Researchers at Stanford randomly assigned healthy adults to either a high-fiber diet or a diet rich in fermented foods like yogurt, kimchi and kombucha for ten weeks, then tracked both groups' gut bacteria and immune markers in detail.
The high-fiber group's microbiome diversity held steady despite eating more plants, and only some of them saw their inflammation markers shift. The fermented-food group's gut microbiome diversity rose steadily, and the levels of inflammatory signaling proteins in their blood fell across the group as a whole.
The fiber result surprised the researchers, who expected it to broadly reduce inflammation; instead it appeared to depend on each person's starting microbiome. The study ran 17 weeks total with 18 people per diet arm, a small, short trial in healthy adults, not people with existing disease, and its primary immune measure did not change in either group, so the inflammation drop is a signal, not proof.
Read the original study
Wastyk et al., Cell, 2021 · doi.org/10.1016/j.cell.2021.06.019
Fermented food moved more markers than fiber.
Source
- Wastyk, H. C., Fragiadakis, G. K., Perelman, D., Dahan, D., Merrill, B. D., Yu, F. B., Topf, M., Gonzalez, C. G., Van Treuren, W., Han, S., Robinson, J. L., Elias, J. E., Sonnenburg, E. D., Gardner, C. D., & Sonnenburg, J. L. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137–4153.e14. https://doi.org/10.1016/j.cell.2021.06.019