The measurement of total energy expenditure is fundamental in nutritional and metabolic studies. Doubly labeled water is a form of indirect calorimetry, which measures precisely and accurately total energy expenditure in free-living individuals. This method has been applied for several ends, such as to measure energy expenditure during chronic illness and physical activity. It has also been used in studies concerning the consequences of malnutrition and the etiology of obesity, demonstrating the inter-racial differences in total energy expenditure in particular. The technique can also be used to validate other methods of physical activity assessment and total energy expenditure estimates. Although many validation studies have been conducted, none demonstrated good individual performance. Finally, the doubly labeled water has been widely applied in developed countries as a marker of energy intake, validating the energy intake estimates derived from dietary assessment methods. This application should also be encouraged in developing countries, in order to establish the error associated with energy intake estimates obtained by the dietary assessment methods used in the human nutrition studies of these nations.
doubly labeled water; physical activity; energy expenditure; obesity; underreporting