not been able to show that four-polar BIA at 50 kHz is more accurate than Wt in estimating TBW and appendicular body composition in anorexic women (Scalfi et al, 1997;Bedogni et al, 2003b). Even if the use of multifrequency instruments may change this evidence, the use of an impedance-meter is clearly not justified in these circumstances.…”