Waist-to-Height Ratio Standards Based on Agreement With Health-Related Body Fat

Background/Purpose: FITNESSGRAM uses percent body fat (%BF) or body mass index (BMI) to assess body composition in school-aged children. However, waist-to-height ratio (WHtR) has emerged from the literature as an easy to use index that has demonstrated ability to accurately distinguish children with risk factors associated with cardio-metabolic diseases. The purpose of this study was to determine thresholds for WHtR that could be used to identify FITNESSGRAM’s body composition Fitness Zone classification based on %BF, which has shown previously to associate with health-related outcomes in school-aged children. Method: WHtR and %BF were obtained from 134 middle-school students (69 girls, 65 boys) recruited from three private schools from a metropolitan area located in the southwestern US. Waist circumference (WC) was obtained by averaging three circumference measurements at the level of the superior border of the iliac crest, rounded to the nearest 1 cm. WHtR was calculated dividing WC by height (in cm). Percent body fat was obtained using the hand-held Omron HBF-301 BIA device. To ensure testing consistency, a trained graduate student collected both WC (WHtR) and %BF during each student’s physical education class.  Analysis/Results:  Separate receiver-operating characteristic (ROC) curves were used to determine optimal gender-specific WHtR cutoffs based on agreement with FITNESSGRAM’s %BF standards. Area under the curve (AUC), sensitivity (Se), and specificity (Sp) values from ROC curve analyses were reported for each gender group. For girls, the optimal WHtR threshold for discriminating students classified into either the Healthy Fitness Zone or Needs Improvement Zone was found to be 0.4310 (AUC=.9038; Se=84.62%, Sp=85.71%), for boys the optimal threshold was .4243 (AUC=0.7437; Se=71.43%, Sp=72.55%). AUC values for both ROC curves were statistically significant (P<.05).  Conclusions: A WHtR of 0.42-0.43 may serve as a cut-off for middle-school children who have unfavorable accumulation of central adiposity associating with health risk. The results indicate that WHtR was a strong discriminator of children classified into FITNESSGRAM’s body composition Fitness Zones in middle-school girls. Weaker diagnostic capabilities were found in boys, suggesting that WHtR may have stronger utility as an alternative body composition screening measure for identifying cardio-metabolic risk in girls of this age group.