What you eat not only affects your waistline but it also affects the trillions of bacteria living in your stomach. A new study examining more than 21,000 people from the US, UK and Italy has shed light on how different diets – omnivores, vegetarians and vegans – affect gut health.

This large-scale research explored the unique bacterial communities associated with each dietary pattern and their relationship to overall health.

Meat based diets and their effects

The researchers found that people who ate meat (omnivores) had higher levels of specific gut bacteria like Ruminococcus torx and Bilophila wadsworthia. These microbes are also linked to health risks associated with digesting red meat, such as inflammatory bowel disease (IBD) and colon cancer.

The breakdown of certain animal proteins produces a compound called TMA, which is further processed in the liver into TMAO, a substance linked to heart and vascular diseases. However, it was most commonly seen in people who ate high amounts of red or processed meat.

Plant-Based Diet: Boost Gut Health

On the other hand, vegetarians – those who completely avoid animal products – showed a different microbial profile. Their gut bacteria were associated with better cardiometabolic health (heart and metabolic health).

Microorganisms that thrive on a plant-based diet promote the production of short-chain fatty acids (SCFAs), which support a healthy gut lining, reduce inflammation and strengthen the immune system.

Vegetarians – those who abstain from meat but consume dairy and eggs – fall somewhere between omnivores and vegans. Dairy consumption was linked to specific bacteria such as Streptococcus thermophilus, which are often found in yogurt and cheese.

Diet and gut health: a two-way street

Plants are food not only for humans but also for the bacteria in our gut. Rich in fiber and polyphenols (plant chemicals with health benefits), they nourish the bacteria that maintain gut health.

Conversely, diets high in animal protein can cause harmful fermentation, resulting in inflammation and “leaky gut” – a condition where the gut barrier becomes less effective.

Unlike previous studies limited by small sample sizes or single-country data, this research included diverse populations and included thousands of participants.

This highlights the potential for tailored nutritional interventions to improve health by focusing on gut bacteria.

The study was partially funded by ZOE Ltd., a personal nutrition company, and some of the researchers involved have ties to the company.

The findings suggest that eating more plant-based foods, even for meat eaters, can improve gut health. While diet is only one piece of the puzzle, this research underscores its importance in shaping the microbiome and, by extension, overall health.