Friendships often begin with shared interests, hobbies, or experiences, but could our gut microbiomes also play a role? A recent Yale study published in Nature reveals a surprising connection: people within the same social networks share similar gut microbiomes, suggesting our social bonds may influence us at a microbial level.

The microbiome, which consists of bacteria, fungi, and other microorganisms living in the digestive system, has long been studied for its impact on health. This research, however, takes a fresh approach, exploring how our social connections might shape the makeup of these microbial communities.

The study analyzed the gut microbiomes of 1,787 adults across 18 isolated Honduran villages, examining 339,137 microbial strains. Researchers found that people in the same social networks—whether or not they lived together—shared similar microbiomes.

“We found substantial evidence of microbiome sharing happening among people who are not family and who don’t live together, even after accounting for factors like diet, water sources, and medications,” said co-lead author Francesco Beghini. “In fact, microbiome sharing was the strongest predictor of people’s social relationships in the villages we studied, beyond characteristics like wealth, religion, or education.”

Microbial similarities were most pronounced among cohabitants, partners, and household members. However, the study also revealed significant microbial sharing among friends and even second-degree connections, such as a friend’s friend. Shared activities like eating together or physical interactions such as handshakes and hugs likely facilitated this microbial exchange.

Those outside a social network, despite living in the same village, displayed far less similarity in their gut microbiomes.

To confirm these findings, researchers revisited four villages two years later, re-examining the microbiomes of 301 participants. Their results showed that socially connected individuals had grown even more alike in their microbial compositions, reinforcing the idea that social bonds foster microbial similarity over time.

Interestingly, the study also identified specific microbial strains clustered within social groups. These strains were distinct from those found in other groups, indicating that shared social activities contribute to unique microbial communities.

“You have friend groups centred on things like theatre, or crew, or being physics majors,” said co-lead author Jackson Pullman. “Our study indicates that the people composing these groups may be connected in ways we never previously thought, even through their microbiomes.”

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