biostudies-literatureUnknown9(1)Fernandez-Calleja JMSIndirect calorimetry (InCa) estimates whole-body energy expenditure and total substrate oxidation based on O₂ consumption and CO₂ production, but does not allow for the quantification of oxidation of exogenous substrates with time. To achieve this, we incorporated ¹³CO₂ and ¹²CO₂ gas sensors into a commercial InCa system and aimed to demonstrate their performance and added value. As a performance indicator, we showed the discriminative oscillations in ¹³CO₂ enrichment associated with food intake in mice fed diets containing naturally low (wheat) vs high (maize) ¹³C enrichment. To demonstrate the physiological value, we quantified exogenous vs total carbohydrate and fat oxidation continuously,Scientific reports11507https://www.ebi.ac.uk/biostudies/studies/S-EPMC6687832biostudies-literatureExtended indirect calorimetry with isotopic CO₂ sensors for prolonged and continuous quantification of exogenous vs. total substrate oxidation in mice.PMC6687832Swarts HJMFernandez-Calleja JMSBouwman LMSOosting AKeijer Jvan Schothorst EMfalseExtended indirect calorimetry with isotopic CO₂ sensors for prolonged and continuous quantification of exogenous vs. total substrate oxidation in mice.Indirect calorimetry (InCa) estimates whole-body energy expenditure and total substrate oxidation based on O₂ consumption and CO₂ production, but does not allow for the quantification of oxidation of exogenous substrates with time. To achieve this, we incorporated ¹³CO₂ and ¹²CO₂ gas sensors into a commercial InCa system and aimed to demonstrate their performance and added value. As a performance indicator, we showed the discriminative oscillations in ¹³CO₂ enrichment associated with food intake in mice fed diets containing naturally low (wheat) vs high (maize) ¹³C enrichment. To demonstrate the physiological value, we quantified exogenous vs total carbohydrate and fat oxidation continuously,2019-01-01T00:00:00Z2019 Aug2025-05-29T22:10:25.353Z2025-05-29T22:10:25.353ZS-EPMC66878323139591610.1038/s41598-019-47977-w