Is Bioelectrical Impedance Accurate?
The general principle behind Bioelectrical Impedance (BIA): two conductors are held (on the hand held unit) and a small electrical current is sent through the upper body from one to the other.
The resistance between the conductors will provide a measure of body fat, since the resistance to electricity varies between adipose, muscular and skeletal tissue. Fat-free mass is more than 70% water and a good conductor of electrical current, while fat is a poor conductor. Based on the rate that electricity is conducted, a formula is used to estimate percentage of fat and lean body mass.
One problem with the formulas is they don’t seem to predict accurately for different ethnic groups. Another drawback to using the hand-held unit is they only measure upper body impedance; units that use hand and foot sensors give a better estimation since they measure impedance across the entire length of the body. Results from hand-held units may also vary due to individual differences in arm span/height ratios. Finally, results may be skewed by dehydration.
This study found the handheld units measured results that were reproducible but either over estimated or under estimated % fat mass in overweight women.
Despite these drawbacks, I still like the hand-held unit. It’s quick, easy, and gives you a result that in my opinion is in the ballpark for 70-80% of those I test. Since the results are highly reproducible, it also offers a very good measure of fat loss in subjects that do lose total body weight.
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