Who Owns the Healthiest Gut Microbiome: Vegans, Vegetarians, or Omnivores?

A balanced diet rich in vegetables is widely recognized as beneficial for overall health, while excessive meat consumption, particularly red meat, can contribute to chronic and cardiovascular diseases. This is partly due to the impact of diet on the gut microbiome. However, eliminating certain foods, such as dairy or animal products, isn't necessarily a universal solution for achieving microbial balance. But can we identify which specific foods influence the gut microbiome? To explore this, a team of researchers analyzed biological samples from 21,561 individuals (vegans, vegetarians, and omnivores) in the United States, United Kingdom, and Italy. Their findings, published in Nature Microbiology, reveal that dietary patterns significantly affect the gut microbiome and the specific microbes linked to better health (1^✔ ✔Trusted Source
Gut microbiome signatures of vegan, vegetarian and omnivore diets and associated health outcomes across 21,561 individuals

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How Diet Shapes the Microbiome and Affects Digestion

The gut microbiome, the set of microorganisms that inhabit our intestine, plays a crucial role in determining a person's health, as it influences many aspects, from digestion to the immune response. So far only few large-scale studies have examined how different diets impact the composition of gut bacteria. This study, which also received European funds, focused in particular on the differences and consequences of different diets on the microbiome. The results show 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.

"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," explains Gloria Fackelmann, first author of the study and researcher at the Cibio Department. The group that conducted this research, which also includes scholars from King's College London, was coordinated by Nicola Segata, professor of Genetics and head of the Computational metagenomics laboratory of the Cibio Department.

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Less Diversity in Vegans and Vegetarians, But Quality Matters More

Based on the results of the analyses, performed at the Metagenomics Laboratory of the Cibio Department, on average vegans have the healthiest diets, followed by vegetarians and omnivores. However, the most interesting data emerged from the study of the diversity of the gut microbiome, that is, by measuring the variety of bacteria that inhabit our intestine. Overall, there was less diversity in vegetarians and vegans than in omnivores, but scientists point out that diversity alone is not a reliable aspect to determine the health of the microbiome, as it does not take into account the quality and functionality of bacteria.

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Bacteria Associated with Meat Digestion in Omnivores

A key aspect of the study was to examine the differences between gut microbiomes. The researchers were able to see how each dietary pattern leads to a unique microbial signature. 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.

Fiber-Fermenting Bacteria in Vegan Microbiomes

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.

Diet Quality Over Pattern

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. Another innovative aspect of the research was the study of how bacteria transfer from food to the microbiome. The scientists 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.

Fiber-Rich, Diverse Diets: Key to a Healthy Microbiome

"We have observed – emphasizes Nicola Segata – 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 research is part of a larger project that aims to identify the benefits of a certain diet based on the specific microbiome of each person or group of people, especially in terms of cardiometabolic health: the so-called precision nutrition.

Reference:

1. Gut microbiome signatures of vegan, vegetarian and omnivore diets and associated health outcomes across 21,561 individuals - (https://www.nature.com/articles/s41564-024-01870-z)

Source-Eurekalert