Energy expenditure during heavy work and its interaction with body weight

The present study was designed to investigate the interaction between body weight and energy expenditure in well-nourished individuals. Energy expenditure was determined during a 10 d highly controlled work programme in apparently well-nourished adult male construction workers with a wide range of body weights (mean weight: 63.9 (SD 11.0, range 46-7-80.1) kg, mean BMk 22.5 (SD 3.8, range 16.7-28.9) kg/m2). Total energy expenditure (mean: 12.68 (SE 0.73) MJ/d or 1.78 (SE 047) x BMR) was determined using doubly-labelled water and the energy costs of work activities by Oxylog. The energy expenditure during work (mean: 5.75 (SE 0.29) MJ/day or 3.48 (SE 0.09) x BMR) was estimated from the energy costs of individual tasks and the time spent in those tasks. The energy expenditure during discretionary time (mean: 4.37 (SE 0.58) MJ/d or 1.49 (SE 0.17) x BMR) was calculated by subtracting occupation and sleep expenditure (taken as 1 x BMR) from total expenditure. Food intake and discretionary time allocation were recorded by the subjects. The energy expenditure in the programmed work activities (expressed as a multiple of BMR) showed a simcant increase (P = 0.035) with increasing body weight, suggesting that the assumed constancy of BMR multiples across a wide range of body weights may not be valid. This assertion was supported by theoretical calculations based on empirically derived equations. In order to avoid errors which could be interpreted as metabolic ‘adaptation’ it may be necessary to take account of body weight when using the BMR-multiple approach to estimate energy requirements at low body weights.