W A Coward, MRC Human Nutrition Research, Cambridge, UK
© 2005 Elsevier Ltd. All rights reserved.
Like methods for the measurement of energy expenditure by respiratory gas analysis, the doubly labeled water (DLW) method is indirect. The disappearance of stable isotope tracers, given orally, is used to model water and water plus carbon dioxide turnover. Carbon dioxide production rate is then estimated by difference and energy expenditure calculated from it. In practice, this means that subjects merely drink labeled water, samples of body water (e.g., urine, saliva, or blood) are collected over a few days, and these are then passed to the laboratory for tracer analysis and calculation. The method is thus uniquely objective; it is noninvasive and non-restrictive in that its application does not interfere with normal lifestyles and comparable results can in principle be obtained in any circumstances without subject or observer influence. Complex measurement techniques do not need to be exported to the site where the subjects are located. However, underlying the apparent simplicity are concepts and techniques that are not commonly tools of trade for many potential users of the methodology. In a complete review, these, as well as method practice and results, need to be explained.
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