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Total Body Water Assay for Obsity ResearchThe CNRU Mass Spectrometry Core Facility offers assistance in methods development and mass spectrometry analysis to help researchers determine total body water using doubly-labeled water stable isotope methods.Total body water (body composition) has been measured using stable isotopes of oxygen (18-Oxygen) and deuterium (deuterium oxide, D2O) for more than 40 years. It is a very useful technique to estimate lean body mass since it is completely safe, requires only periodic sampling of body fluids, and is non-restrictive. The principle is based on the theory that water is distributed in all parts of the body except body fat. In a typical total body water study, subjects fast for at least 2 hours and a "pre" baseline plasma, salive or urine sample is collected. Heavy water is precisely weighed and a dose is administered either orally or intravenously. A second sample is collected after complete equilibrium has been reached, which usually takes 3-6 hours. The resulting HD gas is measured against a lab reference gas (hydrogen gas generated from tap water) using an isotope ratio mass spectrometer. Total body water is calculated from the pre and post deuterium dose dilutions. Total body water values are then converted to kilogram amounts and lean and fat body mass can be determined. The methodology is described by Scrimgeour, C.M., Rollo, M.M., Mudambo, M.K.T., Handley, L.L. and Prosser, S.J. (1993) 'A simplified method for deuterium/hydrogen isotope ratio measurements on water samples of biological origin' Biological Mass Spectrometry, 22: 383-387. Click for more detailed information on the calculations and models used in total body water studies. |
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