Obesity is rapidly spreading across all regions and demographic groups around the world, with the World Health Organization (WHO) estimating more than 1.6 billion people worldwide are overweight and at least 300 million of these are obese.

Obesity is a clinical condition in which there is in an excess of total body fat, which results from caloric intake exceeding energy usage. Body mass index (BMI) and waist circumference are the two main measures used for monitoring body weight.

WHO has defined obesity into categories according to the body mass index (BMI) (Table 1). Individual BMI is an acceptable measure of total body fat that is widely used to estimate the relative risk of disease, however, it may not be suitable for all ethnic groups (e.g. Asians, as they may have equivalent levels of risk at lower BMI, and Polynesians, as they may have equivalent levels of risk at higher BMI) and is also unsuitable for children.

Table 1. Classification of adult underweight, overweight and obesity according to BMI and risk of obesity-related comorbidities

Source: World Health Organization - Global Database on BMI.

The waist circumference is another measure used to identify overweight individuals at increased risk of obesity-related conditions due to excess fat in the abdominal region (Table 2). Generally, a waist circumference of 94 cm or more in males and 80 cm or more in females indicates increased risk, whereas a waist circumference of 102 cm or more in males and 88 cm or more in females indicates substantially increased risk. Similar to the BMI classification, the waist circumference classification is not suitable for all ethnic groups and those aged less than 18 years.

Table 2. Waist circumference risk

The term ‘morbid obesity’ refers to BMI ≥ 40 kg/m2, or BMI ≥ 35 kg/m2 with at least one significant comorbidity such as type 2 diabetes.