title: Validity of BMI as a measure of obesity in Australian white Caucasian and Australian Sri Lankan children.
abstract: BACKGROUND
  Body mass index (BMI) is used to diagnose obesity. However, its ability to predict the percentage fat mass (%FM) reliably is doubtful. Therefore validity of BMI as a diagnostic tool of obesity is questioned.
  
  
  OBJECTIVE
  This study is focused on determining the ability of BMI-based cut-off values in diagnosing obesity among Australian children of white Caucasian and Sri Lankan origin.
  
  
  METHODS
  Height and weight was measured and BMI (W/H2) calculated. Total body water was determined by deuterium dilution technique and fat free mass and hence fat mass derived using age- and gender-specific constants. A %FM of 30% for girls and 20% for boys was considered as the criterion cut-off level for obesity. BMI-based obesity cut-offs described by the International Obesity Task Force (IOTF), CDC/NCHS centile charts and BMI-Z were validated against the criterion method.
  
  
  RESULTS
  There were 96 white Caucasian and 42 Sri Lankan children. Of the white Caucasians, 19 (36%) girls and 29 (66%) boys, and of the Sri Lankans 7 (46%) girls and 16 (63%) boys, were obese based on %FM. The FM and BMI were closely associated in both Caucasians (r=0.81, P<0.001) and Sri Lankans (r=0.92, P<0.001). Percentage FM and BMI also had a lower but significant association. Obesity cut-off values recommended by IOTF failed to detect a single case of obesity in either group. However, NCHS and BMI-Z cut-offs detected cases of obesity with low sensitivity.
  
  
  CONCLUSIONS
  BMI is a poor indicator of percentage fat and the commonly used cut-off values were not sensitive enough to detect cases of childhood obesity in this study. In order to improve the diagnosis of obesity, either BMI cut-off values should be revised to increase the sensitivity or the possibility of using other indirect methods of estimating the %FM should be explored.
authors.affiliation: Children's Nutrition Research Centre, Department of Paediatrics and Child Health, University of Queensland, Brisbane, Australia.
authors.forename: V P
authors.initials: VP
authors.lastname: Wickramasinghe
authors.forename: G J
authors.initials: GJ
authors.lastname: Cleghorn
authors.forename: K A
authors.initials: KA
authors.lastname: Edmiston
authors.forename: A J
authors.initials: AJ
authors.lastname: Murphy
authors.forename: R A
authors.initials: RA
authors.lastname: Abbott
authors.forename: P S W
authors.initials: PS
authors.lastname: Davies
mesh_terms: D000293:Adolescent; D000465:Algorithms; D001315:Australia; D015415:Biomarkers; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000175:diagnosis* / Q000208:ethnology; D012680:Sensitivity and Specificity; D013188:Sri Lanka; D044465:White People
chemical_list: D015415:Biomarkers