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
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
Reviewed by the Department of Nutrition Therapy at The
Charlotte Grayson, MD, WebMD, August 2004.
Portions of this page ©
The Cleveland Clinic 2000-2004