Doctors usually define "overweight" as a condition in which a person's weight is 10%-20% higher than "normal," as defined by a standard height/weight chart.
Obesity is usually defined as a condition in which a person's weight is 20% or more above normal weight. "Morbid obesity" means a person is either 50%-100% over normal weight, more than 100 pounds over normal weight, or sufficiently overweight to severely interfere with health or normal functioning.
Nearly 40 million Americans, more than one-quarter of all adults and about one in five children, are obese . Each year, obesity causes at least 300,000 excess deaths in the U.S. and costs the country more than $100 billion.
There are several tests that can be performed to determine if you are overweight or obese. But, measuring the exact amount of a person's body fat is not an easy task. Some tests are more accurate than others.
What Tests Are Available for Diagnosing Obesity?
- Hydrostatic body fat test. This is the most accurate test given to assess body fat. During the test, you are submerged in water while your underwater weight is recorded.
- Dual energy X-ray absorptiometry (DEXA). This is another very accurate way to assess body fat. During this test, the patient must lay supine for approximately 20-30 minutes while every section of their body is systematically X-rayed.
Unfortunately, these methods, however accurate, are not practical for the average person, and are done only in research centers with special equipment. As a result, doctors have developed easier methods to determine if a person is overweight or obese. These include:
- Calipers. A caliper is a device that is used to measure the amount of body fat on different parts of the body. Special computations provide your percentage of body fat based on the various measurements of skinfold thickness. These devices are commonly used in health clubs and commercial weight loss centers, but the results are only accurate if performed correctly.
- Bioelectrical impedence, or BIA. This technique uses a machine that sends harmless and painless electricity through a person's body to "weigh" each of the different kinds of tissue in their body. These include the amount of muscle and other lean tissue as well as the amount of fat and water in their body. The greater amount of fat a person has the greater the resistance the electrical signal encounters. BIA is very accurate and is often available to the public for purchase or can be found at gyms and rehabilitation centers.
- Height/weight charts. Special tables can be used to determine if a person is overweight. To get your ideal weight, you find you height on the chart, decide if your thick or thin framed and then you can find the range of your ideal weights separate for males and females. However, this technique is not always accurate. For example, the height/weight tables could indicate that a lean, muscular person is "overweight" (muscle weighs more than fat) while a person whose weight is within the "normal" range might actually be carrying around more fatty tissue than is healthy.
- Body mass index. The BMI is now the most common tool used to measure obesity. It measures your weight relative to your height. The ideal range is 18.5-24.9. A person with a BMI between 25 and 30 is considered to be overweight and a BMI over 30 indicates obesity.