Measurement of 24-h continuous human CH 4 release in a whole room indirect calorimeter.

We describe the technology and validation of a new whole room indirect calorimeter (WRIC) methodology to quantify volume of methane (VCH 4 ) released from the human body over 24 h concurrently with the assessment of energy expenditure and substrate utilization. The new system extends the assessment of energy metabolism by adding CH 4 , a downstream product of microbiome fermentation that could contribute to energy balance. Our new system consists of an established WRIC combined with the addition of off-axis integrated-cavity output spectroscopy (OA-ICOS) to measure CH 4 concentration ([CH 4 ]). Development, validation, and reliability of the system included environmental experiments to measure the stability of the atmospheric [CH 4 ], infusing CH 4 into the WRIC and human cross-validation studies comparing [CH 4 ] quantified by OA-ICOS and mid-infrared dual-comb spectroscopy (MIR DCS).Our infusion data indicated that the system measured 24-h [CH 4 ] and VCH 4 with high sensitivity, reliability, and validity. Cross-validation studies showed good agreement between OA-ICOS and MIR DCS technologies (r = 0.979, P < 0.0001). Human data revealed 24-h VCH 4 was highly variable between subjects and within/between days. Finally, our method to quantify VCH 4 released by breath or colon suggested that over 50% of the CH 4 was eliminated through the breath. The method allows, for the first time, measurement of 24-h VCH 4 (in kcal) and therefore the measurement of the proportion of human energy intake fermented to CH 4 by the gut microbiome and released via breath or from the intestine; also, it allows us to track the effects of dietary, probiotic, bacterial, and fecal microbiota transplantation on VCH 4 . NEW & NOTEWORTHY This is the first time that continuous assessment of CH 4 is reported in parallel with measurements of O 2 consumption and CO 2 production inside a whole room indirect calorimeter in humans and over 24 h. We provide a detailed description of the whole system and its parts. We carried out studies of reliability and validity of the whole system and its parts. CH 4 is released in humans during daily activities.