Measuring the impedance of a human body region at a high frequency (ZHF) and a low frequency (ZLF). ZHF is used to obtain the value of the volume of fluid in the tissues of the region. ZLF is used to obtain the value of the volume of extracellular fluid in the tissues. The increase in the metabolic component in the volume of extracellular fluid is determined by the increase of the volume of all of the fluid in comparison with the previous measurement, determining the increase in the volume of extracellular fluid in comparison with the previous measurement and subsequently calculating the difference between the increases in the volume of all of the fluid and the volume of extracellular fluid. The glucose concentration G(tk) is determined by adding the amount of increase in the glucose concentration and the value of the glucose concentration determined at the previous measuring stage.