There are several standardized types of obesity that have been classified by the World Health Organization (WHO), ranging from class I to class III, but have since been subdivided by other organizations into categories such as “mild obesity” and “super obesity” to provide a frame of reference. Since the WHO’s standards do not extend to these broken down categories, the exact body mass index (BMI) qualifications for each category may vary by as much as five points depending on the source. They can still, however, provide useful insight into the severity of each of the types of obesity.
The types of obesity set by the WHO were classified based on BMI, a method that measures whether a person’s weight is appropriate for his or her height by taking the person’s weight in kilograms and dividing by the square of his or her height in meters. It is important to note that, while BMI is significantly correlated with the amount of body fat a person has, it does not take into account body type, and may not perfectly reflect a person’s health risks in certain circumstances. For instance, a heavily muscled, fit individual may have a BMI that is considered obese even without an excess of body fat.
A normal BMI falls in the range of 18.5 to 24.99. People who have BMIs of 25 to 29.99 are considered overweight, or “pre-obese.” While this is not technically obesity, individuals in this category should exercise caution and try to prevent any further weight gain, as this stage is associated with the beginnings of obesity-related illnesses. For some people, an underlying illness may be causing the excess weight. It is important to obtain a diagnosis and treatment for such illnesses in this stage before they cause the individual to progress into full obesity.
Class I is the first and lowest of the true types of obesity. Individuals with a BMI between 30 and 34.99 would fall into this category. Class II includes BMIs of 35 to 39.99. Class III, or a BMI of over 40, includes the sub-categories of severe, morbid, and super obesity, in order of increasing severity.
Though even mild obesity presents considerable health risks, class III has the highest incidence of health problems related to obesity. The excess body fat and the sedentary lifestyle that often accompanies it can lead to a number of diseases including hypertension, high cholesterol, and diabetes. Very obese individuals are also at a higher risk for sleep apnea, liver disease, and some types of cancer.