What is Involved in Making a Diagnosis of Obesity?

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  • Written By: Kelly Ferguson
  • Edited By: Heather Bailey
  • Last Modified Date: 27 September 2019
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According to the World Health Organization (WHO), the most common method for making a diagnosis of obesity is measuring the body mass index (BMI) of the individual. Other methods exist, including measuring the circumference of the waist to judge abdominal fat or taking a measurement of the individual’s body fat percentage, although there are several problems with using these methods. These problems include a lack of accuracy in making a diagnosis of obesity with the waist measurement and difficulty obtaining an accurate body fat percentage measurement without the benefit of expensive lab equipment. Additionally, the guidelines for a healthy body fat percentage differ based on age, gender, and ethnicity, making it harder to standardize a cutoff point for obesity. Most doctors use the guidelines set down by the WHO for determining obesity based on BMI.


An individual’s BMI is found by taking the body weight in kilograms and dividing it by the square of the height in meters. There is some variation in the qualifications for obesity depending on the source. The WHO, however, has attempted to standardize the cutoff point for a diagnosis of obesity at 30. In other words, an individual with a BMI of 30 or higher is considered obese. Individuals with very large or small amounts of muscle should note that the BMI formula assumes an average amount of muscle, so that very muscular people may be considered much more overweight and people with very little muscle may be judged less overweight than in actuality.

Beyond a basic diagnosis of obesity, there are further categories to describe varying degrees of severity of obesity. The first category, known as class I obesity, begins at the BMI cutoff point of 30, and includes BMI scores of up to 34.99. Class II encompasses BMI scores of 35 to 39.99. Class III is the highest category formally standardized by the WHO. It includes “morbidly obese” BMI scores of 40 or higher.

In general terms, to be obese is simply to be on the extremely overweight end of the weight spectrum. It does not necessarily warrant being called a disease by itself, but it does often cause several severe illnesses over time. It is important when obtaining a diagnosis of obesity to address the health concerns that are highly correlated with obesity, such as heart disease and diabetes. In addition to these risks, obese individuals are also at a much greater risk for developing illnesses such as sleep apnea, some forms of cancer, and liver disease.



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