title: Childhood body composition in relation to body mass index.
abstract: OBJECTIVE
  The aim is to describe body composition in relation to body mass index (BMI; body weight/stature(2)) to provide health care professionals insight into the meaning, significance, and limitations of BMI as an index of adiposity during childhood.
  
  
  METHODS
  Data from 387 healthy, white children 8 to 18 years of age from the Fels Longitudinal Study were analyzed. Measurements were scheduled annually and each child was examined 1 to 11 times, totaling 1748 observations. Total body fat (TBF) and fat-free mass (FFM) were determined from hydrodensitometry. Stature and weight were measured using standard methods and BMI and the components of BMI, TBF/stature(2), and FFM/stature(2) were calculated. Analyses included correlations between BMI and body composition variables; age-related patterns of BMI, TBF/stature(2), and FFM/stature(2); and annual changes in BMI, TBF/stature(2), and FFM/stature(2).
  
  
  RESULTS
  Generally, correlations between BMI and body composition variables were strong and significantly different from zero. Means for BMI throughout childhood were similar for boys and girls, although significantly larger values were observed for girls at ages 12 to 13 years. Age-related patterns of TBF/stature(2) and FFM/stature(2) differed between sexes. In each sex, annual increases in BMI were driven primarily by increases in FFM/stature(2) until late adolescence, with increases in TBF/stature(2) contributing to a larger proportion of the BMI increases in girls than in boys.
  
  
  CONCLUSIONS
  Unlike adults, annual increases in BMI during childhood are generally attributed to the lean rather than to the fat component of BMI. Because the properties of BMI vary during childhood, health care professionals must consider factors such as age and sex when interpreting BMI.
authors.affiliation: Division of Human Biology, Department of Community Health, Wright State University School of Medicine, Kettering, Ohio 45420-4014, USA. leah.maynard@wright.edu
authors.forename: L M
authors.initials: LM
authors.lastname: Maynard
authors.forename: W
authors.initials: W
authors.lastname: Wisemandle
authors.forename: A F
authors.initials: AF
authors.lastname: Roche
authors.forename: W C
authors.initials: WC
authors.lastname: Chumlea
authors.forename: S S
authors.initials: SS
authors.lastname: Guo
authors.forename: R M
authors.initials: RM
authors.lastname: Siervogel
mesh_terms: D000273:Adipose Tissue; D000293:Adolescent; D001823:Body Composition; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D012016:Reference Values; D012727:Sex Characteristics