BMI is a method of evaluating obesity that is regarded as accurate by such institutions as the Centers for Disease Control and Prevention, and the World Health Organization. By monitoring BMI, or body mass index, across populations, these institutions can more readily evaluate trends such as the rampant growth of global obesity, an epidemic that the WHO refers to as "globesity."
How is BMI measured?
BMI is a calculation based on your weight and height. The CDC states that in most cases, BMI offers an accurate assessment of the body fat level of an individual, without directly measuring body fat. In order to determine your own BMI, first determine your height in inches and multiply this number by itself. Now take your weight in pounds and divide it by that first number, your height in inches squared. Multiply this number by 703. The final result is your BMI.
How is BMI interpreted?
The interpretation of BMI depends on the subject's age and sex. If you are age 20 or older, a normal BMI is considered to be between 18.5 and 24.9. Anything lower is considered underweight. A BMI between 25 and 29.9 is considered overweight. Anything above 30 is considered obese. For those under the age of 20, your BMI is calculated the same as it is for adults, but interpreting your BMI is approached somewhat differently, by comparing it to a BMI-for-age growth chart. This will tell you where your BMI stand in a percentile range. Those with a BMI under the 5th percentile are considered underweight. A healthy weight lands between the 5th and the 85th percentile. A BMI in the 85th to 95th percentile is considered overweight. Obesity is considered to be the status of those above the 95th percentile.
Alternatives
Other methods exist for evaluating healthy body weight and obesity. These include skin fold measurements, underwater weighing, and bioelectrical impedance. However, according to the CDC these methods are often more expensive and difficult to access than BMI, and can require the use of trained personnel. For these reasons, BMI remains the most common standard used to evaluate obesity.
Debates over BMI
According to the World Health Organization, debate exists over the need for different BMI ranges for different ethnic groups due to difference in associations between body fat distribution, especially among Asian and Pacific populations. The WHO is currently reviewing the relationship between BMI, waist measurements, morbidity and other health risks.
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