Measurement of 24-h 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 volume of methane (VCH₄) 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 CH₄, 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 CH₄ concentration ([CH₄]). Development, validation, and reliability of the system included environmental experiments to measure the stability of the atmospheric [CH₄], infusing CH₄ into the WRIC and human cross-validation studies comparing [CH₄] quantified by OA-ICOS and mid-infrared dual-comb spectroscopy (MIR DCS).Our infusion data indicated that the system measured 24-h [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). Human data revealed 24-h VCH₄ was highly variable between subjects and within/between days. Finally, our method to quantify VCH₄ released by breath or colon suggested that over 50% of the CH₄ was eliminated through the breath. The method allows, for the first time, measurement of 24-h 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 from the intestine; also, it allows us to track the effects of dietary, probiotic, bacterial, and fecal microbiota transplantation on VCH₄. NEW & NOTEWORTHY This is the first time that continuous assessment of CH₄ is reported in parallel with measurements of O₂ consumption and CO₂ 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. CH₄ is released in humans during daily activities.