What is Body Mass Index? Why is BMI used to measure if a person is overweight or obese?

Every time you visit a hospital for a routine check-up, you are made to step on a weighing scale as a nurse or doctor jots down your weight. It will be used to check your Body Mass Index (BMI).

What is BMI?
For over 100 years, medical professionals have used BMI to determine a person's weight category. It uses a mathematical formula by combining the weight and height of an individual to find out if s/he is underweight or overweight.


Formula: BMI = weight (kg) / height²
BMI is calculated by dividing weight (in kilograms) by the square of height (in meters).

Why do people use BMI to calculate obesity?
Also known as an obesity indicator, BMI helps health experts and professionals determine if a patient is overweight or underweight.

Dr Sneha Kothari, Consultant - Endocrinology at Global Hospitals Mumbai, said that the BMI cut-offs are different for Indians.

“While people with BMI between 23 and 24.9 are considered overweight, those with BMI more than 25.0 come under the obese category. People with BMI between 18.5 and 23 are believed to have a healthy weight,” she informed.

However, the tool has attracted some criticism for causing confusion and failing to measure the abdominal/waist fat while determining obesity.

Many doctors and health experts say the system isn't conclusive as it doesn't accurately measure a person’s health. Hence, it cannot be assumed that a person with normal BMI is healthy, or an individual who has high BMI is unhealthy.

Limited or lack of physical activity, poor eating habits and lack of sleep have resulted in more people getting lifestyle diseases like diabetes, hypertension and obesity, among others.

People with such comorbidities are most vulnerable to Covid-19. BMI can be used to generally follow fitness goals, but should not be the only parameter.