Low-Fiber Diet May Drive Gut Microbes to Consume the Intestinal Lining: Study

Plant foods may influence gut health in ways that go beyond their fiber content, with new research highlighting the potential importance of certain indigestible plant proteins.

Two studies led by researchers at Princeton University found that plant fiber and a group of indigestible plant proteins, described as “proteins imitating fiber” or Prif, can alter gut microbial activity and shift the production of metabolites linked to health.

Published in Proceedings of the National Academy of Sciences, one study examined phenol metabolites produced when gut bacteria break down amino acids. Some, including phenylpropionate and hippuric acid, have been associated with healthier metabolic outcomes, while others, such as p-cresol sulfate and phenol sulfate, have been linked to toxicity and poorer health outcomes.

Researchers found that fiber and Prif worked together to favor the production of beneficial phenols while reducing harmful ones. Fiber appeared to limit bacterial breakdown of the gut's mucus lining, while Prif provided microbes with more indigestible dietary protein to process.

The findings suggest that these plant proteins could represent an overlooked component of a healthy diet. Researchers said they may eventually deserve attention alongside fiber when evaluating the nutritional benefits of plant-based foods.

A second study, published in Nature Metabolism, challenged another long-standing assumption: that phenol and indole metabolites circulating in the body are produced exclusively by gut bacteria. Using isotope tracing in animals and human cells, researchers found that mammalian metabolism can also produce several of these compounds.

Some metabolites remained at high levels even after antibiotics disrupted the gut microbiome, supporting the role of the body's own metabolism. In contrast, metabolites produced exclusively by bacteria declined following antibiotic treatment.

Together, the studies provide new insight into how plant foods, gut bacteria and human metabolism interact. The findings could eventually help scientists develop more precise dietary and microbiome-based strategies for preventing or managing disease, although further research is needed to determine whether the effects seen in experimental models translate directly to human health.

REFERENCE:

1.Jenna E. AbuSalim, et al.; Digestion-resistant proteins support the healthy metabolite profiles associated with plant-based diets. Proceedings of the National Academy of Sciences, 2026; 123 (32) DOI: 10.1073/pnas.2605226123

2.Jenna E. AbuSalim, et al.; Host metabolism can produce many indoles and phenols independently of the microbiome. Nature Metabolism, 2026; 8 (7): 1528 DOI: 10.1038/s42255-026-01550-8