Does fermented food such as yoghurt, kefir and sauerkraut help your gut microbiome?
Fermented foods, and kefir and yoghurt in particular, have the strongest clinical support for a positive effect on the gut microbiome. Feel free to add other fermented products to your diet as well, but be aware that for many of them no good studies in humans yet exist.
Fermented foods such as yoghurt, kefir and sauerkraut have real benefits for your gut microbiome, but the evidence varies considerably from product to product. The strongest signal comes from a randomised trial in healthy adults: people who ate a high-fermented-food diet for 17 weeks subsequently showed greater gut microbiome diversity and lower inflammatory markers in the blood1. The groups were small (18 per group), so this is a promising but not yet definitive finding.
Among the individual products, kefir has the strongest track record. Randomised studies show that kefir helps with lactose intolerance and with the treatment of Helicobacter pylori infection2. Sauerkraut, natto and sourdough bread have far less clinical evidence behind them. For kombucha, miso, kimchi and tempeh, no randomised trials in humans have been conducted at all. That does not mean they do not work, but it also means no firm conclusions can be drawn from them.
Researchers now have a reasonably good understanding of how fermented foods influence the gut microbiome. The live micro-organisms that reach the gut play a role, but so do the biologically active compounds produced during fermentation, such as certain peptides and converted plant substances. Both can influence the composition of your gut bacteria in the short and longer term3.
Regular consumption of fermented products, including fermented dairy, contributes to a more favourable balance in the gut microbiome and supports functions such as protection against infection and immune response4. How large that effect is varies from person to person and from product to product.
There are early indications that fermented foods may also influence the immune system and possibly brain health via the gut microbiome, but the studies are small and have methodological limitations5. In older adults, researchers have investigated whether probiotics and fermented milk help against age-related muscle loss, but the results are mixed and no clear conclusion has emerged6.
Based on PMID 34256014 (randomised trial, n=36), PMID 31387262 (product-by-product review article), PMID 35406140 (mechanism overview), PMID 28914794 (probiotics and dairy), PMID 36102353 (small studies with methodological limitations) and PMID 34523250 (6 clinical studies, mixed results).
Are fermented foods and probiotics good for your gut?
Fermented foods, particularly yoghurt and kefir, show positive indications for gut health; for most other products such as kimchi and kombucha, this has not yet been demonstrated in humans.
Which fermented products have the greatest effect on gut health?
Yoghurt and kefir have the most human evidence supporting a beneficial effect on gut health; for kimchi, kombucha and tempeh, clinical evidence in humans is still entirely absent.
Is fermented food good for your health and your microbiome?
Fermented food, and kefir and yoghurt in particular, likely has beneficial effects on gut flora and several health markers, but the evidence in humans is still limited and does not apply equally to every product.
Can a disrupted gut microbiome weaken your immune system?
A disrupted gut microbiome demonstrably dysregulates your immune system and increases the risk of chronic inflammation. Eating fermented foods is the best-supported way to do something about it.
Can you permanently change your gut microbiome through diet?
Diet does indeed change your gut microbiome, but lasting change requires lasting adjustment of your dietary pattern; a temporary diet has only a temporary effect.
Can your gut microbiome influence inflammation in your body?
Your gut microbiome can influence inflammatory processes throughout your body via the gut wall. Eating more fibre and exercising regularly are the most well-supported ways to influence this favourably.