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Bioelectrical Impedance Analysis

Your total body water constitutes the largest component (72%) of your fat-free body weight. Bioelectrical impedance analysis (BIA) is based on the fact that the body contains intracellular and extracellular fluids capable of electrical conduction. A non-detectable, safe, low-level current flows through these intracellular and extracellular fluids. Since your fat-free body weight contains much of your body's water and electrolytes, it is a better conductor of the electrical current than the fat, which contains very little water. So this technique is essentially an index of total body water, from which fat-free mass is estimated.

The popularity of the BIA method has grown significantly over the last few years because it is painless, quick, and easy to administer the test. To take the test, you lie on a testing table or floor and electrodes are attached to your hands and feet. You do not feel a thing as the current passes through your body. Average time for administering this test is about 10 minutes. The following BIA testing guidelines are important in order to keep the prediction error of the BIA method at no more than 4% (Heyward, 1991).
1. No eating or drinking within 4 hours of the test
2. No exercise within 12 hours of the test
3. Urinate within 30 minutes of the test
4. No alcohol consumption within 48 hours of the test
5. No diuretics within 7 days of the test
One drawback of using the BIA method is that the equipment is relatively expensive ($3,500 compared to skinfold calipers at $200). Also, it appears that the BIA method is more accurate for estimating body fat of persons within the optimal health category (18-30% women; 10-25% men). There is a tendency for BIA to overestimate percent body fat in very lean clients and underestimate body fat in obese clients. All in all, if the guidelines for testing are followed, the BIA method is a satisfactory method for assessing body composition of most people.

Tongfang Health Technology (Beijing) Co.,Ltd