Citation: Mora SJ, Mann S, Bridgeman D, Quach A, Xian X, et al. (2020) Validation of a wearable metabolic tracker (Breezing Pro TM ) for Resting Energy Expenditure (REE) measurement via Douglas bag method. Glob J Obes Diabetes Metab Syndr 7(1): 001-008. DOI: https://dx. IntroductionResting Energy Expenditure (REE), also called Resting Metabolic Rate (RMR), has been widely used for fi tness, nutrition and diseases study due to its high importance to body energy balance [1][2][3][4][5][6]. REE is the major component of the Total Energy Expenditure (TEE), determined by basal energy expenditure, diet induced thermogenesis and physical activity Abstract Background and aims: Resting Energy Expenditure (REE) is one of the most important metabolic parameters since it accounts for 60%-70% of total energy expenditure (TEE) in a typical population and 80%-90% in a sedentary one. Accurate measurement of REE is essential for weight control, nutrition management, and disease treatment. Though metabolic carts, desktop metabolic analyzers, and portable metabolic trackers are available on the market to address certain needs of metabolic rate measurement, a stand-alone and truly wearable metabolic tracker that can provide comfortable and natural breathing experience (e.g. lacking of nose clips and mouthpieces) for nasal and pulmonary disease-restricted users is preferred. Here is featured a novel, wearable, stand-alone and fully integrated metabolic analyzer that overcomes the abovementioned user experience barriers. The Breezing Pro TM determines REE based on the indirect calorimetry method. It measures both oxygen consumption (VO 2 ) and carbon dioxide production (VCO 2 ) rates using integrated colorimetric sensing technology. This work evaluates the accuracy of Breezing Pro TM device against the Douglas bag method, considered the gold standard of indirect calorimetry, and validates its functions as the world's fi rst wearable and fully-integrated metabolic tracker, without the need for wearable accessories such as detector back packs, holders, and shoulder straps compared to other predecessors. Methods:A total of 66 healthy subjects under resting conditions were simultaneously tested by Breezing Pro TM and the Douglas bag method. The exhalation rate (V E ), VO 2 , VCO 2 , and REE results from both methods were compared to evaluate the performance of the Breezing Pro TM device. Results:The comparative correlation plots for V E , VO 2 , VCO 2 , and REE indicate a strong correlation between the two methods for measuring the metabolic parameters previously described. R-squared correlation coeffi cients (R 2 ) between the data obtained were close to 0.9 for all parameters. Conclusions:The accuracy of Breezing Pro TM for measuring V E , VO 2 , VCO 2 and REE has been validated using the gold standard Douglas Bag method. The results indicate that Breezing Pro TM is reliable for resting metabolic parameters measurements.