MON-696 - Establishing Age- and Sex-Specific Body Fat Percentage and Body Mass Index Cutoffs for Obesity Diagnosis in Korean Children and Adolescents

Objective
This study aimed to define age- and sex-specific thresholds for obesity in Korean children and adolescents using body fat percentage as a reference standard. In addition, we aimed to compare these newly derived thresholds with currently used criteria and to evaluate the diagnostic performance of body mass index–based measures.

Study Design
Data comprising 520,482 measurements (268,878 from males and 251,604 from females) obtained from 96,600 individuals aged 7 to 15 years were analyzed. Using population-specific L, M, and S parameters for Korean children and adolescents, body fat percentage cutoffs were determined based on standard deviation scores projected to age 16, corresponding to 25% in males and 35% in females. Based on these body fat percentage reference points, revised body mass index cutoffs were subsequently generated to improve diagnostic sensitivity. The performance of the proposed cutoffs was then systematically compared with existing standards.

Results
Age- and sex-specific obesity thresholds based on both body fat percentage and body mass index were established at monthly age intervals. The proposed body fat percentage cutoffs, which reflect both clinically relevant fat levels and age-related distribution patterns, yielded a relatively uniform obesity prevalence of approximately 20% across age groups. Compared with conventional body mass index criteria, the revised body mass index cutoffs showed superior sensitivity and a significantly larger area under the receiver operating characteristic curve in both sexes. These improvements were achieved while reducing false-negative classifications and markedly lowering false-positive rates. Notably, among boys aged 9 to 12 years—an interval characterized by rapid linear growth and increases in skeletal muscle mass—the updated body mass index criteria effectively mitigated obesity overdiagnosis in individuals with relatively low body fat percentage, a limitation frequently observed with prior standards.

Conclusions
This study proposes new age- and sex-specific body fat percentage and body mass index cutoffs that more accurately reflect the unique body composition patterns of Korean children and adolescents. The findings underscore important shortcomings of existing body mass index–based definitions, particularly their propensity to overestimate obesity during early pubertal development in boys. By incorporating physiologic variations related to age and sex, the newly developed criteria offer improved diagnostic accuracy and support earlier identification of obesity, facilitating timely intervention and individualized management strategies.

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