Influence of long-term administration of lactulose and Saccharomyces boulardii on the colonic generation of phenolic compounds in healthy human subjects

J Am Coll Nutr. 2006 Dec;25(6):541-9. doi: 10.1080/07315724.2006.10719570.


Objective: Proteins are degraded in the colon by bacterial fermentation into potentially toxic metabolites such as phenolic compounds. The aim of the present study was to investigate whether long-term administration of lactulose or Saccharomyces boulardii cells would result in a lower protein degradation. In addition, the influence of a long-term dietary intake on different gastrointestinal parameters was investigated.

Methods: The effect of long-term intervention of the substrates was evaluated in a randomized, cross-over study in 43 healthy volunteers. At the start of the study and at the end of each 4-week treatment period, urine was collected during 48 h in different fractions and faeces during 72 h. Breath test samples and blood samples were taken to study gastrointestinal parameters.

Results: No influence of long-term administration of both substrates was found on GE, OCTT and serum lipids. A significant decrease in small intestinal permeability was found after long-term dietary intervention with lactulose. Long-term administration of lactulose significantly decreased urinary p-cresol excretion, but did not lower fecal p-cresol excretion. No significant effects were observed after S. boulardii intake.

Conclusion: The results obtained in present study have indicated that colonic amino acid fermentation can be reduced by the administration of lactulose as a fermentable carbohydrate.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Amino Acids / metabolism*
  • Breath Tests
  • Colon / metabolism*
  • Colon / microbiology
  • Colony Count, Microbial
  • Cresols / metabolism
  • Cresols / urine
  • Cross-Over Studies
  • Dose-Response Relationship, Drug
  • Feces / chemistry
  • Female
  • Fermentation
  • Gastric Emptying / drug effects
  • Gastrointestinal Agents / administration & dosage
  • Gastrointestinal Agents / metabolism
  • Gastrointestinal Transit
  • Humans
  • Lactulose / administration & dosage*
  • Lactulose / metabolism*
  • Male
  • Permeability
  • Saccharomyces / metabolism*


  • Amino Acids
  • Cresols
  • Gastrointestinal Agents
  • 4-cresol
  • Lactulose