How does Bioelectric Impedance Analysis work?

It generally measures the impedance of current through the body. It measures the opposition of the tissues in the body against the current discharges. This allows the calculation of various current frequency and their relative measurements, and are able to estimate the total body water weight. This data along with the individuals age, weight, sex and such and used in pre-derived equations to calculate fat % and such. The test's accuracy on the other hand may be questioned.