Applied nutritional investigationSingle prediction equation for bioelectrical impedance analysis in adults aged 20–94 years☆
Introduction
Date accepted: September 26, 2000. Assessment of fat-free mass (FFM) and fat mass (FM) in patients optimizes nutrition support to avoid or minimize muscle wasting or obesity. Nutrition assessment should therefore include objective body-composition measurements. Bioelectrical impedance analysis (BIA) has been developed for field use and has shown great potential for use in estimating body composition; it is also easy to use, non-invasive, and inexpensive.1, 2
Many investigators have developed empiric BIA equations for prediction of FFM, total body weight, and body fat.1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 Most of these equations have been validated in relatively young, healthy adults against several body-composition techniques.9 Studies have shown that BIA formulas developed for healthy, normal-weight subjects are not suitable for obese subjects14, 15 and are not valid in elderly subjects.13
In longitudinal studies, the use of different BIA formulas in the same subject who becomes overweight or ages introduces a bias into body-composition studies and makes one question whether the differences in body composition are due to changes in the BIA formula or to changes in body composition. Thus, it would be advantageous to use a single formula that is applicable in young and elderly subjects and permits estimation of FFM and FM in overweight subjects and subjects with grade 1 obesity.
Roubenoff et al.13 and others concluded that BIA equations are subject to errors that cannot be determined a priori unless they are validated in the specific population in which they are to be applied.16, 17, 18 Thus, BIA equations must be validated in a representative population sample against a reference method before it can be accepted as accurate. BIA can be validated against dual-energy x-ray absorptiometry (DXA), hydrodensitometry, and total body potassium. DXA is one reference method3 that has been validated against independent methods such as in vivo neutron activation,5, 6 total body potassium, and hydrodensitometry.7 Recent studies have shown that DXA and hydrodensitometry agree well at high, moderate, and low levels of body fat.19 The purpose of this study was to validate, against DXA, a single BIA equation in a healthy, white European group of subjects aged 22–94 y and with body mass indexes (BMIs) of 17.0–33.8 kg/m2. A single BIA equation that is valid in subjects with different ages and BMIs for use in longitudinal studies would be a significant advantage for nutrition assessment.
Section snippets
Subjects
Three hundred forty-three healthy ambulatory white subjects (202 men and 141 women) aged 22–94 y (Table I ) were included in this study. Subjects were non-randomly recruited through advertisements in local newspapers, and invitations to participate in the study were sent to elderly members of leisure clubs. Although subjects were non-randomly selected, statistical analysis showed no difference in height, weight, and BMI between subjects and a control group of healthy age-matched 1411 men and
Results
A total of 343 healthy adults aged 22–94 y were recruited as subjects. Table I shows the anthropometric and BIA characteristics of healthy men and women grouped by age. Older subjects were progressively shorter than the younger ones. Weights increased with age in men and women until 59 y and thereafter decreased. Resistance decreased with age in both sexes until 59 y and then increased with age. Reactance decreased progressively in men and women after 60 y. H2/R also increased until age 59 y
Discussion
BIA has been developed for field use and has shown great potential for use in estimating body composition and it is easy, non-invasive, and inexpensive. BIA measures the conductivity of total body water and electrolytes that are found only in FFM with an applied radiofrequency electrical current. Both total body water and electrolytes have been shown to be highly correlated with FFM.4, 29 DXA is considered one of the reference methods for measuring FFM.30 Our data provide measured (DXA) and
Conclusion
The results of this study show that the new Geneva BIA equation, validated against DXA, can be used to predict FFM in subjects aged 20–94 y and with BMIs from 17.0 to 33.8 kg/m2. Furthermore, the results of this study suggest that reactance appears to be essential for BIA equations developed for use in populations with large variations in age and body mass or for subjects where FFM decrease with age, i.e., those older than 60 y.
Acknowledgements
The authors are indebted to Giulio Conicella and to Luc Terraneo for technical assistance. The authors thank the Foundation Nutrition 2000Plus for its financial support.
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This study was supported by Foundation Nutrition 2000Plus.