Effect of colonic fermentation on respiratory gas exchanges measured in the postabsorptive state

To assess the effect of colonic fermentation on respiratory gas exchanges, six methane-nonproducing healthy volunteers ingested in the postabsorptive state 1 wk apart either 90 mL lactulose syrup containing 60 g lactulose, 4 g lactose, and 7 g galactose or the same solution but without lactulose (control solution). Six patients with short bowel and remnant colon (SBS) also ingested 90 mL lactulose syrup. Carbon dioxide production (VCO2), oxygen consumption (VO2), respiratory quotient (RQ), and hydrogen excreted in breath were measured basally and for 4 h after the ingestion of solutions. In healthy volunteers within 4 h after ingestion of the control solution, VCO2 and the RQ decreased whereas VO2 remained unchanged. In contrast, in healthy volunteers and patients with SBS, VCO2 and the RQ increased after lactulose ingestion, whereas VO2 did not change. The increase in VCO2 appeared to be accounted for mainly by bacterial production of carbon dioxide and was significantly related to breath-hydrogen concentration (r = 0.56, P < 0.02 for healthy subjects; r = 0.59, P < 0.01 for SBS subjects). A breath-hydrogen test should be performed in conjunction with indirect calorimetry to determine whether colonic fermentation is taking place and, if so, to correct appropriately the VCO2 value in calorimetric equations.