Differences in Energy Expenditure between Respiratory Chamber and Metabolic Ward in Inpatient Men and Women

We previously investigated 16 men with overweight or class I obesity who were admitted to a metabolic ward and engaged in 90 minutes of daily cycle ergometry at a fixed resistance. Subjects resided in a respiratory chamber for 2 days per week. The remaining days were spent in their inpatient rooms. Total expenditure was measured over 2 weeks via doubly labeled water (DLW). We found a surprisingly large (∼500 kcal/day) decrease in expenditure when subjects resided in the respiratory chamber as compared to the days spent in their rooms. Here, we attempted to reproduce this finding in non-exercising healthy volunteers.

Purpose: To measure differences in daily energy expenditure between days spent on a metabolic ward vs. days spent in a respiratory chamber.

Methods: 10 adults (2 M, 8 F) aged (mean ± SE) 34 ± 3.5 years with BMI 27.9 ± 2.3 kg/m² completed a 7-day inpatient stay on the metabolic ward at the NIH Clinical Center. Two days were spent residing in a respiratory chamber. Study participants received a controlled diet and refrained from exercise. Temperature and clothing were kept constant. Energy expenditure on days spent on the ward was calculated using DLW over 6 days after accounting for the energy expended during the 2 respiratory chamber days.

Results: Average energy expenditure on the ward was 2122 ± 155 kcal/day, with an average of 1996±130 kcal/day expended during the two respiratory chamber days. Therefore, energy expenditure on the metabolic ward was 126 ± 55 kcal/day (p= 0.048) greater than in the respiratory chamber.

Conclusion: Participants expended ∼126 kcal/day more on the metabolic ward than in the respiratory chamber. This was a much smaller discrepancy than previously found in exercising men. Failure to reproduce our previous results may have been due to the lack of exercise, the inclusion of women, or the wider range of BMIs in the current study. Further studies are needed to investigate the determinants of energy expenditure differences between ward and respiratory chamber days.