Body Mass Index (BMI)

Obesity is not a current observable fact and can be described as a disproportionate accumulation of body fat, which brings on severe health risks. Very much a part of a group of diseases called "complex diseases", being overweight reflects the multi-factorial effect of all contributing genes as well as environmental factors.

Classification of obesity according to BMI

The primary categorization of obesity is based on an individual’s Body Mass Index which is so designed that it can relate Body Mass Index to the impending risk of diseases. The relationship between BMI and disease risk tends to vary among individuals as well as among different population groups as Body Mass Index readings denote relative risk and not absolute risk. Absolute risk is determined by a summation of risk factors. Therefore, it is essential that this classification be viewed as a broad generalization.

Individuals who have a muscular physique may have a Body Mass Index which places them in the overweight category, but in actual fact they are not overly fat. In addition, short people under 5 feet may have high BMIs that do not correctly reflect overweight or fatness. Moreover, receptiveness to risk factors at a given weight also tends to vary amongst individuals like multiple risk factors with mild overweight or fewer risk factors with severe overweight.

No randomized controlled trial studies exist that may lend credence to a specific system for classification that could establish the degree of risk in patients even during weight loss or weight maintenance. Therefore, it would not be wrong to mention that this classification is based purely on observational and prospective epidemiological studies.

How is BMI calculated?

The Body Mass Index helps in the classification of overweight and an estimation of relative risk for disease as compared to normal weight. Calculating Body Mass Index is simple, rapid, and inexpensive. The classification is applied to adults in whom Body Mass Index is a more direct presentation to risk of morbidity and mortality, increasing in a graded fashion with increasing Body Mass Index in all population groups. Therefore, absolute risk in obese and non-obese persons depends on the summed contribution of major risk factors.

In addition, it is essential that clinical judgment be used to interpret Body Mass Index in situations where it may not be an accurate indicator of total body fat like in presence of edema, high muscularity, muscle wasting, or in very short people. The relationship between Body Mass Index and body fat content also differs with age, sex, and possibly ethnicity which are further dependent on lean tissue, sitting height, and hydration state. Broadly generalized, a BMI chart should be understood as mentioned below:

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