Are “Body Fat Analysis” features on weight scales accurate?

Body-fat-analysis (BFA) features on scales, although widely advertised, are actually problematic in terms of accuracy.  For clarity, it would be best to review the definition of body-fat-analysis:  BFA is the measure of body fat expressed as a percentage of body weight.

The bioelectric method is a very simplistic  method of determining BFA, very inexpensive to produce in a weight scale, and therefore has become a widely featured function in consumer weight scales and some medical scales as well.  A very small electrical current is circulated from the scale up one leg, across the abdominal area, down the remaining leg and back to the scale, where it is measured.  The amount of resistance in the body encountered by the current is quantified by a formula, and a BFA reading is indicated by the scale.

The simplicity of the method, as one would expect,  is its downfall.  Here are a few things that cause the accuracy of the “electric current” method to be questionable:

–  Prior to weighing, any intake or elimination of fluids will cause the impedance (electrical resistance) of the body to vary, skewing the outcome of the bioelectric measurement.  This problem even extends to exercise before weighing, especially in the case of weight resistance training (lifting exercise weights), as the increased taughtness/tone present for the period of time in muscle tissue is also a factor that can effect the reading.

–  Males and females have different amounts of body fat associated with the midsection area of the torso, and the formula applied to the impedance measurement does not differentiate between male and female.

–  Food intake, similar to the effect of hydration, can also effect readings.

The optimal way to use the bioelectric impedance method is to always maintain the exact same conditions, even skin temperature, prior to each measurement.  But in practice, especially in the relaxed environment at home and away from the controlled environment of a medical laboratory, these various factors mitigate against obtaining accurate readings.  In another entry, we’ll discuss alternative methods,  also used in medical scales,  that do not involve the use of the bioelectric method.

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