Gut

Eating plants gives the gut a healthier set of bacteria

By WhyStopHarmingAnimals.com

What we eat decides which bacteria live in our gut, and the bacteria that thrive on plants are linked with better health than the ones that thrive on meat[1]. The largest study so far, covering 21,561 people, found that vegans, vegetarians and omnivores each carry a distinct microbial signature[1], with red meat as the strongest driver of the omnivore one[1].

Three diets, three signatures

The 2025 study in Nature Microbiology compared the gut bacteria of vegans, vegetarians and omnivores[1]. Each group had its own recognisable signature[1]. Red meat did more than any other food to shape the omnivore profile, and the microbes in that profile tracked with worse cardiometabolic health[1]. The microbes in the vegan signature tracked with better markers[1].

Those vegan-signature microbes also turned up in omnivores who ate more plants[1]. The bacteria respond to the food on the plate, whatever label the person eating it uses[1]. The study is observational, so it shows which microbes go with which diets and which health markers, without proving that the microbes cause the difference.

What fibre does

Reviews of the microbiome research describe how the shift happens[2]. A 2019 review in Frontiers in Nutrition found plant-based eating comes with a more diverse and more stable microbiome[2]. Fibre raises lactic-acid bacteria, Roseburia and E. rectale, and lowers Clostridium and Enterococcus[2].

A 2020 review in Medicina found that well-planned vegan diets change both the mix of bacteria and the chemistry they carry out, with fibre, polyphenols and antioxidant vitamins doing the work[3]. The same review lists the nutrients a vegan diet has to plan for, which is the “well-planned” part[3].

A 2014 review in Nutrients described the vegan gut as unusual on two counts: it carries fewer of the bacteria that turn harmful and more of the protective species[4]. The authors argue that lower inflammation is what links that bacterial profile to the health advantages seen in vegans[4].

Crohn’s disease stayed in remission

Crohn’s disease is an inflammatory bowel disease that tends to relapse. In a study published in the World Journal of Gastroenterology in 2010, 22 adults whose Crohn’s was already in remission were asked to keep eating a plant-based diet for two years[5]. Of the 16 who did, 15 (94%) were still in remission at the end[5]. Of the six who went back to eating animals, two (33%) were[5].

The study was small, ran at a single hospital and was not randomized[5], so the people who stuck with the diet may have differed in other ways from those who didn’t. The gap between the two groups is still wide[5].

Reviews of inflammatory bowel disease point the same way[6][7]. A 2019 review in Translational Pediatrics, covering children and adults, recommends plant-based diets for the condition without reservation and names diets high in animal fat and low in fruit and vegetables as the pattern most often tied to higher risk[6]. A 2020 review in Expert Review of Gastroenterology & Hepatology found that a westernized diet tracks with both the risk of inflammatory bowel disease and relapse, and that a plant-based diet may help by lowering inflammation and restoring a balanced gut[7]. Its authors say plainly that better-quality studies are still needed[7].