Doubly labelled water assessment of energy expenditure: principle, practice, and promise

Abstract

The doubly labelled water method for the assessment of energy expenditure was first published in 1955, application in humans started in 1982, and it has become the gold standard for human energy requirement under daily living conditions. The method involves enriching the body water of a subject with heavy hydrogen (2H) and heavy oxygen (18O), and then determining the difference in washout kinetics between both isotopes, being a function of carbon dioxide production. In practice, subjects get a measured amount of doubly labelled water (2H 218 O) to increase background enrichment of body water for 18O of 2000 ppm with at least 180 ppm and background enrichment of body water for 2H of 150 ppm with 120 ppm. Subsequently, the difference between the apparent turnover rates of the hydrogen and oxygen of body water is assessed from blood-, saliva-, or urine samples, collected at the start and end of the observation interval of 1-3 weeks. Samples are analyzed for 18O and 2H with isotope ratio mass spectrometry. The doubly labelled water method is the indicated method to measure energy expenditure in any environment, especially with regard to activity energy expenditure, without interference with the behavior of the subjects. Applications include the assessment of energy requirement from total energy expenditure, validation of dietary assessment methods and validation of physical activity assessment methods with doubly labelled water measured energy expenditure as reference, and studies on body mass regulation with energy expenditure as a determinant of energy balance.

Keywords: Body composition; Body mass regulation; Carbon dioxide production; Doubly labelled water; Energy expenditure; Energy intake; Energy requirement; Motion sensors; Physical activity.

Conflict of interest statement

The author has no conflict of interest.

Figures

Fig. 1

Principle of measurement of carbon dioxide production with doubly labelled water (2H218O). After administration of water labelled with heavy oxygen (18O) and heavy hydrogen (2H), the two isotopes mix with the body water, where 18O exchanges with CO2 in the bicarbonate pools as well. Thus, the elimination rate of 2H (K2) is a measure for water loss (rH2O) and the elimination rate of 18O (K18) is a measure for rH2O plus carbon dioxide production (rCO2), and rCO2 = K18 − K2

Fig. 2

Preparation line for hydrogen gas samples at the Stable Isotope Geology Unit of the Scottish Universities Research and Reactor Centre in East Kilbride, Scotland 1977. The glass system is connected to a rotary pump (1) and a mercury diffusion pump (2) to create high vacuum. A blood-, saliva-, or urine sample in a sealed glass capillary is placed in a tube cracker (3), connected to the system and the system is pumped to vacuum. Then, the capillary is broken and water in the sample is frozen in a U-tube surrounded by liquid nitrogen in a dewar vessel (4). Subsequently, the frozen water is evaporated and passes a uranium furnace kept at 600 °C (5), where it is converted to hydrogen gas. The hydrogen gas is absorbed in a charcoal tube surrounded by liquid nitrogen in a dewar vessel (6). Finally, the charcoal tube with the sample is closed and transferred to an isotope ratio mass spectrometer for analysis

Fig. 3

Frequency distribution of the value of the physical activity level, total energy expenditure as a multiple of resting energy expenditure, including all adult subjects with doubly labelled water-assessed energy expenditure in Maastricht until 2016: women (N = 358, closed bars) and men (N = 490, open bars)