title: Are ethnic and gender specific equations needed to derive fat free mass from bioelectrical impedance in children of South asian, black african-Caribbean and white European origin? Results of the assessment of body composition in children study.
abstract: BACKGROUND
  Bioelectrical impedance analysis (BIA) is a potentially valuable method for assessing lean mass and body fat levels in children from different ethnic groups. We examined the need for ethnic- and gender-specific equations for estimating fat free mass (FFM) from BIA in children from different ethnic groups and examined their effects on the assessment of ethnic differences in body fat.
  
  
  METHODS
  Cross-sectional study of children aged 8-10 years in London Primary schools including 325 South Asians, 250 black African-Caribbeans and 289 white Europeans with measurements of height, weight and arm-leg impedance (Z; Bodystat 1500). Total body water was estimated from deuterium dilution and converted to FFM. Multilevel models were used to derive three types of equation {A: FFM = linear combination(height+weight+Z); B: FFM = linear combination(height(2)/Z); C: FFM = linear combination(height(2)/Z+weight)}.
  
  
  RESULTS
  Ethnicity and gender were important predictors of FFM and improved model fit in all equations. The models of best fit were ethnicity and gender specific versions of equation A, followed by equation C; these provided accurate assessments of ethnic differences in FFM and FM. In contrast, the use of generic equations led to underestimation of both the negative South Asian-white European FFM difference and the positive black African-Caribbean-white European FFM difference (by 0.53 kg and by 0.73 kg respectively for equation A). The use of generic equations underestimated the positive South Asian-white European difference in fat mass (FM) and overestimated the positive black African-Caribbean-white European difference in FM (by 4.7% and 10.1% respectively for equation A). Consistent results were observed when the equations were applied to a large external data set.
  
  
  CONCLUSIONS
  Ethnic- and gender-specific equations for predicting FFM from BIA provide better estimates of ethnic differences in FFM and FM in children, while generic equations can misrepresent these ethnic differences.
authors.affiliation: Division of Population Health Sciences and Education, St George's, University of London, London, United Kingdom.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Nightingale
authors.forename: Alicja R
authors.initials: AR
authors.lastname: Rudnicka
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Owen
authors.forename: Angela S
authors.initials: AS
authors.lastname: Donin
authors.forename: Sian L
authors.initials: SL
authors.lastname: Newton
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Furness
authors.forename: Emma L
authors.initials: EL
authors.lastname: Howard
authors.forename: Rachel D
authors.initials: RD
authors.lastname: Gillings
authors.forename: Jonathan C K
authors.initials: JC
authors.lastname: Wells
authors.forename: Derek G
authors.initials: DG
authors.lastname: Cook
authors.forename: Peter H
authors.initials: PH
authors.lastname: Whincup
mesh_terms: D050154:Adiposity; D001823:Body Composition; D002648:Child; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D005006:Ethnicity; D005260:Female; D006801:Humans; D008131:London; D008297:Male; D015233:Models, Statistical; D062486:Public Health Surveillance; D012737:Sex Factors