Effect of lactulose and Saccharomyces boulardii administration on the colonic urea-nitrogen metabolism and the bifidobacteria concentration in healthy human subjects

Background Protein fermentation products, especially ammonia, are implicated in the pathogenesis of certain diseases. Aim To investigate the influence of lactulose and Saccharomyces boulardii cells on the composition of the intestinal microbiota and on the metabolic fate of ammonia by means of lactose-[N-15, N-15]-ureide. Methods An at random, placebo-controlled, crossover study was performed in 43 healthy volunteers to evaluate the influence of lactulose and/or S. boulardii cells either administered as a single dose or after a 4-week intake period. Urine and faeces were collected. All samples were analysed for N-15-content by combustion-isotope ratio mass spectrometry. Real- time polymerase chain reaction was applied to determine the composition of the predominant faecal microbiota. Results A single administration of lactulose significantly decreased urinary N-15-excretion in a dose-dependent way. After long-term administration of lactulose, a significant reduction of the urinary N-15-excretion was observed, which was accompanied with a significant increase in the faecal N-15-output, more specifically more N-15 was found in the bacterial fraction. A significant rise in the Bifidobacterium population was found after lactulose intake. No significant effects were observed after S. boulardii intake. Conclusion Dietary addition of lactulose can exert a bifidogenic effect accompanied by a favourable effect on the colonic NH3-metabolism.