According to the evidence currently available to us, 70% of our immune system resides in the intestine. There, its cells interact with the complex community that inhabits us: a lot of different microorganisms that together are called the intestinal microbiota and that perform very important functions for the proper functioning of our body.

Taking this into account, it is not surprising that the health of the microbiota is essential for our well-being and, more specifically, for that of our immune system. In this line, a new study carried out on mice has found that the sugar present in our diet it severely damages our microbiome and, consequently, also our immune system.

bacterial imbalances

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As explained by the authors of this work in the article published on the subject in the scientific journal Cell, This phenomenon is directly related to the competition that exists between the different species that are part of the microbiota. Normally, this competition leads to a complex balance that is beneficial to us. However, it seems that the excessive sugar intake promotes the growth of certain species (notably, Faecalibaculum rodentium in mice) that eliminate segmented filamentous bacteria, which we might consider ‘good’ bacteria (again, in mice).

In turn, this imbalance (called dysbiosis) leads to a reduction in a specific type of immune cell called Th17 lymphocytewhich in the case of mice protects them against diseases such as obesity induced by a high-fat diet.

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This happens because high doses of sugar damage the inner lining of the intestine, triggering inflammation that inhibits the growth of segmented filamentous bacteria and allows them to be displaced by other species such as F. rodentium.

An experiment on mice

To reach these conclusions, the authors of the work took five-week-old male mice and colonized part of them with segmented filamentous bacteria. Subsequently, they were fed a diet high in fats and sugarssimilar to the western diet.

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After only 4 weeks, the segmented filamentous bacteria in the mice had been replaced by F. rodentium, Th7 lymphocytes had greatly decreased in population and the mice had gained weight and developed glucose intolerance and insulin resistance.

Altering any of these factorsHowever, the results varied substantially. For example, mice that had been colonized with segmented filamentous bacteria but fed a diet that was only high in fat (not sugar) retained Th17 cells; and if instead they were fed the Western diet but not colonized with segmented filamentous bacteria, they gained weight and developed diabetes.

Questions still to be answered

The main novelty presented by this work is that it illuminates a mechanism that directly connects sugar intake with effects on the immune system. However, there are still some unknowns to answer.

For example, segmented filamentous cells are not found naturally in the human digestive tractso the replicability of these results in humans is one of them.

In addition, the research does not take into account other factors that could decisively influence the final result, such as the role of physical activity and exercise.

Still, there are reasons to think that sugar may have a similar effect on the human microbiota: many previous studies have shown that adults with metabolic syndrome show a lack of bacteria that induce the appearance of Th17 cells, in favor of other strains.

References

Yoshinaga Kawano, Madeline Edwards, Yiming Huang, Angelina M. Bilate, Leandro P. Araujo, Takeshi Tanoue, Koji Atarashi, Mark S. Ladinsky, Steven L. Reiner, Harris H. Wang, Daniel Mucida, Kenya Honda, Ivaylo I. Ivanov . Microbiota imbalance induced by dietary sugar disrupts immune-mediated protection from metabolic syndrome. Cell (2022). DOI: https://doi.org/10.1016/j.cell.2022.08.005