What is the Body Mass Index?

What is the Body Mass Index?

Body mass index (BMI) is a simple screening tool used to classify weight categories in adults. It is calculated by dividing body weight in kilograms by height in meters squared.

Body Mass Index (BMI) = weight (kg) / height (m²)

BMI does not directly measure body fat or overall health, but it is widely used because it is easy to calculate and has been shown to correlate with the risk of health complications and overall mortality at a population level.

Obesity is commonly defined as a BMI of 30 kg/m² or higher, while overweight is defined as a BMI between 25 and 29.9 kg/m². However, a higher BMI does not always indicate excess body fat, particularly when increased weight is due to greater lean (muscle) mass.

The distribution of body fat is also important for health risk assessment. Accumulation of fat within the abdomen (central or abdominal fat) is strongly associated with metabolic and cardiovascular disease risk. This can be assessed using waist circumference (WC) measurements.

In adults, increased health risk related to abdominal fat is generally defined as:

• Waist circumference ≥ 94 cm in men
• Waist circumference ≥ 80 cm in non-pregnant women

These cut-off values may vary according to ethnic background. For example, people of Asian descent may develop obesity-related health complications at lower BMI and waist circumference values.

BMI and waist circumference are therefore used together as part of a comprehensive medical assessment of obesity as a chronic disease.

Table 1: Obesity classification according to body mass index (BMI). T2DM: Type 2 diabetes mellitus.