RELIABILITY OF THE DOUBLY LABELED WATER METHOD FOR THE MEASUREMENT OFTOTAL DAILY ENERGY-EXPENDITURE IN FREE-LIVING SUBJECTS

The reliability of the doubly labeled water method for measuring total daily energy expenditure (TDEE) was measured in six adult women at a 6-mo interval. The contribution of random error to reliability was ass essed by repeating each isotopic analysis. Physiologic variation was c alculated from the difference between the total variance and the analy tic variance. In addition, postaborptive resting metabolic rate and th ermic effect of a meal were measured to partition the physiologic vari ation in TDEE into its three components. No seasonal effect (summer-wi nter) in TDEE was detected in these six subjects. The within-subject c oefficient of variation for TDEE was 7.8%, of which physiologic variat ion was 6.4%. Within-subject variation in physical activity was the ma jor source of variation in TDEE. Review of the 16 published studies, i n which at least two measurements of TDEE by doubly labeled water were performed in each subject, indicated that the reliability of the meth od is 7.8%, except under conditions of high water flux. Care, however, must be taken to ensure that the analytic contribution does not infla te this figure in any given laboratory.