Abstract
To establish the accuracy of bioelectrical impedance analysis (BIA) for the assessment of appendicular body composition in anorexic women. Cross-sectional study. Outpatient University Clinic. A total of 39 anorexic and 25 control women with a mean (s.d.) age of 21 (3) y. 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. Predictive equations developed on controls overestimated total, arm and leg FFM in anorexics (P<0.0001). Population-specific equations gave a satisfactory estimate of total and appendicular FFM in anorexics (P=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%=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. 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 >50 kHz give better estimates of appendicular composition in anorexics as compared to Wt. University of Napoli.
Highlights
As changes in appendicular fat and fat-free tissues are typical features of malnutrition, anthropometric measurements of limb composition have long been employed as nutritional and prognostic indicators (Heymsfield et al, 1982, 1984)
The validation of anthropometry and Bioelectrical impedance analysis (BIA) for the assessment of appendicular body composition has been traditionally performed against computed tomography (CT) and magnetic resonance imaging (MRI) (Brown et al, 1988; Fuller et al, 1999b; Elia et al, 2000)
Since dual-energy X-ray absorptiometry (DXA) is less invasive and/or more readily available than CT or MRI, it has a great potential for the validation of bedside techniques such as BIA
Summary
As changes in appendicular fat and fat-free tissues are typical features of malnutrition, anthropometric measurements of limb composition have long been employed as nutritional and prognostic indicators (Heymsfield et al, 1982, 1984). Bioelectrical impedance analysis (BIA) is a simple and noninvasive technique with a high potential for the assessment of limb composition (Brown et al, 1988; Heymsfield et al, 1998; Pietrobelli et al, 1998; Fuller et al, 1999a; Nunez et al, 1999; Elia et al, 2000; Lukaski, 2000; Tagliabue et al, 2000). Previous comparisons of BIA with DXA have shown that BIA gives accurate estimates of appendicular fat-free tissues in healthy and overweight subjects (Brown et al, 1988; Heymsfield et al, 1998; Pietrobelli et al, 1998; Fuller et al, 1999a; Nunez et al, 1999; Elia et al, 2000; Lukaski, 2000; Tagliabue et al, 2000). Besides offering a more thorough evaluation of the BIA technique, these data may have prognostic implications such as it has been shown for anthropometry (Heymsfield et al, 1982, 1984)
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