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How to Measure Body Fat

When it comes to weight loss, the ordinary weighing scale does not tell the whole truth. Your body weight does not reflect how much is fat and how much is muscle or lean body tissue.

To find out how much fat you have, you need to use a body fat measurement technique. The two most practical methods for the average person are skinfold measurements and bioelectrical impedance. Here are their pros and cons, and tips to make each method more accurate.

All Methods Have an Error Rate.
Many body fat measurement methods claim to be the most accurate, but the most accurate one is an autopsy. Obviously, this is one method not even the most fat-obsessed person is willing to undergo.

From dissections, scientists have been able to make assumptions about how much fat is stored under the skin (about 50 percent) or stored around internal organs and how much of the body is water (approximately 50 to 70 percent). From these assumptions, scientists have derived what is called ‘’prediction equations’’.

All the measurement methods rely on these equations. Unfortunately, the equations themselves can be a source of error because most of the equations were developed using White or Caucasian populations.

Vivian Heyward, exercise scientist at the University of New Mexico, has done a comprehensive analysis based on 75 studies on which method is best for which ethnic group. According to her, no one method can claim to be the ‘’gold standard’’ for all races.

All the methods have a 3 to 4 percent error factor because of the ‘’prediction equations’’. This means that if your body fat was measured at 20%, you could be as low as 17 percent or as high as 23 percent. This error rate gets even worse if the person taking your measurement does not do it properly.

Bioelectrical Impedance
This method is based on the assumption that water is a good conductor of electricity. A muscle cell is 75 percent water and a fat cell is only 5 to 13 percent water. In traditional BIA or bioelectrical impedance, a harmless electrical current is passed through electrodes that are placed on the hand and foot while the person lies down. A machine measures how fast or slow the electrical current travels. The slower the current, the more fat the person has because fat ‘’impedes’’ the flow of electricity.

BIA is convenient because the test only takes ten minutes. The person being tested doesn’t have to undress and there is minimal physical contact with the tester. The test can be used with children over eight years of age and with pregnant women.

BIA is appropriate for all races and genders (except for Blacks), though it tends to overestimate body fat in very lean people and underestimate body fat in very obese people.

Certain guidelines have to be followed to ensure that the error rate doesn’t go beyond 4 percent. No eating or drinking within four hours of the test. No exercise within 12 hours of the test. Urinate within 30 minutes of the test. No alcohol consumption within 48 hours of the test. No diuretics within seven days of the test.

Home fat monitor scales use a “leg to leg” connection. All you have to do is stand on the scale in your bare feet, and the built-in electrodes take your body fat measurement. To get accurate results, follow the protocol guidelines above. Otherwise, you will get results with a much wider range of error.

Skinfold Measurements
This is also known as the “pinch an inch” test. It involves measuring the fat under the skin with a special caliper.

Much of the success of this method depends on the skill of the person giving the test and the kind of caliper that is used. Plastic calipers should only be used by highly skilled technicians.

It is relatively easy to train people to do the test, but they must practice on at least 100 people before they can master the technique because many things can go wrong. The tester may not pinch the same exact spot each time, may not pinch all the fat away from the muscle, or may pinch part of the muscle together with the fat.

Since “pinching” techniques can vary widely, use the same tester with the same type of caliper each time you take a re-test. Get tested before you exercise since blood travels to the surface of the skin when you exercise. Your skinfold measurement will be artificially bigger than it should be. Do not use oils or lotions because the tester’s fingers will be sliding all over the place.

Some other disadvantages are that you have to undress and the tester has to touch your body at several places. The test is not appropriate for very obese individuals since the jaws of the calipers cannot open wide enough. The skinfold method is appropriate for all races except for male Native American Indians.

The biggest disadvantage is that the equations are based on the assumption that everyone stores 50 percent of their total storage fat under their skin. This is not true for everyone, especially as people get older.

The Best Way to Use Body Fat Measurements.
Don’t get hung up on the actual fat percentage calculated. Use the tests as a way to judge your progress in losing body fat. Use the same kind of test each time. Do not try to compare the results of one kind of test with another. It would be like “comparing apples to pears”.

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