A method for analysing bioimpedance data for a body segment of a subject, said body segment having an external skin surface, said method comprising: (a) applying alternating current at a plurality of frequencies to at least two points on the external skin surface so as to cause current to pass through the segment; (b) for each frequency, recording the voltage difference between at least two other points on the external skin surface, said recorded voltage differences comprising both magnitude and phase information; and (c) using the recorded voltage differences at the plurality of frequencies to determine at least one numerical value indicative of the muscle, fat, and/or extracellular fluid content of the segment, said numerical values being determined using an impedance model for the segment which comprises at least three parallel paths, one of which consists of a capacitor C M and a resistor R I in series which represent primarily the muscle component of the segment, one of which consists of a capacitor C F and a resistor R F in series which represent primarily the fat component of the segment, and one of which consists of a resistor; wherein the applied alternating currents of step (a) and the recorded voltage differences of step (b) are used to calculate impedance values at the plurality of frequencies and step (c) comprises curve fitting to those impedance values; wherein the curve fitting employs an equation of the type: Z Total = P 1 jπ 3 + P 2 jπ 2 + P 3 jπ + P 4 jπ 3 + Q 1 jπ 2 + Q 2 jπ + Q 3 where (i) Z Total is impedance, ω is angular frequency in radians per second j = √-1, and P 1, P 2, P 3, P 4, Q 1, Q 2 and Q 3 are group parameters which are a function of the electrical components employed in the impedance model; and (ii) the P 1, P 2, P 3, P 4, Q 1, Q 2 and Q 3 values obtained for the subject from the curve fitting are used to determine an R I value and/or an R F value for the subject. (a) applying alternating current at a plurality of frequencies to at least two points on the external skin surface so as to cause current to pass through the segment; (b) for each frequency, recording the voltage difference between at least two other points on the external skin surface, said recorded voltage differences comprising both magnitude and phase information; and (c) using the recorded voltage differences at the plurality of frequencies to determine at least one numerical value indicative of the muscle, fat, and/or extracellular fluid content of the segment, said numerical values being determined using an impedance model for the segment which comprises at least three parallel paths, one of which consists of a capacitor C M and a resistor R I in series which represent primarily the muscle component of the segment, one of which consists of a capacitor C F and a resistor R F in series which represent primarily the fat component of the segment, and one of which consists of a resistor; (i) Z Total is impedance, ω is angular frequency in radians per second j = √-1, and P 1, P 2, P 3, P 4, Q 1, Q 2 and Q 3 are group parameters which are a function of the electrical components employed in the impedance model; and (ii) the P 1, P 2, P 3, P 4, Q 1, Q 2 and Q 3 values obtained for the subject from the curve fitting are used to determine an R I value and/or an R F value for the subject.