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19001717 What is BMI?
Body Mass Index (BMI) is a simple measurement used to evaluate an individual’s weight status by comparing their weight to their height. This tool is widely used by healthcare professionals to provide a general overview of whether an individual is underweight, overweight, or obese, helping to guide dietary and exercise recommendations.
A BMI outside the healthy weight range may increase the risk of certain health conditions. For instance, individuals with a BMI in the obese category are at higher risk for type 2 diabetes, cardiovascular diseases, cancer, and other health issues.
However, BMI has limitations, as it does not directly measure body fat mass. It may not be accurate for people with a higher muscle mass, such as athletes, or older adults with muscle loss. It is important to consider BMI alongside other factors such as medical tests, physical exams, and lifestyle habits.
How to calculate BMI?
The BMI formula is as follows:
BMI = weight (kg) / (height (m))²
For example, if an individual weighs 55 kg and is 1.75 meters tall, the BMI would be:
BMI = 55 / (1.75)² = 17.96
BMI helps determine if a person is underweight, overweight, or obese, but it does not provide information on where body fat is distributed. To assess fat distribution, the Waist-Hip Ratio (WHR) can be used. The WHR compares the circumference of the waist to the circumference of the hips and is used to evaluate fat distribution across the body. This ratio can help better assess health risks based on whether fat is concentrated around the abdomen or hips.
For example, someone with a normal BMI but a high WHR may be at increased risk for heart disease or diabetes due to abdominal fat accumulation. The formula for WHR is:
WHR = waist circumference (cm) / hip circumference (cm)
Classification of BMI levels
BMI classifications for adults and children have key differences. For adults (over 20 years), the BMI formula is the same for both males and females and does not vary with age. However, for children and adolescents, BMI needs to be assessed differently due to uneven growth stages.
BMI classification for adults
Below is the BMI classification according to the World Health Organization (WHO) and the International Diabetes Federation (IDI & WPRO), to help assess body status:
| Classification | BMI (WHO) kg/m² |
| Severe thinness | < 16 |
| Thinness | 16 – 16.9 |
| Underweight | 17 – 18.4 |
| Normal | 18.5 – 24.9 |
| Pre-obesity | 25 – 29.9 |
| Class 1 obesity | 30 – 34.9 |
| Class 2 obesity | 35 – 39.9 |
| Class 3 obesity | ≥ 40 |
*** Note: BMI is not recommended or should be used cautiously for the following groups:
- Athletes or individuals with high muscle mass
- Pregnant women
BMI classification for children
The BMI calculation for children is similar to that of adults but differs in the standards and classification system. For children, BMI needs to be assessed based on age and gender, as these standards change over time during development. The classification of BMI for children is done using age – and gender-specific charts developed by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC).
BMI classification in children is intended for screening purposes, not diagnosis. A comprehensive assessment should include growth patterns, nutrition, and physical activity levels.
Conclusion
BMI is a simple yet effective tool for evaluating weight status and overall health. However, it should not be the sole measure of health. To achieve a healthy body and avoid health risks, BMI should be considered alongside other testing methods, a balanced diet, and regular exercise.
