Bioelectrical impedance analysis (BIA) is a commonly used method for estimating body composition. 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 and its relatively low cost compared to some of the other methods of body composition analysis. 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, of body tissues, which can be used to calculate an estimate of total body water (TBW). TBW can be used to estimate fat-free body mass and, by difference with body weight, body fat.
Many of the early research studies showed that BIA was quite variable and it was not regarded by many as a 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. Like all assessment tools, the result that you get is only as good as the test you do. Although the instruments are straightforward to use careful attention to the method of use described by the manufacturer should be given. Simple devices to estimate body fat, often using BIA, are available to consumers as body fat meters. These instruments are generally regarded as being less accurate than those used clinically or in nutritional and medical practice.
In 2005 Samsung applied for a U.S. patent for a “Method and apparatus for measuring body fat by using bioelectrical impedance” claimed to have lower error and better repeatability than other devices; the patent application contains much useful detail on bioelectrical impedance measurement .
A number of body fat meters for home use are available, often combined with bathroom scales, which measure body impedance and hence body fat and body water.