Xiaojun Xian, Ashley Quach, Devon Bridgeman, Francis Tsow*, Erica Forzani* and Nongjian Tao*
Center for Bioelectronics & Biosensors, the Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA
Received: 30 October, 2014; Accepted: 25 March, 2015; Published: 29 March, 2015
Francis Tsow, Center for Bioelectronics & Biosensors, the Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA, Email:
Erica Forzani, Center for Bioelectronics & Biosensors, the Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA, Email:
Nongjian Tao, Center for Bioelectronics & Biosensors, the Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA, Email:
Xian X, Quach A, Bridgeman D, Tsow F, Forzani E, et al. (2015) Personalized Indirect Calorimeter for Energy Expenditure (EE) Measurement. Glob J Obes Diabetes Metab Syndr 2(1): 004-008. DOI: 10.17352/2455-8583.000007
© 2015 Xian X, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Indirect calorimetry; Metabolism tracker; Energy expenditure; Respiratory quotient
Background and aims: A personal indirect calorimeter allows everyone to assess resting and non-resting energy expenditure, thus enabling accurate determination of a person's total calorie need for weight management and fitness. The aim of this study is to compare the performance of a new personal metabolic rate tracker based on indirect calorimetry, Breezing®, with the Douglas bag method, the gold standard method for energy expenditure (EE) measurement.
Methods: Energy expenditures (EE) at rest and during activities, and respiratory quotient (RQ) were measured for 12 healthy subjects, including 7 male and 5 female under different living conditions. A total of 314 measurements were performed with Breezing®, and the results were compared with those by the Douglas bag method.
Results: R-squared correlation coefficients (R2) between the data obtained with Breezing® and the Douglas bag method were 0.9976, 0.9986, 0.9981, and 0.9980, for VO2, VCO2, EE, and RQ respectively.
Conclusions: The EE and RQ values determined by Breezing® are in good agreement with those by the Douglas bag method.
A person's resting energy expenditure (REE) is his/her energy expenditure under resting conditions, which is the minimal need of energy to sustain life. During physical activities, the energy expenditure (EE) will be higher, depending on the type, intensity and duration of each physical activity. Indirect calorimetry is the most well established approach for accurate assessment of REE and EE, and widely used in clinical and fitness labs for nutritional support, exercise recommendation, and weight management [1Pinheiro Volp AC, Esteves de Oliveira FC, Duarte Moreira Alves R, Esteves EA, Bressan J (2011) Energy expenditure: components and evaluation methods. Nutr Hosp 26: 430-440.,2Ferrannini E (1988) The theoretical bases of indirect calorimetry: a review. Metabolism 37: 287-301.]. However, traditional indirect calorimetry equipment is bulky, expensive, and complicated to calibrate and use. For this reason, equations have been created to estimate REE. Because REE depends on age, gender, genes and other attributes of the person, which thus varies widely from person to person, the estimated REE using the well known Harris-Benedict equation [3Harris JA, Benedict FG (1918) A biometric study of human basal metabolism. Proc Natl Acad Sci U S A. 4: 370-373.] or improved equations4 can be significantly different from the person's true REE value. Additionally, a person's REE may vary over time. For example, exercise may increase REE, and reduction of calorie intake may decrease REE [5Leibel RL, Rosenbaum M, Hirsch J (1995) Changes in energy expenditure resulting from altered body weight. N Engl J Med 332: 621-628.,6Nelson KM, Weinsier RL, Long CL, Schutz Y (1992) Prediction of resting energy expenditure from fat-free mass and fat mass. Am J Clin Nutr 56: 848-856.]. To fulfill the needs, a mobile indirect calorimeter, Breezing® was developed to facilitate personalized REE measurement and tracking. This pocket-sized indirect calorimeter measures oxygen consumption rate (VO2) and carbon dioxide production rate (VCO2) in breath with a colorimetric technology, from which REE and EE are determined according to the well-known Weir equation [7Weir JB (1949) New methods for calculating metabolic rate with special reference to protein metabolism. J Physiol 109: 1-9.]. It also measures respiratory quotient (RQ = VCO2/VO2), which is indicative of the source of energy used at the time of the measurement (e.g., carbohydrate vs. fat).
In order to evaluate the accuracy and performance of the mobile indirect calorimeter, a comparative study was carried out using mobile indirect calorimeter and the gold standard Douglas bag method. Over 300 measurements with human objects were performed following the instructions of the mobile indirect calorimeter and standard protocols of the Douglas Bag method. Statistical analysis methods, such as linear regression and Bland-Altman plot were used to establish quantitative correlation between of the values from the mobile indirect calorimeterand that from the gold standard method.
Materials and Methods
Twelve healthy adults from Arizona State University (ASU), including 7 male and 5 female, were tested during this study. Their ages ranged from 21 to 38 years and their body mass indices (BMI) ranged from 16.9 to 32.2kg/m2 (Table 1 and Table 2). The study was approved by the Institutional Review Board of Arizona State University (IRB protocol #1012005855) and all subjects participated in the study voluntarily, providing written informed consent prior to participation. The study was carried out at ASU from January 2013 to June 2014.
The mobile indirect calorimeter, Breezing® Device
The Breezing® device uses a sensor cartridge and a flow meter to determine the rate of consumed oxygen and produced carbon dioxide in the breath. The sensing technology of the new indirect calorimeter, which used a cell-phone camera as the optical detector, was previously reported [8Zhao D, Xian X, Terrera M, Krishnan R, Miller D, et al. (2014) A pocket-sized metabolic analyzer for assessment of resting energy expenditure. Clin Nutr 33: 341-347.]. The current Breezing® device uses a QR code to carry calibration parameters of a single-use sensor cartridge, which can be scanned and recognized by the mobile application (app). The device is 6.0 oz. (170 g), and 1.8 in × 2.1 in × 4.8 in (4.7 cm × 5.4 cm × 12.3 cm), and connects wirelessly to an iOS mobile device, using Bluetooth 4.0 technology.
The mobile device (phone or tablet) receives data from the device, processes information, and then provides test results and summaries through a graphic user interface. It determines the energy expenditure from the measurement of VO2 and VCO2 according to the Weir equation, along with RQ. In addition to the sensor cartridge, the Breezing® device is used with a non-rebreathing 2-valvesmouthpiece, as shown in Figure 1.
- Pinheiro Volp AC, Esteves de Oliveira FC, Duarte Moreira Alves R, Esteves EA, Bressan J (2011) Energy expenditure: components and evaluation methods. Nutr Hosp 26: 430-440 .
- Ferrannini E (1988) The theoretical bases of indirect calorimetry: a review. Metabolism 37: 287-301 .
- Harris JA, Benedict FG (1918) A biometric study of human basal metabolism. Proc Natl Acad Sci U S A. 4: 370-373 .
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- Nelson KM, Weinsier RL, Long CL, Schutz Y (1992) Prediction of resting energy expenditure from fat-free mass and fat mass. Am J Clin Nutr 56: 848-856 .
- Weir JB (1949) New methods for calculating metabolic rate with special reference to protein metabolism. J Physiol 109: 1-9 .
- Zhao D, Xian X, Terrera M, Krishnan R, Miller D, et al. (2014) A pocket-sized metabolic analyzer for assessment of resting energy expenditure. Clin Nutr 33: 341-347 .
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