title: Prediction of fat-free mass using bioelectrical impedance analysis in young adults from five populations of African origin.
abstract: OBJECTIVE
  Bioelectrical impedance analysis (BIA) is used in population and clinical studies as a technique for estimating body composition. Because of significant under-representation in existing literature, we sought to develop and validate predictive equation(s) for BIA for studies in populations of African origin.
  
  
  METHODS
  Among five cohorts of the Modeling the Epidemiologic Transition Study, height, weight, waist circumference and body composition, using isotope dilution, were measured in 362 adults, ages 25-45 with mean body mass indexes ranging from 24 to 32. BIA measures of resistance and reactance were measured using tetrapolar placement of electrodes and the same model of analyzer across sites (BIA 101Q, RJL Systems). Multiple linear regression analysis was used to develop equations for predicting fat-free mass (FFM), as measured by isotope dilution; covariates included sex, age, waist, reactance and height(2)/resistance, along with dummy variables for each site. Developed equations were then tested in a validation sample; FFM predicted by previously published equations were tested in the total sample.
  
  
  RESULTS
  A site-combined equation and site-specific equations were developed. The mean differences between FFM (reference) and FFM predicted by the study-derived equations were between 0.4 and 0.6 kg (that is, 1% difference between the actual and predicted FFM), and the measured and predicted values were highly correlated. The site-combined equation performed slightly better than the site-specific equations and the previously published equations.
  
  
  CONCLUSIONS
  Relatively small differences exist between BIA equations to estimate FFM, whether study-derived or published equations, although the site-combined equation performed slightly better than others. The study-derived equations provide an important tool for research in these understudied populations.
authors.affiliation: Department of Public Health Sciences, Stritch School of Medicine, Loyola University Chicago, Maywood, IL, USA. aluke@lumc.edu
authors.forename: A
authors.initials: A
authors.lastname: Luke
authors.forename: P
authors.initials: P
authors.lastname: Bovet
authors.forename: T E
authors.initials: TE
authors.lastname: Forrester
authors.forename: E V
authors.initials: EV
authors.lastname: Lambert
authors.forename: J
authors.initials: J
authors.lastname: Plange-Rhule
authors.forename: L R
authors.identifier: 0000000206928585
authors.initials: LR
authors.lastname: Dugas
authors.forename: R A
authors.initials: RA
authors.lastname: Durazo-Arvizu
authors.forename: J
authors.initials: J
authors.lastname: Kroff
authors.forename: W N
authors.initials: WN
authors.lastname: Richie
authors.forename: D A
authors.initials: DA
authors.lastname: Schoeller
mesh_terms: D000328:Adult; D044383:Black People; D001823:Body Composition; D015992:Body Mass Index; D001835:Body Weight; D015331:Cohort Studies; D017097:Electric Impedance; D005260:Female; D005869:Ghana; D006801:Humans; D007563:Jamaica; D008019:Life Style; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009752:Nutritional Status; D012750:Seychelles; D013019:South Africa; D014481:United States; D001741:Black or African American