Body Fat Testing

How It Is Done

There are several ways to estimate body fat. The easiest and most popular ways to test are not as accurate as more expensive methods.

The least expensive and most popular tests include:

• Skinfold thickness. A tool called a caliper is used to measure the thickness of fat at one or more places on your body. It is most accurate when a well-trained person measures fat thickness from several sites.
• Bioelectrical impedance. A small electrical current is passed through your body to measure your body's electrical resistance. This resistance is used along with your height and weight to calculate your body fat. Results can vary based on how much water is in your body and where the electrodes are placed. You can buy some devices, including body fat scales, that calculate your percentage of body fat using this method.

More accurate tests are available, but they can be harder to find and can cost a lot. They include:

• Underwater weighing. This is also called hydrodensitometry. It is based on the principle that fat tissue is less dense than muscle and bone.
• DXA. This is also called dual-energy X-ray absorptiometry. DXA is a type of X-ray that can tell how much fat tissue you have and where it is.
• Air displacement plethysmography. This is similar to underwater weighing, but it uses air instead of water.

Results

The results of a body fat test give an estimate of how much of your body weight comes from fat.

But body fat percentage is not the best way to measure your risk for weight-related diseases. Your doctor may suggest checking your BMI (body mass index) and your waist size instead. A higher BMI or waist size may mean that your weight is raising your risk for health problems.