Scientists show: without fiber, gut bacteria start eating the protective mucus

Bacteria switch to mucus

Gut bacteria deprived of fiber begin to break down the protective mucus of the intestine and produce harmful compounds in the process. Researchers reported this at the Princeton branch of the Ludwig Institute for Cancer Research; the results were published in the journal Proceedings of the National Academy of Sciences.

Harmful and beneficial phenols

We are talking about phenolic metabolites — substances that bacteria create by processing amino acids. From tyrosine, microbes make p-cresol sulfate and phenol sulfate: these compounds have been linked to severe cancer progression and harm in kidney disease. From phenylalanine, by contrast, come the beneficial phenylpropionate and hippuric acid, which are associated with a healthy weight and a strong gut.

What the experiments showed

Isotope-labeling experiments in mice showed that bacteria take the raw material for harmful phenols from the body's own proteins — primarily from the mucus that lines the intestine and protects its walls from microbes. Beneficial phenols are produced almost entirely from indigestible food proteins. Fiber keeps bacteria from destroying the mucus, while plant proteins that pass through digestion 'untouched' provide them with a satisfying alternative. The authors called such proteins prifs — fiber-mimicking proteins.

The authors' assessment

'Prifs are a new class of food substances that shape the composition of the gut microbiome and can significantly affect metabolic health,' said the study's first author, Jenna Abu Salim. The study's lead, Joshua Rabinowitz, added that one day prif content may appear on food packaging — a line below fiber. This remains a statement about a possible prospect, not an adopted decision.

Some 'bacterial' metabolites are made by the body itself

A parallel study by the same team in the journal Nature Metabolism changes ideas about the origin of gut metabolites. Isotope labels in mice, rats and human cells showed that many compounds, such as indole-3-lactate and indole-3-acetate, are synthesized by the body itself, without microbes. After a course of antibiotics, their levels in the blood of mice and patients remained high — only substances that only bacteria can make declined. This means that plans to manage the body's chemistry through diets and probiotics will have to be reconsidered: some compounds are easier to regulate within the body itself.

Limitations and context

The authors note that most of the data was obtained in animals and cells, so practical recommendations for humans are still far off. Earlier, in October, Gazeta.Ru reported on another related finding — a discovered way to destroy dangerous gut bacteria without harming beneficial ones; the new work on prifs and metabolites neither supersedes nor directly builds on it.