PURPOSE: Previous approaches using body-worn devices to measure free-living daily EE in humans using direct calorimetry have been limited by the inability to accurately measure evaporative heat loss. The Personal Calorie Meter (PCM) is a device that uses a heat flow gauge embedded in a permeable membrane, permitting the measurement of both dry and evaporative heat loss. Total heat flux and estimated body surface area are then used to estimate minute by minute EE. In this ongoing study, we are comparing daily EE measured using the PCM with simultaneous measurements using whole-room indirect calorimetry (WRC).
METHODS: Subjects were studied on two separate days under low and high physical activity levels (PAL, ~1.4 and 1.7 x resting metabolic rate, respectively) in the WRC. During the low PAL condition, subjects performed 20 minutes of various housecleaning activities. During the high PAL condition, subjects performed 30 minutes of walking on a treadmill, 30 minutes of stationary cycling, and resistance exercises using dumbbells. Daytime EE was calculated as the total EE from the time the subject entered the WRC until bedtime.
RESULTS: 14 subjects (10 F/4 M, 44±18 yrs., body mass index=26±6 kg.m2, mean±SD) have completed at least one study visit in the room calorimeter. During the low PAL condition (N=11), average daytime EE measured by the PCM (1369±220 kcal, mean±SD) did not differ from WRC (1304±757 kcal), but the range of intra-individual differences was large (-899 to +452 kcal). Five measurements were within ±150 kcal, and the minute-to-minute values corresponded closely in these cases. During the high PAL condition (N=9), average daytime EE measured by the PCM (1834±344 kcal) did not differ from WRC (1880±757 kcal), but there was a wider range of intra-individual differences than during the low PAL condition (-1188 to +1075 kcal).
CONCLUSION: These preliminary data demonstrate the feasibility of measuring EE in humans using portable direct calorimetry. Further studies and refinements are needed to improve the accuracy of the PCM on an individual level.