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Summary

Background  Dietary intervention with prebiotics can cause changes in the colonic microbiota and their metabolic activities.

Aim  To investigate whether the response to prebiotic dosing is influenced by the baseline metabolic activity of the colonic flora and bifidobacteria counts.

Methods  The 4-week effect of lactulose (10 g bid.; n = 29) and oligofructose-enriched inulin (10 g bid.; n = 19) was evaluated in healthy human volunteers. Lactose-[15N, 15N]-ureide was used to study the colonic NH3-metabolism. Urine (48 h) and faeces (72 h) were collected and analysed for p-cresol and 15N-content by gas chromatography–mass spectrometry and isotope ratio mass spectrometer, respectively. Faecal bifidobacteria were quantified by real-time polymerase chain reaction.

Results  After the 4-week prebiotic administration period, the urinary excretion of p-cresol and 15N was significantly decreased in both groups (P < 0.05) corresponding to a significantly higher faecal excretion of 15N (P < 0.05). The decrease in urinary 15N and p-cresol excretion significantly correlated with baseline 15N and p-cresol levels (P < 0.05), indicating that subjects with higher baseline levels showed a higher response to prebiotic dosing. Furthermore, a significant correlation was seen between baseline bifidobacteria counts and the effect of prebiotic intake (P < 0.05).

Conclusion  The response to prebiotic dosing, as indicated by the fate of NH3, p-cresol and bifidobacteria, is determined by the initial colonic conditions.