Marcella La Cioppa Vegan, vegetarian and omnivorous diets influence intestinal microorganisms, but excluding certain foods can have both favorable and unfavorable complex effects on overall well-being. The confirmation comes from an international study coordinated by the Cibio Department.
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A diet rich in a variety of plant-based foods is generally well-accepted for being healthful. At the same time, excessive consumption of meat-in particular, red meat-has been associated with higher morbidity and cardiovascular events. This is mainly due to the influence of nutrition on the gut microbiome.
At the same time, avoiding certain foods, like dairy or other animal products, is not a solution that would work for everyone in maintaining a balanced internal microbiome.
But can we identify specific foods that drive differences in the gut microbiome? To begin to answer this question, a research team analyzed biological samples from 21,561 participants including vegans, vegetarians, and omnivores across the United States, the United Kingdom, and Italy. Their results showed that diet strongly affected the gut microbiome and specific microbes associated with improved health.
The study
The gut microbiome, consisting of trillions of microorganisms inhabiting the intestines, is crucial in determining an individual’s health, from digestion to immune responses. Until recently, large-scale studies on how different diets affect gut bacterial composition have been limited.
The European-funded study explored how such dietary regimes vary and their effect on the microbiome. It had proven that diet molds the gut microbiome not just by selecting for microbes providing nutritional benefits, but also by introducing microbes directly coming from the food.
According to Gloria Fackelmann, a researcher at the Cibio Department, first author of the study:
“As diets become increasingly vegan and vegetarian, we wanted to understand how different their microbiomes can be and which microorganisms are responsible for these differences.”
The research team, including scientists at King’s College London, was headed by Nicola Segata, professor of genetics and head of the computational metagenomics laboratory at the Cibio Department.
Analyses done in the Metagenomics Laboratory at Cibio established that, on average, vegan diets were the healthiest, followed by vegetarian and omnivorous diets. However, the most interesting data concerned gut microbiome diversity-a measure of the variety of bacteria in the intestines.
Even though vegetarians and vegans have less microbial diversity than omnivores, researchers have pointed out that diversity alone is not really a good marker of microbiome health since diversity does not reflect the quality or function of bacteria present.
Among the key things the study explored were gut microbiomes. The findings gave evidence that each type of diet yields a special microbial “signature.” Omnivores had a higher abundance of bacteria associated with the digestion of meat in their gut microbiomes, including Alistipes putredinis, which plays a role in protein fermentation. But they also had more “negative” bacteria, including Ruminococcus torques and Bilophila wadsworthia, linked to inflammatory bowel diseases and an increased risk of colon cancer.
In contrast, vegans’ microbiomes had more bacteria involved in fiber fermentation, such as Bacteroides and Firmicutes, which help produce short-chain fatty acids like butyrate. These compounds provide considerable health benefits, including reducing inflammation and maintaining metabolic and immune system balance. The main difference in vegetarians compared with vegans was the presence of Streptococcus thermophilus, a bacterium commonly found in dairy products and used in yogurt production.
Diet quality and microbiome health
The study emphasized that diet quality—more than the dietary model itself—influences microbiome composition. People with healthier diets, whether vegan, vegetarian, or omnivorous, exhibited a more favorable microbiome composition. This suggests that regardless of diet type, incorporating more plant-based foods and reducing processed animal-based products can promote optimal gut health.
Another novelty of this research was the bacterial transfer from food to the microbiome. Indeed, scientists detected that vegans have the lowest number of food-associated bacteria in their microbiome-except for those from fruits and vegetables-which are way more abundant. On the other side, vegetarians and omnivores showed a greater abundance of bacteria associated with dairy products, mostly fermented ones.
Nicola Segata said:
“What we saw was that variety and quantity of plant-based food items greatly influence the microbiome very positively. Just avoiding meat or dairy products does not create a positive effect unless accompanied by diversity and quality in plant-based foods. General advice from the perspective of a microbiome would be to eat a wide variety of plant-based foods, high in fiber in particular. Variety in food is very important.
It represents part of a larger research effort, which has tried to determine specific dietary patterns that may lead to individual or group-specific microbiomes associated with benefits for cardiometabolic health. One approach, sometimes referred to as precision nutrition, is dietary recommendations that are specific to the unique microbiome profile.
Source: Nature Microbiology
