Validity and reproducibility of a whole-room indirect calorimeter for measurement of the thermic effect of food.

Abstract

Whole-room indirect calorimeters (WRICs) measure respiratory exchange, energy expenditure, and macronutrient oxidation. The thermic effect of food (TEF) that occurs after food intake due to digestion, absorption, and storage of nutrients is an important component of daily energy expenditure, but difficult to quantify using metabolic carts. This study evaluated the validity and reproducibility of a 7209 L WRIC for TEF measurement. Technical validation was performed with 7-h propane combustion tests (n = 5), and biological reproducibility was tested in 10 healthy subjects (6 men, mean age 33.5 ± 10.3 years) in replicate 7-h measurements, after a 3-day run-in protocol. Coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated for ventilation rates of O 2 (VO 2 ) and CO 2 (VCO 2 ), respiratory exchange ratio (RER; VCO 2 /VO 2 ), postprandial energy expenditure, and TEF. Technical validation showed good validity with CVs ranging from 0.23% for RER to 1.74% for energy expenditure. For biological reproducibility, CVs were 3.42%, 1.97%, 2.58%, 3.07%, and 27.48% for VO 2 , VCO 2 , postprandial RER, postprandial energy expenditure, and TEF, respectively. ICCs were excellent for VO 2 (96%), VCO 2 (98%), and postprandial energy expenditure (96%), but poor for TEF (24%). In conclusion, the 7209 L WRIC is technically valid and reproducible for ventilation rates and postprandial energy expenditure but showed lower reproducibility for TEF.