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Morbid Obesity The Disease, Measurements & Classification

Obesity is a term that indicates excess body fat due to the increased size and number of adipose (fat) cells. It is now recognized that obesity is a disease associated with a significantly impaired quality of life and shortened life expectancy as a result of its close association with several other serious diseases. Overweight and obesity cause the development of diabetes, and contribute to high blood pressure, high cholesterol, infertility, birth complications and arthritis. The term ‘morbid’ refers to so-called ‘comorbid’ conditions which occur in association with morbid obesity.

The World Health Organization defines obesity according to body mass index (BMI).

BMI is calculated by dividing the person’s weight in kilograms by the square of his / her height in metres - (kg/m²).

The risk of developing life-shortening diseases associated with obesity increases exponentially as the BMI rises above 30. The classification of obesity is based on health risk groupings defined by levels of BMI:

Classification BMI (KG/m2) Risk
Underweight < 18.5 Increased
Normal 18.5 - 24.9 Normal
Overweight 25.0 - 29.9 Increased
Obese > 30 Rising Fast
I 30.0 - 34.9 High
II 30.0 - 39.9 Very High
III ≥ 40 Extremely High

The BMI is not the only factor determining health risk, however. Risk also depends upon where one carries the weight: those whose excess fat is distributed predominantly in and around the abdomen are at higher risk of serious cardiometabolic disease. The International Diabetes Federation uses waist circumferences of 94cm in men and 80cm in women as cut offs for increased risk.

In a large epidemiological study, Koster et al (• American Journal of Epidemiology Volume 167, Number 12 Pp. 1465-1475) showed that, compared with subjects with a combination of normal BMI (18.5–<25) and normal waist circumference, those in the normal-BMI group with a large waist circumference (men: 102 cm; women: 88 cm) had an approximately 20% higher mortality risk. The finding that persons with a normal BMI but a large waist circumference had a higher mortality risk in this study suggests that increased waist circumference should be considered a risk factor for mortality, in addition to BMI.