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High-fiber diet

High-fiber diet keeps gut microbes from eating the colons lining, protects against infection, animal study shows.

Nutritionexplorations - Animal Study

When microbes inside the digestive system don't get the natural fiber they rely on from food, they begin to munch on the natural layers of mucus that lines a gut. This can get to the point were dangerous invading bacteria can affect the colon wall. New research in mice has shown this. When mice are raised germ-free, then given a transplant of human gut microbes, the impact of fiber on their colons can be seen. Mice that are fed a high-fiber diet maintained a thick mucus layer along the lighting of their colons, while those it received a fiber free diet saw the mucus layer growth center as bacteria capable of digesting mucus, proliferated. The thin layer allowed a pathogen bacteria access to the cells of the colon wall.

This sounds like a plot from a 1950s science fiction movie but helpful bacteria do begin to eat their host from within if they don't get what they want. New research has shown that this is what happens when microbes inside the digestive system don't get the natural fiber they rely on. Starve they begin to munch on the mucus aligns the gut and eroded to the point were dangerous bacteria can infect the colon wall.

An international team of researchers shows the impact of fiber deprivation on the gut of especially raised mice. The mice were born and raised with no gut microbes of their own, then received a transplant of 14 bacteria that grow in the human gut. Scientists know the full genetic signature of each one, making it possible to track their activity over time.

The findings have implications for understanding not only the role of fiber but also the potential of using fiber to counter the effects of digestive tract disorders. The lesson we are 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. Using the University of Michigan's special gnotobiotic, or germ-free, mouse facility and advance genetic techniques that allow them to determine which bacteria were present and active under different conditions. They studied the impact of diets with and without fiber content. They also infected some of the mice with a bacterial strain that does to mice with certain strains of Escherichia coli can do to humans. These can cause gut infections that lead to irritation, inflammation, diarrhea and more. The result: the mucus layer stayed thick and the infection didn't take full hold, in mice that received a diet that was 15% fiber from minimally processed grains and plants. But when the researcher substituted diet with no fiber and it, even for a few days, some of the microbes in their guts begin to munch on the mucus.

They also tried a diet that was rich in prebiotic fiber, purified forms of soluble fiber similar to what some processed foods and supplements currently contain. This diet resulted in the same erosion of the mucus layer. Researchers also saw that the mix of bacteria change depending on what the mice are being fed day by day. Some species of bacteria in the transplanted micro biome were more common, meaning they have reproduced more. And the four bacteria strains of flourish most in low fiber and no fiber conditions were the only ones that make enzymes that are capable of breaking down the long molecules called glycoproteins that make up the mucous layer.

In addition to looking at the bacteria based on genetic information, researchers can see which fiber digestive enzymes the bacteria were making. They detected more than 1600 different enzymes capable of degrading carbohydrates, similar to the normal human gut.

Just like the mix of bacteria, the mix of enzymes change depending on what the mice are being fed. Images of the mucous layer and the goblet cells of the colon wall that produce the mucus constantly showed the layer was thinner the less fiber the mice received. While mucus is constantly being produced and integrated in a normal gut, the change in bacteria activity under the lowest fiber conditions meant that the pace of eating was faster than the pace of production, almost like an overzealous harvesting of trees outpacing the planting of new ones.

When the researchers infected the mice with Citrobacter rodentium, the E. coli like bacteria that they had observed, these dangerous bacteria flourished more in the guts of mice fed in a fiber free diet many of those mice began to show signs of illness and lost weight. When the scientist looked to samples of their gut tissue. they saw not only a much thinner mucus layer they also saw inflammation across a wide area. Mice received a fiber rich diet before being infected had some inflammation but across a much smaller area.

Thanks to the gnotobiotic facility, having all the resources here was key to making this project work and the lab allowed us to pull it all together. Going forward the researchers intend to look at the impact of different prebiotic fiber mixes, and of diets with more intermittent natural fiber content over a longer period. They also want to look for biomarkers that could tell them about the status of the mucus layer in human guts for example, as the abundance of mucus digesting bacteria strains and what is the effect of low fiber on chronic disease such as inflammatory bowel disease. Even though this work was done on mice the take-home message for humans is that eating fiber from diverse natural sources directly influences your microbiota and from there it may influence the status of your guts mucus layer and tendency toward disease. It is still the question of whether we can cure cultural lack of fiber with something more purified and easy to ingest than a lot of broccoli.