As our knowledge of obesity has grown, the way physicians
define obesity has changed.
The original definition of morbid obesity
was any individual who was greater than or equal to twice their
ideal body weight, or greater than or equal to 100 pounds above
their ideal body weight. The figures for ideal body weight were
determined by the 1983 Height and Weight Standards of the
Metropolitan Life Insurance Company.
Morbid obesity was also defined by the amount of total body
fat, although this value is not easily obtained. Normally 20 to
25 percent of body weight is fat. If 40 percent or more of the
body weight is fat, morbid obesity is diagnosed.
The modern definition of obesity is based
on body mass index (BMI), a calculation that
compares your weight (measured in kilograms) with your height
(measured in meters, then squared). It was developed through a
collaboration between the National Institutes of Health’s
National Heart, Lung, and Blood Institute and the North
American Association for the Study of Obesity.
Using this calculation (BMI=kg/m2), which can be done online,
you can determine how physicians would classify your body’s
current size.
- BMI of less than 24.9 is considered normal.
- BMI between 25 and 29.9 is considered overweight.
- BMI of 30 or greater is considered obese.
Obese patients are placed in three classes, based on their
BMI:
- Class 1 = 30 to 34.9
- Class 2 = 35 to 39.9
- Class 3 = 40 to 49.9
Class 3 BMI is required to be diagnosed morbidly obese.
Individuals with a BMI that is greater than 49.9 are considered
super obese.
Waist circumference is also an important
consideration in determination of the health risks related to
obesity. Men with a waist circumference greater than 40 inches
and women with a waist circumference greater than 35 inches are
at increased risk of complications.
To reflect this increased risk, the classifications defined
by BMI can be increased one level.
Back to: Understanding Obesity overview
Next: Causes of Obesity
