People who eat foods with too little fiber are at risk of developing gut infection, a new study says. The authors say this happens because when the bacteria present in the gut doesn’t have enough fiber to feed on, it begins munching on the natural layer of mucus that lines the gut, promoting bacterial invasion, inflammation and infection.
The study, “A Dietary Fiber-Deprived Gut Microbiota Degrades The Colonic Mucus Barrier And Enhances Pathogen Susceptibility,” was published in the journal Cell.
“Despite the accepted health benefits of consuming dietary fiber, little is known about the mechanisms by which fiber deprivation impacts the gut [bacteria] and alters disease risk,” the authors wrote.
Researchers transplanted 14 bacteria that grow in the human gut to mice that have no gut bacteria of their own to study what would happen to these animals when they were given either a fiber-enriched or a fiber-free diet.
In a normal gut, the mucus layer is constantly being produced and degraded. But if there is a change in the growth levels of gut bacteria, this important equilibrium is affected.
They found that mice on a fiber-enriched diet (15 percent fiber from minimally processed grains and plants) presented a thick mucus layer, and bacteria did not cause any infection. However, when mice were given a fiber-free diet, the mucus layer started to become thinner just a few days later.
Also, prebiotic fiber (a type of non-digestible fiber found in some processed foods and supplements) induced similar effects in mice of a degraded mucus layer as a fiber-free diet.
The mix of bacteria in the mice gut varied according to the type of diet they were given – some bacteria species reproduced and grew more in low-fiber conditions, but others seemed to prefer high-fiber conditions.
The bacteria that grew more in low- or no-fiber conditions were those that produced several enzymes responsible for the breakdown of the mucus layer components. Indeed, more than 1,600 enzymes capable of degrading carbohydrates were identified in the study, showing a level of complexity similar to that observed in the normal human gut.
Researchers also analyzed mice infected with Citrobacter rodentium, a bacteria that has similar effects to those of E. coli in humans, such as gut infection leading to irritation, inflammation and diarrhea. C. rodentium flourished more with a fiber-free diet, causing weight loss and gut tissue inflammation in the infected mice. The mice that received a fiber-enriched diet before being infected also presented signs of inflammation, but in a much smaller area of their gut.
“The lesson we’re learning from studying the interaction of fiber, gut microbes and the intestinal barrier system is that if you don’t feed them, they can eat you,” Eric Martens, PhD, the study’s senior author, said in a news release.
These results also suggest the potential of using fiber to reverse the effects of digestive tract disorders.
The team wants to study the effect of different mixes of prebiotic fiber and of diets with intermittent natural fiber content over a longer period, as well as identify biomarkers that can be used to assess the status of the gut mucus layer by, for example, indicating the abundance of certain bacteria strains.
They also want to study the impact of a low-fiber diet on chronic diseases, such as inflammatory bowel disease (IBD).
“While this work was in mice, the take-home message from this work for humans amplifies everything that doctors and nutritionists have been telling us for decades: Eat a lot of fiber from diverse natural sources,” Martens said. “Your diet directly influences your microbiota, and from there it may influence the status of your gut’s mucus layer and tendency toward disease. But it’s an open question of whether we can cure our cultural lack of fiber with something more purified and easy to ingest than a lot of broccoli.”