Method of measuring of a concentration of blood glucose in a human, the method comprising: using spaced apart electrodes attached to a region of a body of the human to successively measure values of high frequency impedance and low frequency impedance of the region at predetermined time intervals; using a measured value of the high frequency impedance to determine an estimate of a volume of fluid in tissue of the region between the electrodes; using a measured value of the low frequency impedance to determine an estimate of a volume of an extracellular fluid in the tissue in the region between the electrodes; determining an increment of a metabolic component of the volume of the extracellular fluid by: determining an increment of the estimate of the volume of the fluid relative to a previously measured value of the volume of the fluid; determining an increment of the estimate of the volume of the extracellular fluid relative to a previously measured value of the volume of the extracellular fluid; determining a difference between the increment of the estimate of the volume of the fluid and the increment of the estimate of the volume of the extracellular fluid; determining an increment of the concentration of the blood glucose by normalizing the increment of the metabolic component of the volume of the extracellular fluid; and determining the concentration of the blood glucose by adding up the increment of the concentration of the blood glucose and a previously determined concentration of the blood; wherein determining a concentration of the blood glucose at a first time interval comprises adding up an increment of the concentration at the first interval of time and an initial blood glucose concentration. using spaced apart electrodes attached to a region of a body of the human to successively measure values of high frequency impedance and low frequency impedance of the region at predetermined time intervals; using a measured value of the high frequency impedance to determine an estimate of a volume of fluid in tissue of the region between the electrodes; using a measured value of the low frequency impedance to determine an estimate of a volume of an extracellular fluid in the tissue in the region between the electrodes; determining an increment of a metabolic component of the volume of the extracellular fluid by: determining an increment of the estimate of the volume of the fluid relative to a previously measured value of the volume of the fluid; determining an increment of the estimate of the volume of the extracellular fluid relative to a previously measured value of the volume of the extracellular fluid; determining a difference between the increment of the estimate of the volume of the fluid and the increment of the estimate of the volume of the extracellular fluid; determining an increment of the estimate of the volume of the fluid relative to a previously measured value of the volume of the fluid; determining an increment of the estimate of the volume of the extracellular fluid relative to a previously measured value of the volume of the extracellular fluid; determining a difference between the increment of the estimate of the volume of the fluid and the increment of the estimate of the volume of the extracellular fluid; determining an increment of the concentration of the blood glucose by normalizing the increment of the metabolic component of the volume of the extracellular fluid; and determining the concentration of the blood glucose by adding up the increment of the concentration of the blood glucose and a previously determined concentration of the blood; wherein determining a concentration of the blood glucose at a first time interval comprises adding up an increment of the concentration at the first interval of time and an initial blood glucose concentration.