【关键词】  impedance

    the Equipe de Nutrition, Laboratoire de Physiologie, Département de Biologie Animale, Faculté des Sciences et Techniques, Université Cheikh Anta Diop de Dakar, Sénégal, West Africa (AD, ASC, and SW)
    the Nutrition Unit, WHO Collaborating Centre for Nutrition, Institut de Recherche pour le Développement, Montpellier, France (AG, FD, and BM)
    the Institute of Physiology, Faculty of Medicine, University of Lausanne, Switzerland (YS).

    ABSTRACT

    Background: Little information is available on the validity of simple and indirect body-composition methods in non-Western populations. Equations for predicting body composition are population-specific, and body composition differs between blacks and whites.

    Objective: We tested the hypothesis that the validity of equations for predicting total body water (TBW) from bioelectrical impedance analysis measurements is likely to depend on the racial background of the group from which the equations were derived.

    Design: The hypothesis was tested by comparing, in 36 African women, TBW values measured by deuterium dilution with those predicted by 23 equations developed in white, African American, or African subjects. These cross-validations in our African sample were also compared, whenever possible, with results from other studies in black subjects.

    Results: Errors in predicting TBW showed acceptable values (1.31.9 kg) in all cases, whereas a large range of bias (0.26.1 kg) was observed independently of the ethnic origin of the sample from which the equations were derived. Three equations (2 from whites and 1 blacks) showed nonsignificant bias and could be used in Africans. In all other cases, we observed either an overestimation or underestimation of TBW with variable bias values, regardless of racial background, yielding no clear trend for validity as a function of ethnic origin.

    Conclusions: The findings of this cross-validation study emphasize the need for further fundamental research to explore the causes of the poor validity of TBW prediction equations across populations rather than the need to develop new prediction equations for use in Africa.

    Key Words: Bioelectrical impedance analysis  BIA equation  total body water prediction  validity  deuterium dilution  African women

    INTRODUCTION

    Water is the major chemical component of the body and is an essential medium of the body's internal environment. Total body water (TBW) is constantly maintained in healthy subjects, and it is frequently measured to evaluate body composition―a sensitive indicator of health and nutritional status. Simple methods are needed for epidemiologic field studies, notably in low-income countries; the most widely used method is bioelectrical impedance analysis (BIA) (1, 2). BIA is often used to estimate body fat and muscle, but it is important to recall that the conductor of the body is its water content, and a BIA analyzer actually measures the impedance of this fluid conductor, thus enabling assessment of