Tuesday, November 3, 2009

Body Fat Testing Methods

There are several types of methods used to assess body composition. What exactly does body composition stand for and why is it so important to determine? First of all, body composition is the ratio of lean body mass compared to fat body mass. When you see the percentage number from a test, that number is approximately how much of your body is comprised of fat. These numbers need to be treated just like anything else in life. The extremes are unhealthy. Sometimes people believe they need to get as low as possible. However, there are dangerous levels at the lower boundaries. The human body needs 10-12% essential fat in women and 2-4% in men. This is the fat necessary to protect the organs and maintain a healthy daily living. The numbers on the high side are associated with all kinds of ailments including: hypertension, high cholesterol, and diabetes. The high risk boundaries are >32% for women and > 26% for men. So now that we know the boundaries that we should stay between, how exactly does one measure body fat percentages? Some methods are more accurate than others, but they might not be as realistic to perform. Here are some thoughts on the methods and their relevance.
DEXA (dual energy X-ray absorptiometry) is used to measure bone density. It also is used to measure body fat percentage in addition to where the fat is located. This is a whole body scanner with two different low-dose x-rays to read bone mass and soft tissue mass. The test takes about 10-20 minutes to complete and is highly accurate (2-3% margin of error). This test is painless and is rated as one of the most accurate tests. It usually costs around $100. Insurance may cover this test.
Hydrostatic weighing is another extremely accurate test (2-3% margin of error). For this test, picture being lowered into a big fish tank. One sits on a scale inside a tank of water, then one expels as much air as possible. Next you are lowered underwater and asked to expel even more air, if possible. The accuracy of the test depends on if one is able to blow out all of the air. The simple explanation of how this works is: fat is lighter then water and the more fat you have the more you will float. So the scale measures underwater weight to figure out body density. This test can be a little scary and is certainly not a good option for high risk individuals as it probably will cause a pretty big spike in anxiety levels. The cost for this test is between $25-$50.
Plethysmography is a technique that requires an individual to enter a dual-chamber device. The device measures the air displaced inside the chamber. This is an expensive technique and it has not been thoroughly researched as of yet. The standard error is about 2.2-3.7%.
Calipers are a common sight at most health clubs. This is the device used to measure skin fold thickness at several locations on the body. The basic premise of this test is that the thickness of fat under the skin reflects total body fat. There are several potential flaws with this test. First, a skilled tester is required. One needs to use the same tester for each test to avoid slight variations in testing methods. This test is not that accurate for people that are fat on the inside. Some skinny individuals as well as older adults can fall into this category. The benefits of this test are that it is generally painless and easy to administer.
Bioelectrical impedance is probably one of the fastest and easiest methods to test body fat. A handheld or standing scale is used for this test. An electrical signal passes from hand to hand or foot to foot. The speed of the signal indicates the amount of muscle one carries. The faster the signal the more muscle the individual has. The basic premise of this test is that water conducts electricity. Fat contains almost no water, while muscle is comprised of 70% water. The margin of error of this test is about 4%. The variables that can affect the accuracy of the test are: hydration, food intake, and skin temperature. If one is dehydrated, then the body fat will register at a higher level. The general rule of thumb is test at the same time each day, preferably first thing in the morning after a cup of water.

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