Energy expenditure in free-living smokers and nonsmokers: comparison between factorial, intake-balance, and doubly labeled water measures.

Free-living energy expenditure (EE) was measured in 11 smokers (6 females, 5 males) and 10 nonsmokers (6 females, 4 males) by using three methods. Factorial measures (FEE) used measured basal metabolic rate (BMR), records of time spent in six activity categories over 28 d, and average published energy costs of activities. Intake-balance measures (IBEE) used recorded dietary energy intake and changes in energy stores over 28 d. Doubly labeled water measures (DLWEE) used a two-point method over 8-12 d. Level of activity (1.54 +/- 0.07 and 1.55 +/- 0.06 x BMR) and FEE (9573 +/- 1501 and 9540 +/- 1663 kJ/d) were not different between smokers and nonsmokers, respectively. DLWEE was higher than FEE in both smokers (25.9 +/- 13.5%, P < 0.001) and nonsmokers (10.4 +/- 13.8%, P < 0.05), suggesting factorial underestimation in both groups, although the difference between DLWEE and FEE was significantly greater in smokers than in nonsmokers (P < 0.02). IBEE was higher than FEE in smokers (7.5 +/- 10.1%, P < 0.05) but not different from FEE in nonsmokers (2.7 +/- 16.6%), suggesting factorial underestimation in smokers only. DLWEE was higher than IBEE in smokers (13.8 +/- 12.6%, P < 0.01) but not significantly different from IBEE in nonsmokers (6.2 +/- 16.0%). The discrepancies between DLWEE and IBEE in smokers and DLWEE and FEE in nonsmokers preclude conclusion about absolute levels of daily EE. However, both DLWEE-FEE and IBEE-FEE comparisons suggest that our factorial method underestimates free-living EE in smokers relative to nonsmokers, although the effect is larger with the DLWEE-FEE than with the IBEE-FEE comparison.