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.