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


METHODS
Six volunteers received a primed, constant, intravenous infusion of [1-13C]acetate at a rate of 1.01 +/- 0.04 micromol x kg(-1) x min(-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 micromol/L and 14.8 +/- 1.4 moles percent excess, respectively. Whole-body acetate turnover was 6.0 +/- 0.7 micromol x kg(-1) x min(-1). After lactulose ingestion, maximum breath hydrogen and acetate concentrations reached 63 +/- 15 ppm (P = 0.004) and 313 +/- 25 micromol/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 micromol x kg(-1) x 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.


CONCLUSIONS
This new method provides a quantitative estimate of colonic carbohydrate fermentation via evaluation of acetate production.
Pouteau
E
E
Centre de Recherche en Nutrition Humaine, Groupe Métabolisme, Nantes, France.
Vahedi
K
K
Messing
B
B
Flourié
B
B
Nguyen
P
P
Darmaun
D
D
Krempf
M
M
D000085:Acetates / Q000032:analysis / Q000378:metabolism*; D000328:Adult; D001419:Bacteria / Q000378:metabolism*; D001944:Breath Tests; D002247:Carbon Isotopes; D003106:Colon / Q000382:microbiology*; D005227:Fatty Acids / Q000097:blood; D005285:Fermentation; D006801:Humans; D006859:Hydrogen / Q000032:analysis; D007700:Kinetics; D007792:Lactulose / Q000378:metabolism*; D008297:Male; D008697:Methane / Q000032:analysis
D000085:Acetates; D002247:Carbon Isotopes; D005227:Fatty Acids; D007792:Lactulose; D006859:Hydrogen; D008697:Methane