Vegan, vegetarian or omnivore: How diet affects gut health

The fast-emerging gut health trend coincides with our increasing understanding of just how essential the gut is to human health. Gut health can be the key to weight , mental health and can even, some studies suggest, influence the development of autism . But could it also be the key to understanding another key trend - the rise of vegetarian and vegan diets? Plant-based diets are known to be beneficial to the gut. For example, gut microbes help with the fermentation of otherwise indigestible plant polysaccharides, contributing to a healthy, non-inflamed gut barrier. Furthermore, the polyphenols contained by plants can hinder potential pathogens, prevent inflammation, and enhance the gut barrier. Contrasting with this, an animal-rich diet results in increased protein fermentation, potentially leading to inflammation and decreasing the production of short-chain fatty acids. The breakdown of certain animal proteins has been linked to cardiovascular disease. A study published in the journal Nature Microbiology aimed to ascertain how vegan, vegetarian and omnivorous diets changed the composition of the microbiome. The study used a sample of 656 vegans, 1,088 vegetarians and 19,817 omnivores (with self-reported diet patterns), who donated stool samples that underwent shotgun metagenomic sequencing. The microbiomes differed significantly between diets. For example, microorganisms overrepresented in those of omnivores had the role of aiding meat digestion through protein fermentation. However, others are indicators of inflammation and have been linked to inflammatory bowel diseases. In contrast, microorganisms overrepresented in vegan diets were those whose main role was fibre degradation, and produce the short-chain fatty acid butyrate. Streptococcus thermophilus, which is often found in dairy, was significantly more present in vegetarian microbiomes than vegan ones. Dairy consumption marked a major difference between vegetarian and omnivore microbiomes and vegan microbiomes, and was a good predictor of diet all by itself. The microbiomes of vegetarians and vegans were more strongly linked to fruit and vegetables, especially vegetables. Omnivores had greater gut microbial richness than vegans and vegetarians, the study found, although there were no significant difference between vegetarians and vegans. Importantly, some diet patterns select for gut microbes, but sometimes, as in the case of S thermophilus, gut microbes are drawn from food itself. Such food-specific gut bacteria was more common in vegetarians than vegans and omnivores (and more common in omnivores than vegans), although they have a similar number of distinct species to omnivores. This was speculated to be due to the fact that food-specific gut bacteria is more commonly found in dairy, fruits and vegetables than meat, and vegetarians consume dairy as well as fruits and vegetables. Vegan microbiomes contained microbes that are often found in plant and soil microbiomes, which are used in agriculture to promote plant growth. The research suggested that the gut bacteria of vegetarians and vegans are linked to better cardiometabolic health than that of omnivores. Beyond this, the gut bacteria of vegans was more likely to be associated with positive cardiometabolic health than that of vegetarians. However, there were significant positives to the omnivore microbiome. For example, it contained the enzymatic machinery to salvage key nutrients such as vitamin B12, while the vegan one did not. Nevertheless, dietary factors within each diet (such as an omnivore adding a greater amount of fruit and vegetables to their diet) usually transcend the strict dietary pattern followed by a particular person. Sourced From: Nature Microbiology ‘Gut microbiome signatures of vegan, vegetarian and omnivore diets and associated health outcomes across 21,561 individuals’ Published on: 6 January 2025 DOI: 10.1038/s41564-024-01870-z Authors: G Fackelmann, P Manghi, N Carlino et al.