Within- and between-subject variation in energy expenditure measured by the doubly-labelled water technique: implications for validating reported dietary energy intake.

OBJECTIVES: To estimate the total (CVt), within-subject (CVw) and between-subject (CVb) variation in free-living energy expenditure as measured by the doubly-labelled water (DLW) technique. To examine the limitation of the DLW measurement of energy expenditure for evaluating reported energy intake. To estimate the probable minimum and maximum 'habitual' energy expenditures for a sustainable lifestyle.
DESIGN: Review and analysis of individual data from 25 studies with repeat DLW measurements of energy expenditure (EE).
RESULTS: Pooled mean CVw derived from 21 studies was 11.8% for EE and 12.3% for physical activity level (PAL). Multiple regression analysis of CVw in 25 studies found a positive association with time span between measurements. At zero time CVw for EE was 8.2% rising to 9.6% at 13 weeks and 15.4% at 52 weeks. At the same time points CVw for PAL was 9.1%, 10.0% and 13.4% respectively. Pooled mean CVt was 13.0% for EE and 10.7% for PAL. CVb calculated from pooled mean CVt and CVw was 20.6% for EE and 7.2% for PAL. 95% confidence limits of PAL in 11 age-sex groups averaged 1.2 to 2.2.
CONCLUSIONS: The analysis supported previous estimates of 8% for within-subject variation in DLW measurements including analytic plus inherent biologic variation. Variation that included changes in weight, season and activity increased with increased time between measurements to about 15% at a time span of 12 months. Confidence limits of agreement between EE and reported energy intake were estimated to range from +/-15% to +/-32%. Estimates of the range of usual EE for normally active persons ranged from 1.3 to 2.2.