The popularity of plant-based diets is on the rise. As such, there is much interest in how eating more plants, and avoiding meat, affects the microbiome. One way to understand these differences is by studying diet-pattern-specific metagenomic profiles across populations. Now, a group from Italy and the United Kingdom analyzed biological samples from 21,561 individuals (vegans, vegetarians, and omnivores) living in the United States, the U.K., and Italy.
The results suggest that the dietary pattern has a strong influence on the gut microbiome and on specific gut microbes that are associated with health. More specifically, “red meat was a strong driver of omnivore microbiomes, with corresponding signature microbes negatively correlated with host cardiometabolic health. Conversely, vegan signature microbes were correlated with favorable cardiometabolic markers and were enriched in omnivores consuming more plant-based foods.”
The study is published in Nature Microbiology in the paper, “Gut microbiome signatures of vegan, vegetarian, and omnivore diets and associated health outcomes across 21,561 individuals.”
“As more and more people adopt vegan and vegetarian diets, we wanted to find out how different their microbiomes are and which microorganisms are responsible for these differences,” explained Gloria Fackelmann, PhD, a postdoctoral fellow at the department of cellular, computational, and integrative biology, University of Trento, in Italy.
Only a few large-scale studies have examined how different diets impact the composition of gut bacteria. This study shows that diet patterns shape the gut microbiome, as they not only determine the microbes necessary for digestion, but also the acquisition of microbes directly from the food itself.
Based on the results of the analyses, there was less diversity in vegetarians and vegans than in omnivores, but diversity alone is not a reliable aspect to determine the health of the microbiome because it does not take into account the quality and functionality of bacteria.
“We have observed,” emphasized Nicola Segata, PhD, full professor and principal investigator at the CIBIO Department of the University of Trento, Italy, and principal investigator at the European Institute of Oncology in Milan, Italy, “that the quantity and diversity of plant-based foods have a very positive impact on the microbiome. Avoiding meat or dairy products does not necessarily have a positive effect if it does not come with a variety of quality plant-based products. From the point of view of the microbiome, what we can generally recommend is that it is important to eat many plant-based foods, especially those rich in fiber. And that food diversity is important.”
The microbiomes of omnivores have an increased presence of bacteria associated with meat digestion, such as Alistipes putredinis, involved in protein fermentation. And omnivores have more bacteria associated with inflammatory bowel disease and an increased risk of colon cancer, such as Ruminococcus torques and Bilophila wadsworthia.
The microbiomes of vegans differ in the number of bacteria involved in fiber fermentation, such as several species in the Bacteroides and Firmicutes phyla, which help produce short-chain fatty acids, such as butyrate. These compounds have beneficial effects on gut health, as they reduce inflammation and maintain a better homeostatic balance with our metabolism and immune system. Finally, the main single difference between vegetarians and vegans is the presence of Streptococcus thermophilus in the microbiome of vegetarians, a bacterium found mainly in dairy products and used in the production of yogurt.
The study highlighted that it is the quality of the diet—rather than the dietary pattern itself —that influences the composition of the microbiome. People with healthier dietary patterns, whether vegan, vegetarian, or omnivorous, showed a more favorable microbiome composition. This suggests that, regardless of the type of diet, eating more plant-based foods and less animal-based foods, especially if highly processed, can be good for gut health.
The scientists also found that vegans had the fewest food-associated bacteria in the microbiome, except for those derived from fruits and vegetables, which were most present. Vegetarians and omnivores, on the other hand, showed a greater number of bacteria linked to dairy products, especially fermented ones.
