A human volunteer study to determine the prebiotic effects of lactulose powder on human colonic microbiota

Abstract

The prebiotic effects of lactulose were monitored in a human feeding study. Prebiotics are dietary carbohydrates that have a selective microbial metabolism in the gut, directed towards bacteria seen as beneficial, examples being bifidobacteria and/or lactobacilli. The study was conducted in a double blind, placebo controlled manner. A dose of 10 g per day, half the pharmacological dose, was fed to 10 healthy adult volunteers. In parallel, 10 persons were fed a placebo (glucose/lactose). Both culture based methodologies and genetic probing, based around fluorescent in situ hybridization were used to determine bacterial populations. Faecal water genotoxicity was assessed using the Comet assay to investigate the ability of lactulose to protect against DNA damage. Bifidobacteria showed a statistically significant increase during lactulose intake, whilst genetic probing showed a concomitant decrease in clostridia. Viable plate counts of lactobacilli increased when lactulose was fed, but this was not replicated by the genetic probing. During the trial, none of the recruits experienced any significant adverse gastrointestinal symptoms. Single-cell gel electrophoresis, used to assess faecal water genotoxicity, did not reveal that lactulose intervention reduced genotoxicity. The prebiotic nature of 10 g/day lactulose towards the human gut microbiota has been clearly demonstrated in this study. Lactulose is shown to be an effective food-grade prebiotic for healthy adults particularly in sections of the community with low bifidobacterial populations. The value of the more direct, culture independent FISH technique in the microbial ecology of the gut has been demonstrated in this study.