The Cut Off Value of Body Fat Percentage for Diagnosing Obesity Among Selected Number of Elementary School Students in Seoul

Hwang, In Cheol; Kim, Kyoung Kon; Suh, Dong Hoon; Lee, Kyu Rae

Abstract

BACKGROUND
Measurement of body fat amount is necessary in assessment of obese people. Bioelectric impedance analysis (BIA) is an indirect method of measuring body fat amount, which has been widely applied in clinical and field settings because of its relatively low cost and non-invasive character. We tried to define the cut off values of body fat amount measured by BIA method which would correspond to those of body mass index (BMI) in order to detect overweight and obesity in children of this trial.
METHODS
By using the BIA method, measurements of height, weight and body fat percentage of 1321 sixth-grade students (aged 10~12 years) were taken from eight different elementary schools located in Seodaemun-gu, Seoul, Korea. The student's BMI percentiles for their age and gender were determined based on the Korean pediatrics society growth chart established in 2007, then they were categorized into three groups; normal, overweight and obese. The cut off values of body fat percentage, which would correspond to those of BMI percentiles were calculated by ROC curve analysis.
RESULTS
Among 1286 subjects, 35 were excluded due to mechanical malfunction. The mean body fat percentage was 18.5 +/- 2.1% in normal group, 23.6 +/- 1.1% in overweight group and 27.2 +/- 2.1% in obese group. For classification of overweight, the correspondent cut off value of body fat percentage was 29% in boys and 26% in girls. For obesity, the cut off value was 31% for both boys and girls. The kappa values for the agreement between BMI percentiles criteria and body fat percentage cut off values were 0.5974 in boys and 0.6056 in girls (P < 0.001).
CONCLUSION
According to the criteria suggested by the Korean pediatrics society in 2007, the most appropriate cut off values of body fat percentage in 10~12 years old children were 29% for overweight and 31% for obesity in boys, and 26% for overweight and 31% for obesity in girls, respectively.