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What is Body Mass Index (BMI)?

Obesity can be quantitatively measured using Body Mass Index (BMI). Body Mass Index is widely regarded as the measure of health in a person. It is also known as Quetelet index. Weight in kilograms divided by the square of the height in meters shall give the BMI of a person.

The World Health Organization classifies individuals into the underweight, normal weight and overweight categories on the basis of their BMI values.

BMI of a healthy person ranges from 18.5 to 24.99. Any value less than 18 is considered to be underweight. Overweight persons are those whose BMI values are more than 25. A BMI value between 25 and 29.99 refers to the condition of pre-obesity.

Obese individuals have a BMI greater than 30. 3 sub-classes of obesity exist. A BMI range 30-34.99 is considered to be of class 1 obesity. Class 2 obesity lies between 35 and 39.99. The most severe form of obesity is class 3 obesity which has a BMI level of over 40.

The main advantage of this index is that it is independent of age and gender. In addition, the results are also easy to comprehend. The procedure also does not require any kind of invasion like skin fold caliper testing.

However, there is one major drawback for this index. The body weight that is used to calculate BMI is an aggregate of bone & muscle mass, mass of internal organs, water content etc. It is possible for obtaining a high BMI despite of a low fat content. This might be due to a high muscle and bone weight. Therefore, BMI might give incorrect results for some individuals.

It is hence advisable to use BMI along with other tests like bi-electrical impedance, underwater weighing, skin fold caliper exam etc to have a more clear understanding about obesity.