Validity of impedance-based equations for the prediction of total body water as measured by deuterium dilution in African women

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 populationspecific, 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 (1.3-1.9 kg) in all cases, whereas a large range of bias (0.2-6.1 kg) was observed independently of the ethnic origin of the sample from which the equations were derived. Three equations (2 from whites and 1 from 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.Am J Clin Nutr 2005;81:597-604.

Use of bioelectrical impedance analysis to assess body composition in rural Gambian children

“…We found that height, weight, impedance, sex and age produced the most effective prediction of %FFM with an R 2 of 0.81. This closely agrees with novel equations developed for a hand-to-hand impedance system in a group of West African women (R 2 ¼ 0.82), when the manufacturer's equations were also found to be biased (Dioum et al, 2005a). In our study, the addition of skinfold thickness measurements into the final equation improved the ability even further with an adjusted R 2 of 0.84, even though fat-free tissue is not directly an output associated with skinfold thickness.…”

Body composition measures of obese adolescents by the deuterium oxide dilution method and by bioelectrical impedance

“…Immediately after the anthropometric exams and BIA, saliva was collected from the subjects and deuterium oxide was offered to them. This permitted the exams to be performed at the same time and under the same conditions, with a consequent constant state of hydration during all methods of body assessment used in the study (18).…”

“…It is evident from recent studies that the use of BIA for the assessment of body composition in children requires specific prediction formulas differing from those established for adults (12)(13)(14). Such formulas have been developed for the prediction of FFM (15)(16)(17)(18)(19) and of TBW (12)(13)(14) in children. BIA could also be an easily applicable method for the assessment of body composition in obese children, but until now it has not been validated for this population.…”

Assessment of adiposity by bio impedance analysis: developing a population specific equation for Sri Lankan adolescents

“…The inclusion of BMI in the equation indicates that it is a valuable component in body fat assessment, though on its own it may be prone to error. Though previous BIA equations too included height 2 / resistance as a prediction variable (14-16), body weight and age, which are common variables in other prediction equations (10), body weight may have been eliminated due to the inclusion of BMI into our equation and age, due to the narrow age range of our study population.…”

“…There are no published BIA equations for South Asian adolescents, with the few available equations being derived for the prediction of total body water (TBW), and through it, fat mass (7)(8)(9). Ideally, the available %FM prediction equations should be validated in the population being assessed prior to use, or population specific prediction equations should be derived against a reference method to improve accuracy of BIA analysis (10).…”