The disease of obesity is characterized by an excessive accumulation of body fat. A variety of instruments are available for assessing the amount of fat versus lean tissue in the body. However, due to the expense of these instruments and the time required for body fat assessments, obesity is clinically defined by measures that ‘estimate’ adiposity from body weight, body build, and height.
Body Mass Index (BMI)
The body mass index (BMI) is another measure used to define overweight and obesity and is considered a more accurate estimate of body fatness than IBW. Large population studies find that the BMI generally reflects the amount of excess body fat an adult has, although there are certain exceptions, such as the BMI of a woman who is pregnant, an athlete, a bodybuilder, or the elderly.
Category BMI Range
Normal 18.9 to 24.9
Overweight 25 to 29.9
Class I, Obesity 30 to 34.9
Class II, Serious Obesity 35 to 39.9
Class III, Severe Obesity 40 and greater