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Energy Expenditure Research Using Doubly-Labeled WaterThe doubly-labeled water method is a stable isotope method for measuring Total Energy Expenditure in free living humans. This method is advantageous in that the test subjects are not isolated for indirect calorimetry and are not required to keep accurate records of food intake and body composition. The test subjects can live their daily lives normally.The method is performed by having the test subject submit a pre-dose urine sample for analysis to determine a baseline. The test subject then ingests a bolus dose of 18O and 2H (deuterium) labeled water tracer based on the subject's approximate total body water. Shortly after the dose has been administered and the tracer dose water has reached equilibrium with the body water pool, an additional urine sample is taken for analysis. The subject can then go about their daily lives for two weeks, and then return to the clinic to give a final urine sample. Additional samples at earlier time intervals may be submitted for analysis depending on the activity of the individual. The submitted samples are then analyzed using an Isotope Ratio Mass Spectrometer (IRMS). The IRMS measures the enrichment percentage of the labeled tracer water to the naturally occurring water in all of the submitted samples. The decline in enrichment of the 18O and the 2H is measured to determine the difference in elimination rates. Since 18O is eliminated as both CO2 and H20, and 2H is eliminated only as water, the difference between the elimination rates is a measure of CO2 flux [1]. The CO2 flux can then be used to calculate Total Energy Expenditure. In addition to measuring Total Energy Expenditure, the 2H labeled H20 can be used to very accurately measure Total Body Water. Total Body Water measurements can then be converted to lean body mass and the approximate fat mass can be calculated. Follow the links for more information on how the CNRU Mass Spectrometry Facility can help with your Total Energy Expenditure and Total Body Water assays. 1. Wolfe, Robert R., Chinkes, David L: "Isotope Tracers in Metabolic Research: Principles and Practice of Kinetic Analysis" Second Edition: Wiley and Sons, Inc. 2005. |
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