When dietary fiber runs low, some microbes in your gut may switch food sources.
They begin breaking down proteins in the mucus layer that shields the intestinal wall.
The mucus lining is more than a slick coating. It is the buffer that keeps trillions of gut bacteria at arm's length from the sensitive cells beneath. When bacteria erode it, the barrier thins, opening the door to inflammation and easier access for pathogens.
A widely cited 2016 study in Cell first laid out the mechanism in mice. Within days of switching animals to a fiber-free diet, gut microbes turned to the host's own mucus glycoproteins as a nutrient source.
Also read: How much should you be able to overhead press? The standards by age and sex
The colonic barrier eroded, and the animals became more vulnerable to a gut pathogen.
Why the mucus layer matters
The new Ludwig Princeton work, published in the Proceedings of the National Academy of Sciences and Nature Metabolism, pushes the story further.
The team labeled dietary proteins with stable isotopes and tracked the phenolic compounds circulating in the blood after digestion.
Harmful phenols such as p-cresol sulfate came from bacteria feeding on the host's own gut mucus. Beneficial phenols were produced almost entirely from indigestible plant proteins, which the researchers call "proteins imitating fiber," or Prif.
Also read: Is breakfast really the most important meal? Here's what the evidence actually says
The takeaway from both studies is that fiber and certain plant proteins can shift the microbiome's metabolic output in a healthier direction. Fiber, in short, appears to keep the microbes fed and off the gut lining.
Foods that keep the barrier fed
Reaching the target does not require a diet overhaul.
A single cup of raspberries carries about 8 grams of fiber, according to Cleveland Clinic. Two tablespoons of chia seeds add another 10 grams.
A half-cup of cooked black beans delivers roughly 8.5 grams, lentils and split peas about 8 grams, and chickpeas about 6.5 grams.
Also read: Plant protein vs. animal protein: which is better for your heart and muscles?
A medium pear brings 5.5 grams, a cup of cooked oats about 5.5 grams, and a medium apple about 4.5 grams.
Experts have long recommended a daily intake of 25 to 38 grams of fiber for adults.
Anyone increasing fiber sharply is generally advised to add it gradually and drink more water, because a sudden jump can cause bloating and gas.
People with inflammatory bowel disease or other digestive conditions should talk to a doctor before major shifts, since fiber tolerance varies and some conditions require tailored dietary guidance.
Also read: How eating turmeric every day may affect your joints, heart and brain
Also read: Cognitive decline is not inevitable: your brain may keep improving at any age
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.