Understanding Body Mass Index (BMI) & Body Composition
Body Mass Index (BMI) is an internationally recognized anthropometric screening metric established by the World Health Organization (WHO) to classify individuals into distinct weight categories correlating with potential health outcomes.
1. BMI Formulas (Metric & Imperial)
BMI calculates the relationship between body weight and stature:
\text{Metric:} \quad \text{BMI} = \frac{\text{Weight (kg)}}{[\text{Height (m)}]^2} \\[8pt]
\text{Imperial:} \quad \text{BMI} = 703 \times \frac{\text{Weight (lbs)}}{[\text{Height (inches)}]^2}
2. WHO International BMI Classification Table
| Category | BMI Range ($kg/m^2$) | BMI Prime | Health Risk Profile |
|---|---|---|---|
| Underweight | < 18.5 | < 0.74 | Nutritional deficiency, osteoporosis |
| Normal Weight | 18.5 – 24.9 | 0.74 – 1.00 | Lowest cardiovascular disease risk |
| Overweight | 25.0 – 29.9 | 1.00 – 1.20 | Moderate risk of hypertension & Type 2 diabetes |
| Obese (Class I) | 30.0 – 34.9 | 1.20 – 1.40 | High metabolic & joint stress risk |
| Obese (Class II & III) | ≥ 35.0 | ≥ 1.40 | Very severe chronic disease risks |
3. What is BMI Prime?
BMI Prime is the ratio of an individual's actual BMI to the upper limit of normal BMI ($25.0\text{ kg/m}^2$): $\text{BMI Prime} = \frac{\text{BMI}}{25}$. A BMI Prime under $1.0$ indicates normal or lower body weight, while values above $1.0$ quantify the exact percentage excess weight above the clinical upper boundary (e.g. a BMI Prime of $1.15$ means 15% above optimal weight).