Define measuring body composition- Multiple isotope Dilution?

Multiple isotope dilution (Total and extracellular body water): It is based on the principle that certain substances distribute themselves evenly within the specified fluid compartments. After time has been allowed for this distribution to take place, a blood sample can be analyzed for the concentration of the substance. Deuterium oxide, radioactive tritium oxide and antipyrine distribute evenly throughout all body compartments and are used to determine total body water. Insulin is distributed only in the extracellular fluid compartments and can be used to differentiate between the intracellular and extracellular compartments.