When gut microbes run low on fiber, they may start eating you

When fiber runs low, gut microbes may start feeding on your protective gut lining instead. Date: August 15, 2026 Source: Ludwig Institute for Cancer Research Summary: Gut microbes need something to eat, and when fiber is limited, they may begin consuming proteins from the mucus lining that protects the gut. Researchers found that fiber can suppress this process, while indigestible plant proteins help microbes produce more beneficial compounds. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY Plant foods may secretly reprogram gut bacteria—and an overlooked type of plant protein could be nearly as important as fiber. Credit: Shutterstock Plant based diets support health in several ways, including benefits for the gut, immune system, metabolism, and cardiovascular system. Part of that effect comes from encouraging a diverse population of bacteria in the intestines. Scientists have long known that dietary fiber contributes to these benefits because gut microbes help break it down. Plants also contain colorful "phytochemicals" that help protect them from environmental threats and may influence human health. Even so, researchers are still working to understand exactly how gut bacteria process the many components of plant foods and how those interactions produce beneficial effects. Two studies led 's Jenna AbuSalim and Director Joshua Rabinowitz offer new insight into that process. One appears in the current issue of the Proceedings of the National Academy of Sciences, while the other was published in Nature Metabolism in June. The first study found that plant fiber and certain plant proteins can change microbial metabolism in ways that increase beneficial metabolites while reducing harmful ones. The second showed that several biologically important metabolites usually credited to gut microbes can also be produced in substantial amounts . "There's growing interest across medical disciplines in manipulating the human microbiome or using its metabolic products themselves for therapy," said Rabinowitz. "Diet holds great promise for controlling the microbiome and its outputs. But to devise effective therapeutic interventions, we need to understand what aspects of the diet control which microbial outputs." How Plant Foods Shift Gut Metabolites In the PNAS study, Rabinowitz, AbuSalim and their colleagues examined how plant based foods influence phenol metabolites. Gut bacteria create these compounds when they digest the amino acids tyrosine and phenylalanine, but the resulting metabolites can have very different effects on health. Phenylpropionate and hippuric acid are produced when bacteria process phenylalanine, and they are associated with gut health and healthy body weight. By contrast, p-cresol sulfate and phenol sulfate come from tyrosine and have been linked to worse outcomes in cancer patients as well as systemic toxicity in people with kidney disease. "Our studies showed that both the fiber and indigestible proteins from plants -- which we call 'proteins imitating fiber,' or Prif -- shift the balance of phenol metabolites from the harmful kind made from tyrosine to the healthful variety derived from phenylalanine," said AbuSalim.