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 th e doubly-labelled water (DLW) technique. To examine the limitation of the D LW measurement of energy expenditure for evaluating reported energy intake. To estimate the probable minimum and maximum 'habitual' energy expenditure s far 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% far 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 lime points CVw for PAL was 9.1%, 10.0% and 13.4% res pectively. Pooled mean CVt was 13.0% for EE and 10.7% for PAL. CVb calculat ed from pooled mean CVt and CVw was 20.6% for EE and 7.2% for PAL. 95% conf idence limits of PAL in 11 age-sex groups averaged 1.2 to 2.2. Conclusions: The analysis supported previous estimates of 8% for within-sub ject variation in DLW measurements including analytic plus inherent biologi c 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 e nergy 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.