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.
Fermented dairy products have the strongest support when it comes to gut health in humans. Yoghurt and kefir are the most studied: the micro-organisms in these products survive the acidic conditions in the stomach and demonstrably reach the intestines, where they can favourably influence the microbiome. Kefir also shows signs of benefit for lactose intolerance and for reducing the stomach bacterium Helicobacter pylori, although the clinical evidence for this remains limited.
The strongest human evidence comes from a 17-week randomised trial published in Cell in 2021. Participants who ate a large amount of fermented products (a mix of kefir, yoghurt, kombucha and kimchi) saw their gut microbiome become more diverse and their inflammatory markers in the blood decrease. Notably, a high-fibre diet did not produce this effect. This is currently the most compelling indication that fermented food as a whole has an effect in humans.
Kombucha, miso, kimchi and tempeh have been extensively studied in the laboratory, but for none of these products does a randomised trial in humans exist that measures effects on gut health. Clinical evidence for these products is entirely absent. You can eat them without concern, but a proven benefit for your gut has not yet been demonstrated.
An analysis of 19 human intervention studies shows that fermented food can alter the composition of the gut microbiome, but outcomes vary considerably between studies. Whether those microbiome changes actually lead to better health has not yet been firmly established. Larger and longer-term studies are still lacking.
Anyone who wants to do something concrete for their gut is best off starting with yoghurt or kefir: these are the products with the most human studies behind them. Choose products with live cultures where possible. Other fermented products such as kimchi and tempeh can be a valuable addition to your diet, but the claim that they specifically benefit your gut has not yet been demonstrated in humans.
All claims are based on reviews (PMID 38081933, 35406140, 31387262, 32232406, 30452699, 32512787, 39888432) and one randomised controlled trial (PMID 34256014). No meta-analyses are available in this source set.
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.
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.
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.
Are plant-based diets better for your gut than mixed diets?
A plant-based diet appears to be beneficial for your gut bacteria, but fermented foods perform at least as well in a direct comparison. Whether healthy people also notice a meaningful long-term benefit has not yet been demonstrated.
Does green tea help your gut health?
Green tea extract showed measurable improvements in gut wall integrity and gut inflammation in a randomised trial; the signals are encouraging for a healthy gut, but it is too early to make recommendations for serious gut conditions.
Does intermittent fasting help your gut health?
For healthy people and people with metabolic syndrome there is reasonably consistent evidence that intermittent fasting has a beneficial effect on gut bacteria and inflammation markers. If you have a chronic bowel disease, discuss fasting with your doctor first, as evidence in that group is still lacking.