The doubly-labelled water method using stable isotopes of hydrogen and oxygen, is rapidly becoming established as an important new tool for investigating energy metabolism. It is the first genuinely non-invasive method for measuring energy expenditure in free-living people, providing estimates of habitual expenditure over a time period of 10-20 days. The accuracy and precision of these estimates should be superior to those obtained by traditional factorial methods.
The doubly-labelled water method, developed and applied to humans in eight research centres, has already been used in premature babies, neonates, infants, children, pregnant and lactating women, normal and obese adults, athletes, hospitalised patients and in the elderly. In spite of this, several aspects of the method have not been standardised.
This report is the outcome of a workshop convened to standardise the doubly-labelled water method. It was sponsored by the International Dietary Energy Consultancy Group (IDECG), financed by the Nestlé Foundation, organised by Dr Andrew Prentice, and took place in Cambridge, U.K., from September 2629, 1988.
All the eight research centres using the method in humans and two who had done pioneering work in animals were represented at the workshop. Data sets and position papers on various aspects of the method were exchanged among centres prior to the meeting. The main issues discussed at the workshop were isotopic pool sizes and flux rates, estimates of error, fractionation effects, isotope exchange, effects of changes in isotopic background, the energy equivalent of CO2, problems of mass spectrometry and problems arising when the method is used in special groups of humans like premature babies and certain categories of hospitalised patients. The discussion was very open and consensus could be reached on all important issues.
The Section of Nutritional and Health-Related Environmental Studies of the International Atomic Energy Agency (IAEA) supported the publication of this document within the framework of its Co-ordinated Research Programme on Applications of Stable Isotope Tracers in Human Nutrition Research. The methods described here are also expected to be applicable in some future IAEA projects dealing with other, more specific, aspects of energy metabolism in third world populations.
The organizations and scientists involved in this venture hope that this report will serve future users of the doubly-labelled water method by providing them with a sound and agreed upon methodological basis.
Robert M. Parr
IAEA, Vienna
Beat Schürch
Nestle Foundation, Lausanne