Indirect calorimetry protocol development for measuring resting metabolic rate as a component of total energy expenditure in free-living postmenopausal women

An objective measure of energy intake is needed in epidemiologic studies to evaluate random and systematic error associated with dietary self-report tools. Total energy expenditure in weight-stable humans is accepted as a measure of energy intake, but doubly labeled water remains cost prohibitive for large studies. Our purpose was to develop a practical indirect calorimetry (IC) protocol for estimating resting metabolic rate (RMR) in free-living, postmenopausal women. We conducted duplicate IC measures 1 wk apart using a canopy system on 102 women ages 50-79 y from the Seattle area. We compared RMR for 0-5, 5-10, 5-15, 5-20, 5-25, 5-30, and 0- to 30-min IC segments and segments meeting stability criteria. The mean RMR for the first 5 min was significantly higher than other time segments (P = 0.001). Correlation coefficients between duplicate measures were high (r = 0.90). Use of defined stability criteria produced RMR measures that were 10-30 kcal (42-126 kJ) higher than the 5- to 10-min RMR measures and 40-60% of subjects did not achieve these stability criteria. For protocols including IC to assess RMR as a component of total energy expenditure in free-living, postmenopausal women, a single 10-min canopy study, excluding the first 5 min of data, produces reliable results with minimal subject burden.