Production rate of acetate during colonic fermentation of lactulose: A stable-isotope study in humans

Abstract

Background: Breath tests are currently used to qualitatively assess colonic fermentation; no quantitative estimations are available for healthy subjects. Objective: This study describes a stable-isotope-dilution method to measure acetate production quantitatively from colonic bacterial fermentation. Design: Six volunteers received a primed, constant, intravenous infusion of [1-13]acetate at a rate of 1.01 ± 0.04 μmol · kg-1 for 7 h. They ingested 20 g pure lactulose after 1 h of the tracer infusion. Expired air and arterialized venous blood were sampled every 15 min. Results: Before lactulose intake, the breath-hydrogen concentration was 7 ± 2 ppm and the plasma acetate concentration and isotopic enrichment were 141 ± 14 μmol/L and 14.8 ± 1.4 moles percent excess, respectively. Whole-body acetate turnover was 6.0 ± 7.0 μmol · kg-1 · min-1. After lactulose ingestion, maximum breath hydrogen and acetate concentrations reached 63 ± 15 ppm (P = 0.004) and 313 ± 25 μmol/L (P = 0.002), respectively, whereas [13C]acetate enrichment decreased to 9.9 ± 1.3 moles percent excess (P = 0.03). Whole-body acetate turnover increased to 9.8 ± 1.5 μmol · kg-1 · min-1 and later decreased almost to baseline values. Colonic lactulose fermentation yielded 140 ± 12 mmol acetate over 6 h, representing 86% of the production based on stoichiometric equations. Conclusion: This new methods provides a quantitative estimate of colonic carbohydrate fermentation via evaluation of acetate production.