A system for contact free energy expenditure assessment under free-living conditions: monitoring metabolism for weight loss using carbon dioxide emission

Weight disorders are strikingly prevalent globally and can contribute to a wide array of potentially fatal diseases spanning from type II diabetes to coronary heart disease. These disorders have a common cause: poor calorie balance. Since energy expenditure (EE) (kcal d(-1)) constitutes one half of the calorie balance equation (the other half being food intake), its measurement could be of great value to those suffering from weight disorders. A technique for contact free assessment of EE is presented, which only relies on CO2 concentration monitoring within a sealed office space, and assessment of carbon dioxide production rate (VCO2). Twenty healthy subjects were tested in a cross-sectional study to evaluate the performance of the aforementioned technique in measuring both resting EE (REE) and exercise EE using the proposed system (the 'SmartPad') and a U.S. Food and Drug Administration (FDA) cleared gold standard reference instrument for EE measurement. For VCO2 and EE measurements, the method showed a correlation slope of 1.00 and 1.03 with regression coefficients of 0.99 and 0.99, respectively, and Bland-Altman plots with a mean bias = -0.232% with respect to the reference instrument. Furthermore, two subjects were also tested as part of a proof-of-concept longitudinal study where EE patterns were simultaneously tracked with body weight, sleep, stress, and step counts using a smartwatch over the course of a month, to determine correlation between the aforementioned parameters and EE. Analysis revealed moderately high correlation coefficients (Pearson's r) for stress (r(average) = 0.609) and body weight (r(average) = 0.597) for the two subjects. The new SmartPad method was demonstrated to be a promising technique for EE measurement under free-living conditions.