Measurement of 24-hour Continuous Human CH4 Release in a Whole Room Indirect Calorimeter

We describe the technology and validation of a new whole room indirect calorimeter (WRIC) methodology to quantify methane (CH4) released from the human body over 24h concurrently with the assessment of energy expenditure and substrate utilization. The new system extends the assessment of energy metabolism by adding CH4, a downstream product of microbiome fermentation that could contribute to energy balance. MethodsOur new system consists of an established whole room indirect calorimeter WRIC combined with the addition of off-axis integrated-cavity output spectroscopy (OA-ICOS) to measure CH4 concentrations ([CH4]). The volume of CH4 released (VCH4) was calculated after measuring air flow rates. Development and validation included environmental experiments to measure the stability of the atmospheric [CH4], infusing CH4 into the WRIC and cross-validation studies comparing [CH4] quantified by OA-ICOS and mid-infrared dual-comb spectroscopy (MIR DCS). Reliability of the whole system is reported between years, weeks, days, and validated CH4 infusions. The cross-validation and reliability of VCH4 released from the human body was determined in 19 participants on consecutive days. In addition, we describe a postprocessing analytical method to differentiate CH4 released from breath versus intestine by matching times of stool production and contemporaneous VCH4 release. ResultsOur infusion data indicated that the system measured 24h [CH4] and VCH4 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). Initial human data revealed 24h VCH4 was highly variable between subjects and within / between days; this highlights the importance of a 24-h continuous assessment to have a complete picture of VCH4 release. Finally, our method to quantify VCH4 released by breath or colon suggested that over 50% of the CH4 was eliminated through the breath. ConclusionsThe method allows, for the first time, measurement of 24h VCH4 (in kcal) and therefore the measurement of the proportion of human energy intake fermented to CH4 by the gut microbiome and released via breath or directly from the intestine. Our method is accurate, valid, and will provide meaningful data to understand not only interindividual variation, but also allows us to track the effects of dietary, probiotic, bacterial and fecal microbiota transplantation on VCH4.