To analyse the association between waist-to-height ratio (WtHR) and body fat and to develop predictive adiposity equations that will simplify the diagnosis of obesity in the paediatric age group.

Cross-sectional study conducted in Spain during 2007 and 2008. Anthropometric dimensions were taken according to the International Biology Program. The children were classified as underweight, normal weight, overweight or obese according to national standards of percentage body fat (%BF). WtHR differences among nutritional status categories were evaluated using ANOVA. Correlation analysis and regression analysis were carried out using WtHR as a predictor variable for %BF. A t test was applied to the results obtained by the regression model and by the Siri equation. The degree of agreement between both methods was evaluated by estimating the intra-class correlation coefficient.

Elementary and secondary schools in Madrid (Spain).

Girls (n 1158) and boys (n 1161) from 6 to 14 years old.

WtHR differed significantly (P < 0·001) depending on nutritional status category. This index was correlated (P < 0·001) with all adiposity indicators. The mean %BF values estimated by the regression model (boys: %BF = 106·50 × WtHR – 28·36; girls: %BF = 89·73 × WtHR – 15·40) did not differ from those obtained by the Siri equation. The intra-class correlation coefficient (0·85 in boys, 0·79 in girls) showed a high degree of concordance between both methods.

WtHR proved to be an effective method for predicting relative adiposity in 6–14-year-olds. The developed equations can help to simplify the diagnosis of obesity in schoolchildren.