Gut microbes may consume the protective mucus lining of the gut when dietary fiber is scarce. This finding comes from research led by Jenna AbuSalim and Joshua Rabinowitz at Ludwig Princeton. Their studies suggest that both fiber and certain plant proteins can alter microbial metabolism. These changes can increase beneficial compounds while reducing harmful ones.
Two studies, published in *Proceedings of the National Academy of Sciences* and *Nature Metabolism*, explore these interactions. The *PNAS* study found that plant fiber and indigestible plant proteins, termed “proteins imitating fiber” (Prif), shift the balance of phenol metabolites. This shift favors beneficial types derived from phenylalanine over harmful types from tyrosine.
Researchers used stable isotopes to trace proteins in mice. They observed that harmful phenols were produced when bacteria consumed host proteins, such as those in the gut's mucus lining. Beneficial phenols, however, primarily came from indigestible dietary proteins. Fiber reduced the bacterial breakdown of the gut's mucus, decreasing harmful phenol production. Prif increased the amount of dietary protein available to gut microbes, boosting beneficial phenol production.
The *Nature Metabolism* study investigated the origins of phenol and indole metabolites. Scientists previously assumed gut bacteria were the sole producers of these compounds. However, this research showed that mammalian metabolism can also produce many indole and phenol metabolites independently. This includes important compounds like indole-three-lactate and indole-three-acetate.
Circulating levels of these metabolites remained high in mice even after antibiotic treatment disrupted the microbiome. A similar pattern was seen in human patients taking antibiotics. Metabolites exclusively made by microbes, such as indole-three-propionate and p-cresol sulfate, declined after antibiotic treatment. These findings provide a clearer understanding of metabolite origins and how diet interacts with the microbiome.
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