Soluble fiber renews the cells that form the intestine – 06/30/2023 – Science

A high-fiber diet has been linked to several health benefits, with studies even pointing to protection against diseases such as cancer and diabetes. However, little was known about the interaction between these fibers, the microorganisms present in the intestine and the organ itself.

A study supported by FAPESP and published in the journal Microbiome reveals that a diet rich in a soluble fiber called inulin, found in high concentrations in chicory roots, for example, can even influence the macroscopic characteristics of the intestine, such as its length.

This beneficial action, however, is only possible in the presence of bacteria that digest fiber, providing positive changes in immunity. The results bring new evidence about the importance of fiber in the diet and may help in the understanding of inflammatory bowel diseases.

“In mice that ate a diet with 10% inulin, the intestine was larger than in rodents that consumed only non-soluble fiber [celulose]. When we analyzed this tissue, we saw that the animals on the inulin-rich diet had greater proliferation of stem cells in the epithelium, the layer that separates the contents of the intestine from other organs”, says Renan Oliveira Corrêa, who conducted the investigation with support from FAPESP during his doctorate, at the Institute of Biology at the State University of Campinas (IB-Unicamp).

Part of the analysis was carried out during Corrêa’s internship at the Massachusetts Institute of Technology (MIT), in the United States. The study is part of a project coordinated by Marco Aurélio Ramirez Vinolo, professor at IB-Unicamp and co-author of the recently published article.

Gene expression

By sequencing RNA from the intestinal epithelium of mice, the researchers detected 268 genes expressed differently between groups of animals (diet with and without inulin). The group that ingested the soluble fiber had a greater expression of genes linked to the cell cycle, replication and DNA repair —extremely important in the intestinal epithelium due to the high rate of renewal of the cells that compose it.

On the other hand, genes associated with lipid and fatty acid metabolism showed lower expression in this group of animals that consumed inulin. This modulation is in line with effects already described by other research groups. According to these studies, inulin consumption decreases circulating lipid levels and hepatic steatosis, which is excess fat in the liver.

The inulin-rich diet also increased the expression of genes associated with the differentiation of epithelial cells, an essential process for the organ to grow and replace dead cells. The result is consistent with the increased numbers of mucin-producing cells, which form the mucus that protects the human intestine from the bacteria contained within, and also indicate that the organ is performing its functions well.

“This analysis was carried out with single cell sequencing, perhaps the first carried out entirely in Brazil. This method allows us to know what each cell of the epithelial layer expresses separately”, says Vinolo, who coordinated other works demonstrating the benefits of fiber consumption.

role of bacteria

The bacterial community was drastically modified in animals that ingested inulin. To ensure whether the alterations were important for the effect of this fiber on the epithelium, the researchers carried out experiments with two other groups of mice.

Before receiving inulin, one of the groups took an antibiotic that reduced the intestinal microbiota. The other group, in turn, was made up of animals that did not have any microorganisms living in their bodies. It is a type of mouse known as germ free, which is born in a completely sterile environment and has no contact with anything that could provide microorganisms until the experiment.

Fed with inulin, these animals also did not develop the intestinal phenotype, nor did they have the molecular changes recorded in the group that received soluble fiber, but which had a normal microbiota.

“When they ingested some of the feces [transplante fecal] compared to others that had bacteria in their intestines and consumed inulin, even without ever ingesting the inulin itself, these animals developed the intestinal phenotype, showing the key role of the microbiota in these effects”, explains Corrêa, currently a researcher at the Institut Imagine, in France.

Finally, the study demonstrated that inulin consumption induced greater production of the interleukin-22 molecule (IL-22), a cytokine produced by the immune system and important for gut health. In mice that did not produce IL-22 —because they had the gene coding for this protein silenced—, the inulin-rich diet did not induce the effects observed in other animals.

The same lack of effects was observed in animals that did not express gamma-delta T lymphocytes, a subgroup of T lymphocytes that are located close to the intestinal epithelium, thus revealing an important role played by specific immune cells in this context.

“We observed similar effects with other soluble fibers, such as pectin, contained in fruits. New studies need to be done to understand exactly what each fiber does. But we can say that a balanced diet brings increasingly evident effects that involve a complex interaction between components of the diet, microbiota and cells of our organism”, informs Vinolo.

“Understanding how this works and how we can act on this system is fundamental for us to prevent and even treat inflammatory bowel diseases and others such as diabetes and asthma”, concludes Vinolo.

The article Inulin diet uncovers complex diet-microbiota-immune cell interactions remodeling the gut epithelium can be read here.