A new study reveals that close social relationships can drive the transfer of gut microbes, independent of shared surroundings.
Living with friends or family may subtly influence your gut bacteria, according to a new study from the University of East Anglia.
Research on a population of small island birds found that individuals share more of their gut microbes with those they interact with most often. Scientists say this pattern likely applies to humans as well.
Earlier studies have suggested that spouses and long-term cohabitants tend to have more similar gut microbiomes than unrelated individuals, even when their diets differ. This new research provides clearer evidence that close social contact itself, rather than just a shared environment, helps drive the exchange of gut bacteria.
How the research happened
The team studied the Seychelles warbler, a small songbird that lives on Cousin Island in the Seychelles. Researchers collected fecal samples to analyze the birds’ gut microbiomes, which are communities of beneficial bacteria in the digestive system.
Dr. Chuen Zhang Lee, from UEA’s School of Biological Sciences, conducted the study as part of his PhD. He said: “To uncover how gut bacteria spreads between social partners, we meticulously collected the birds’ poo over several years. We gathered hundreds of samples from birds with known social roles – breeding pairs, helpers, and non-helpers living in the same group, and in different groups.”
He added, “This allowed us to compare the gut bacteria of birds that interacted closely at the nest versus those that did not. We studied their anaerobic gut bacteria, which thrive without oxygen. And it gave us a rare insight into how social bonds can drive the transmission of gut microbes.”
A natural laboratory in the Indian Ocean
Senior researcher Prof David S Richardson explained why the location was ideal for the study. “Cousin Island is small, isolated, and the warblers never leave it. That means every bird on the island can be individually marked and followed throughout its life. This offers scientists an exceptional opportunity to study life-long biological processes in the wild.”
Each bird is fitted with colored leg rings, allowing researchers to track behavior, health, and genetics over many years. This creates conditions similar to a controlled population while preserving a natural environment.
“It gives us the best of both worlds,” said Prof Richardson. “We can study animals living natural lives, with natural diets and gut bacteria, while still being able to collect detailed data from known individuals.”
Sharing gut microbiota with friends
The findings show a clear link between social behavior and microbial similarity. “We found that the more social you are with another individual, the more you share similar anaerobic gut bacteria,” said Dr. Lee.
“Birds who spent a lot of time together at the nest – breeding couples and their devoted helpers – shared a lot of this type of gut bacteria, which can only spread through direct, close contact.”
He explained that these microbes cannot survive outside the body. “These anaerobic microbes can’t survive in the open air, so they don’t drift around in the environment. Instead, they move between individuals through intimate interactions and shared nests.”
How home life shapes our microbiomes
The researchers say the results may reflect what happens in human households. “Whether you’re living with a partner, housemate, or family, your daily interactions – from hugging, kissing, and sharing food prep spaces – may encourage the exchange of gut microbes,” said Dr. Lee.
“Anaerobic bacteria are some of the most important for digestion, immunity, and overall health. Once inside the gut, they thrive in oxygen‑free conditions and often form stable, long‑term colonies.”
He adds, “That means the people you live with might subtly shape the microscopic ecosystem inside you. Translated into human terms, this means that cozy nights in, shared washing‑up duties, and even sitting close on the sofa may bring your microbiomes quietly closer together.”
“Sharing beneficial anaerobic bacteria could strengthen immunity and improve digestive health across a household,” he concluded.
Reference: “Social Structure and Interactions Differentially Shape Aerotolerant and Anaerobic Gut Microbiomes in a Cooperative Breeding Species” by Chuen Zhang Lee, Sarah F. Worsley, Terry Burke, Jan Komdeur, Falk Hildebrand, Hannah L. Dugdale and David S. Richardson, 10 April 2026, Molecular Ecology.
DOI: 10.1111/mec.70304
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