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OBESITY, DIABETES, AND ARTHRITIS
How is Obesity Defined and Categorized?
Obesity is defined as excess adipose tissue. The most common measure used is Body
Mass Index (BMI), which is calculated by dividing a person’s weight in kilograms by height
in meters squared. The mathematical formula is “weight (kg)/height (m²).” Charts and online
BMI calculators are readily available. BMI is the measurement of choice for many obesity
researchers and other health professionals, as well as the definition used in most published
information on overweight and obesity.
An expert panel convened by the National Heart, Lung, and Blood Institute (NHLBI) in
cooperation with the National Institute of Diabetes and Digestive and Kidney Diseases
(NIDDK), both part of NIH, identified overweight as a BMI of 25 to 29.9 kg/m², and obesity as
a BMI of 30 kg/m² or greater in its 1998
Clinical Guidelines on the Identification, Evaluation,
and Treatment of Overweight and Obesity in Adults
.
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As noted in Table 1, the
Guidelines
identify three levels of obesity. Defining overweight as a BMI of 25 or greater is consistent
with the recommendations of the World Health Organization and most other countries. These
definitions, widely used by the Federal Government and more frequently by the broader
medical and scientific communities, are based on evidence that health risks increase in
individuals with a BMI > 25.
Table 1 – BMI Categories
BMI
Category
Below 18.5
Underweight
18.5-24.9
Normal Weight
25.0-29.9
Overweight
30.0-34.9
Grade 1 Obesity (sometimes called moderate obesity)
35.0-39.9
Grade 2 Obesity (sometimes called severe obesity)
40 and greater
Grade 3 Obesity (sometimes called morbid or extreme obesity
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(sometimes called super obesity)
BMI is not gender-specific in adults, and does not directly measure percentage body fat
but it is a more accurate indicator of overweight and obesity than relying on weight alone.
Calculating BMI is simple, quick, and inexpensive, but it does have limitations. One problem
with using BMI as a measurement tool is that very muscular people may fall into the
“overweight” category when they are actually healthy and fit. Another problem with using BMI
is that people who have lost muscle mass, such as the elderly, may be in the “healthy weight”
BMI category (BMI 18.5 to 24.9) when they actually have reduced nutritional reserves. BMI,
therefore, is useful as a screening tool for individuals and as a general guideline to monitor
trends in the population, but by itself is not diagnostic of an individual patient’s health status.
Further assessment of patients should be performed to evaluate their weight status and
associated health risks.