Energy expenditure and substrate metabolism measured by 24 h whole-body calorimetry in patients receiving cyclic and continuous total parenteral nutrition
1. Twenty-four hour energy expenditure and its components, i.e. 'basal metabolic rate', activity energy expenditure and diet-induced thermogenesis were measured, using continuous whole-body indirect calorimetry, in patients receiving total parenteral nutrition while in remission from Crohn's disease (weight 51.9 +/- 9.9 kg, body mass index 19.2 +/- 2.0 kg/m2). 2. Total parenteral nutrition was infused continuously over 24 h in four subjects and cyclically, between 22.00 and 10.00 hours, in eight subjects. Twenty-four hour energy expenditure (6.83 +/- 1.10 MJ/24 h) was lower than total energy intake (10.09 +/- 1.63 MJ/24 h), resulting in a positive energy balance (3.26 +/- 1.42 MJ) in all subjects. Repeated measurements of resting energy expenditure in the continuously fed subjects (5.82 +/- 1.11 MJ/24 h) did not change significantly at different times of day (coefficient of variation 2.2-6.6%). In contrast, in cyclically fed subjects, resting energy expenditure was 24.2 +/- 9.0% higher towards the end of the 12 h feeding period than the 'basal metabolic rate', which was measured just before the start of the feeding period. 3. Diet-induced thermogenesis, calculated as the increment in resting energy expenditure above 'basal metabolic rate' over the 24 h period (adjusted for the reduction in energy expenditure during sleep), was found to be 0.60 +/- 0.29 MJ or 6.1 +/- 3.1% of the energy intake. 4. The energy cost of activity (activity energy expenditure) in the continuously fed patients, calculated as the difference between 24 h energy expenditure and the integrated 24 h measurements of resting energy expenditure, was 0.88 +/- 0.53 MJ, i.e. 12.9 +/- 5.9% of the 24 h energy expenditure. 5. The non-protein non-glycerol respiratory quotient exceeded 1.0 for varying periods of time (0.5-17 h) in 11 subjects, indicating net lipogenesis from carbohydrate. 6. The results demonstrate favourable rates of deposition, during intravenous feeding, of both energy and nitrogen over a 24 h period in patients recovering from an episode of Crohn's disease. The efficacy of these commonly used total parenteral nutrition regimens in these patients is related to three features that are absent in normal healthy individuals, namely a low basal metabolic rate, a low activity-related energy expenditure and prolonged periods of lipogenesis from carbohydrate.