Can eating more fermented foods change your gut microbiome?

What does the research say?

In a small Stanford study, adults who gradually increased fermented foods — yoghurt, kefir, kimchi, kombucha and fermented vegetables — to around six servings a day saw the variety of their gut bacteria increase, and several blood markers of inflammation fall. A comparison group who increased fibre instead didn’t see the same change in diversity over the study period.

The science

Participants were randomised to a high-fermented-food or a high-fibre diet for a 10-week intervention, with a ramp-up and follow-up period either side. The researchers measured gut microbiota composition from stool samples and profiled immune markers in blood.

In the fermented-food group, microbiota diversity rose steadily across the intervention and 19 inflammatory proteins decreased, including interleukin-6. In the high-fibre group, diversity stayed broadly stable, and immune responses varied between individuals — the authors suggest the starting microbiome may influence how someone responds to extra fibre.

Key findings

Microbiota diversity increased with fermented food intake, in a dose-related way.
19 inflammatory markers decreased in the fermented-food group, including IL-6.
The high-fibre group did not show the same increase in diversity during the study window.
Responses to the high-fibre diet varied between participants.

Limitations

Small sample (36 people) of healthy adults — results may not apply to people with digestive conditions.
Diets weren’t blinded; participants knew what they were eating.
Inflammatory markers and microbial diversity are measurements, not health outcomes such as disease rates.
Six servings a day is a lot — the practical dose for most people is unknown.

References

Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137–4153. doi.org/10.1016/j.cell.2021.06.019