What Is BMI and How to Read the Classification Table?
The Body Mass Index (BMI) is a widely used public health indicator that assesses whether a person's body weight falls within a healthy range relative to their height. Originally proposed by Belgian mathematician Adolphe Quetelet in the 19th century and later adopted by the World Health Organization (WHO), BMI is calculated by dividing body weight in kilograms by the square of height in meters.
Why Use the BMI Table?
The BMI table provides a quick reference to understand which weight range you fall into. Although it is a population-level indicator — developed primarily for analyzing large groups rather than individuals — it remains widely used in clinical screenings, epidemiological research, and public health programs worldwide.
When consulting the table, it is important to remember that BMI does not distinguish between muscle mass and body fat, does not account for fat distribution, ethnicity, or specific health conditions. It should always be interpreted alongside other clinical data by a health professional.
BMI Ranges: What They Mean in Practice
Underweight (BMI below 18.5): Indicates body weight below recommended levels. May be associated with malnutrition, nutritional deficiencies, bone fragility, or eating disorders. A very low BMI is not automatically healthy.
Normal Weight (BMI 18.5 – 24.9): Range associated with the lowest risk of chronic diseases. Population studies consistently show that individuals in this range tend to have better life expectancy, especially when combined with regular physical activity and balanced nutrition.
Overweight (BMI 25.0 – 29.9): Increased risk for type 2 diabetes, hypertension, and cardiovascular disease. In highly muscular individuals (athletes, bodybuilders), a BMI in this range may not reflect excess body fat — additional assessments are recommended.
Obesity Classes I, II, and III: Progressively more serious, with increasing risk of metabolic syndrome, cardiovascular disease, sleep apnea, joint problems, and certain cancers. From Class II onward, specialized medical follow-up is strongly recommended.
Limitations of BMI: What the Table Does Not Show
The main criticism of using BMI as the sole health indicator is that it does not differentiate fat from muscle. A highly muscular person may show a BMI in the overweight range despite having a low body fat percentage. Conversely, someone with a normal BMI may have high body fat (known as "normal-weight obesity" or skinny fat).
Complementary indicators include waist circumference (men: increased risk above 94 cm; women: above 80 cm), body fat percentage (measured via bioimpedance or DEXA), and waist-to-hip ratio.
BMI and Specific Populations
The standard WHO classification was developed primarily based on European populations. For Asian populations, research suggests that metabolic risks increase at lower BMI thresholds (overweight: above 23 kg/m²; obesity: above 27.5 kg/m²). For adults aged 60 and over, the standard WHO classification is no longer the most appropriate. Due to natural losses in bone and muscle mass that accompany aging, different cut-off points apply. Consult our BMI table for elderly men or BMI table for elderly women based on the Lipschitz (1994) classification.
📚 Scientific Sources & References
- World Health Organization. Physical status: the use and interpretation of anthropometry. WHO Technical Report Series, No. 854. Geneva: WHO, 1995.
- World Health Organization. Obesity: preventing and managing the global epidemic. WHO Technical Report Series, No. 894. Geneva: WHO, 2000.
- Keys A, et al. Indices of relative weight and obesity. J Chronic Dis. 1972;25(6-7):329-343.
- Deurenberg P, et al. Body mass index as a measure of body fatness. Br J Nutr. 1991;65(2):105-114.
- Flegal KM, et al. Association of all-cause mortality with overweight and obesity. JAMA. 2013;309(1):71-82.