title: BMI was right all along: taller children really are fatter (implications of making childhood BMI independent of height) EarlyBird 48.
abstract: OBJECTIVE
  Several studies suggest that taller children may be wrongly labelled as 'overweight' because body mass index (BMI) is not independent of height (Ht) in childhood, and recommend adjustment to render the index Ht independent. We used objective measures of %body fat and hormonal/metabolic markers of fatness to investigate whether BMI and the corresponding fat mass index (FMI) mislead in childhood, or whether taller children really are fatter.
  
  
  METHODS
  Longitudinal observational study measuring children annually from age 7 to 12 years.
  
  
  METHODS
  Two hundred and eighty healthy children (56% boys) from the EarlyBird study.
  
  
  METHODS
  BMI (body mass (BM)/Ht(2)), FMI (fat mass (FM)/Ht(2)), %body fat ((FM/BM) × 100, where FM was measured by dual-energy X-ray absorptiometry), fasting leptin (a hormonal measure of body fatness) and insulin resistance (a metabolic marker derived from the validated homeostasis model assessment program for insulin resistance--HOMA2-IR) were all analysed in relation to Ht. Alternative Ht-independent indices of BM and FM were compared with BMI and FMI as indicators of true fatness and related health risk.
  
  
  RESULTS
  BMI and FMI correlated with Ht at each annual time point (r~0.47 and 0.46, respectively), yet these correlations were similar in strength to those between Ht and %fat (r~0.47), leptin (r~0.41) and insulin resistance (r~0.40). Also, children who grew the most between 7 and 12 years showed greater increases in BMI, FMI, leptin and insulin resistance (tertile 1 vs 3, all p<0.05). BMI and FMI explained ~20% more of the variation in %fat, ~15% more in leptin and ~10% more in insulin resistance than the respective Ht-independent reformulations (BM/Ht(3.5) and FM/Ht(7), both p<0.001).
  
  
  CONCLUSIONS
  Taller children really are fatter than their shorter peers, have higher leptin levels and are more insulin resistant. Attempts to render indices of BM or FM independent of Ht in children seem inappropriate if the object of the index is to convey health risk.
authors.affiliation: Department of Endocrinology and Metabolism, Peninsula College of Medicine and Dentistry, Plymouth Campus, Plymouth, UK. brad.metcalf@phnt.swest.nhs.uk
authors.forename: B S
authors.initials: BS
authors.lastname: Metcalf
authors.forename: J
authors.initials: J
authors.lastname: Hosking
authors.forename: A E
authors.initials: AE
authors.lastname: Frémeaux
authors.forename: A N
authors.initials: AN
authors.lastname: Jeffery
authors.forename: L D
authors.initials: LD
authors.lastname: Voss
authors.forename: T J
authors.initials: TJ
authors.lastname: Wilkin
mesh_terms: D015502:Absorptiometry, Photon; D001823:Body Composition; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D003627:Data Interpretation, Statistical; D005215:Fasting / Q000378:metabolism; D005260:Female; D006801:Humans; D007333:Insulin Resistance; D020738:Leptin / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D009765:Obesity / Q000145:classification / Q000175:diagnosis* / Q000378:metabolism
chemical_list: D020738:Leptin