Classifying the degree of obesity

An important early step in the assessment procedure is to measure the degree of obesity. While more sophisticated measures exist, in clinical practice the most common measurements are of body mass index (BMI) and waist circumference.

BMI

Body mass index is calculated by dividing the weight of an individual in kilograms by the height of that individual in metres squared.

The classifications for obesity are as follows¹:

There are limitations to the BMI measurement, for example, it does not distinguish between lean and fat tissue in the body.

It is not advisable to rely on self-reported measures of weight and height and it is good practice to include these measurements as part of any general medical assessment.

In measuring body weight it is vital to have a scale that can weigh all patients. Privacy is also very important and every care should be taken to ensure that this philosophy is in place within the practice. Patients should be asked to remove any outer garments such as coats, cardigans and their shoes, and to empty their pockets before stepping onto the scales. It is important for both patients and practitioners to feel confident in the reliability of body weight measurements and every effort should be made to perform this in a consistent and accurate manner.

To measure height, patients should be asked to stand straight with their back to the stadiometer and with the top of their head touching but not pressing against the rule. The arms should hang relaxed with the feet slightly apart.