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.
Fibre makes the biggest difference. A controlled human study showed that the gut microbiome changes measurably within just a few days when you switch from an animal-based to a plant-based diet, or the other way around. An animal-based diet increased bacteria linked to gut inflammation, whereas a plant-based diet promoted bacteria that break down fibre and are considered protective.
Not everything that is plant-based works equally well. A randomised study (36 participants, 17 weeks) compared a high-fibre diet with a diet rich in fermented foods. Fermented food increased bacterial diversity and lowered inflammatory markers. The high-fibre diet increased the microbiome's capacity to break down fibre, but did not increase diversity. In addition, not everyone responded in the same way: the composition of your current microbiome partly determines how strong the effect is.
A systematic review of nine observational studies found higher levels of Bacteroidetes and Prevotella in vegans than in non-vegans. These bacterial groups are generally considered beneficial. However, because these were comparisons at a single point in time and not an experiment, causality has not been proven here.
The picture is not black and white, however. A cross-sectional study of 89 healthy, normal-weight individuals found no difference in inflammatory markers or gut permeability between vegans, vegetarians, omnivores, and people on a low-carbohydrate diet. This suggests that in people who are already healthy, the direct benefit of a plant-based diet is less clear.
A practical consideration with fully vegan eating: the favourable bacterial composition comes with a documented risk of deficiencies in vitamin B12, iron, and calcium. A well-planned diet or targeted supplementation is therefore necessary.
Claims based on one randomised controlled study (PMID 34256014), one controlled intervention study (PMID 24336217), one systematic review (PMID 34371912), one cross-sectional study (PMID 37828090), and four broad reviews (PMID 25365383, 32098430, 39009882, 30442802). No meta-analyses were used.
Does eating a varied diet help your gut bacteria?
Fermented products have the strongest evidence base for increasing gut bacterial diversity. Eating broadly varied meals also helps, but above all avoid heavily processed products containing emulsifiers such as CMC.
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 eating flaxseed help your gut?
Through its fibre and lignans, flaxseed has a plausible positive effect on the gut, but for the gut as a specific target the evidence in humans is still limited. If you want to take concrete action, opt for at least 30 grams of ground flaxseed per day.
Can you improve your gut bacteria by spending more time in nature?
Whether spending more time in nature improves your gut bacteria is a question the available studies cannot answer; if you want to positively influence your microbiome, diet and body weight have a far better documented effect.
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.
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.