Summary
This study elucidates how dietary fibre shapes gut microbial tryptophan metabolism through metabolic interactions rather than simple abundance effects. Using defined three-species bacterial communities and complex human faecal cultures, the authors demonstrated that fibre-degrading Bacteroides thetaiotaomicron cross-feeds monosaccharides to other bacteria, triggering catabolite repression that inhibits indole production and redirects tryptophan towards health-protective indolelactic and indopropionic acids. The findings provide mechanistic explanation for why fermentable fibre consumption suppresses potentially harmful indole whilst promoting beneficial tryptophan metabolites.
Regional applicability
The findings are internationally relevant and applicable to United Kingdom populations and dietary recommendations. The mechanism is demonstrated at the fundamental microbial level and should apply across populations consuming variable fibre intakes, supporting evidence-based public health messaging on fermentable fibre benefits in the UK context.
Key measures
Production of tryptophan-derived metabolites (indole, ILA, IPA); bacterial abundance and metabolic pathway regulation; competition for tryptophan substrate among defined microbial communities
Outcomes reported
The study identified mechanisms by which dietary fibre influences gut microbial tryptophan metabolism, directing it away from indole (associated with chronic kidney disease) and towards protective indolelactic acid (ILA) and indopropionic acid (IPA). The work demonstrated that fibre-degrading bacteria affect this competition through cross-feeding of metabolic substrates rather than direct abundance effects.
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