<P> Bioelectrical impedance analysis (BIA) is a commonly used method for estimating body composition, and in particular body fat . Since the advent of the first commercially available devices in the mid-1980s the method has become popular owing to its ease of use, portability of the equipment . It is familiar in the consumer market as a simple instrument for estimating body fat . BIA actually determines the electrical impedance, or opposition to the flow of an electric current through body tissues which can then be used to estimate total body water (TBW), which can be used to estimate fat - free body mass and, by difference with body weight, body fat . </P> <P> Many of the early research studies showed that BIA was quite variable and it was not regarded by many as providing an accurate measure of body composition . In recent years technological improvements have made BIA a more reliable and therefore more acceptable way of measuring body composition . Nevertheless, it is not a "gold standard" or reference method . </P>

What is the definition of bia and how is this calculation used