1. BMI formula
BMI = weight (kg) / height (m)²
Same formula worldwide. The interpretation (cutoffs) is what differs by population.
2. Korean / Asia-Pacific adult cutoffs (KSSO 2022)
| Category | BMI (kg/m²) |
|---|---|
| Underweight · 저체중 | < 18.5 |
| Normal · 정상 | 18.5 – 22.9 |
| Overweight (pre-obese) · 과체중 | 23.0 – 24.9 |
| Obesity Class I · 1단계 비만 | 25.0 – 29.9 |
| Obesity Class II · 2단계 비만 | 30.0 – 34.9 |
| Obesity Class III · 3단계 비만 | ≥ 35.0 |
3. Why lower than WHO?
The WHO Expert Consultation (Lancet 2004) documented that East and South Asian populations accumulate cardiometabolic risk at lower BMI than Caucasian populations — more visceral fat relative to total weight, more type 2 diabetes at BMI 23–25. The Korean Society for the Study of Obesity adopted 23 as the overweight threshold and 25 as the obesity threshold (vs WHO's 25 and 30).
4. Waist circumference (abdominal obesity)
BMI ignores fat distribution. KSSO 2022 defines abdominal obesity at ≥ 90 cm (men) and ≥ 85 cm (women) — lower than the IDF global threshold — because Koreans have more visceral fat per unit waist.
5. Pediatric BMI (ages 2–19)
For children, BMI varies with age and sex, so absolute cutoffs do not work. The KDCA 2017 Korean National Growth Charts provide BMI-for-age percentiles (LMS method). We report:
- Underweight: < 5th percentile
- Normal: 5th – 84th percentile
- Overweight: 85th – 94th percentile
- Obesity: ≥ 95th percentile (or ≥ adult 25 cutoff)
- Severe obesity: ≥ 1.2 × P95
6. Box-Cox LMS method
Z = ((BMI / M)^L − 1) / (L × S) Percentile = Φ(Z) × 100
Where L, M, S are sex- and age-specific parameters. Our table interpolates the published KDCA 2017 LMS values between integer ages.
7. Limits of BMI
- Muscular athletes often classify as overweight/obese despite low body fat.
- Older adults lose muscle mass; low BMI (< 21) is associated with higher mortality.
- Pregnancy, edema, and large lean mass distort BMI.
- Use body-fat % and waist circumference as complementary metrics.
8. References
- Korean Society for the Study of Obesity. 2022 Clinical Practice Guidelines for Obesity.
- WHO Expert Consultation. Lancet 2004;363:157–163.
- Korea Disease Control and Prevention Agency. 2017 Korean National Growth Charts for Children and Adolescents.
- Cole TJ. The LMS method for constructing normalized growth standards. Eur J Clin Nutr 1990.