Close Interactions with Roommates or Family May Reshape Each Other's Gut Microbiome
A recent study shows that close social relationships can drive the transmission of gut microbes between individuals, an effect independent of sharing a living environment. In other words, your close interactions with roommates, partners, or family members may be quietly reshaping each other's gut microbiome.
A team from the University of East Anglia discovered in a group of birds living on a small island that individuals who interacted more frequently had more similar gut microbiome compositions. Scientists believe this phenomenon likely applies to human societies as well. Previous research has suggested that spouses or long-term cohabitants often have more similar gut microbiomes than unrelated individuals, even if their diets are not identical. The new study provides further evidence that intimate social contact itself, not just the environmental factor of "living together," plays a key role in promoting gut bacteria exchange.
The study subjects were Seychelles warblers, a small songbird inhabiting Cousin Island in the Seychelles. The research team collected fecal samples from these birds and analyzed their gut microbiomes – the communities of beneficial bacteria living in the digestive system. Dr. Chuen Zhang Lee, first author of the paper and from the School of Biological Sciences at the University of East Anglia, explained that to track how gut bacteria spread between social partners, the team systematically collected bird fecal samples over several years and established a social role profile for each bird: including breeding partners, "helpers" who assisted in caring for chicks in the nest, and individuals who did not take on assisting roles in the same or different groups.
This design allowed researchers to compare the gut microbiomes of individuals with close interactions in the nest with those who had less contact with each other. The team focused on analyzing anaerobic gut bacteria – bacteria that thrive in oxygen-deprived environments and are intolerant of oxygen. Dr. Lee pointed out that this specific microbial group provides a rare perspective on understanding how social bonds drive gut microbiome transmission.
The choice of Cousin Island as a "natural laboratory" was not accidental. Senior researcher Professor David S. Richardson explained that Cousin Island is small and relatively isolated, and Seychelles warblers do not leave the island. This means that every bird on the island can be individually marked and tracked long-term from its lifetime perspective. Each bird wears a colored leg band, allowing researchers to accurately identify individuals in the wild and record their behavior, health status, and genetic information over time. This system provided scientists with near-"controlled population" research conditions while maintaining the natural ecological environment, natural diet, and natural gut microbiome.
The results showed a clear correlation between an individual's social behavior and the similarity of their gut microbiome. Dr. Lee stated that the more frequently an individual interacted with another, the more anaerobic gut bacteria they shared. Breeding pairs and dedicated "helpers" who spent a lot of time together in the nest had highly similar compositions of these anaerobic bacteria, and these microbes can only be transmitted through direct, close contact. He added that these anaerobic bacteria cannot survive outside the body and cannot float freely in the air, so they are not simply spread through environmental diffusion. Instead, they are transferred between individuals during intimate interactions, shared nests, and living spaces.
Researchers point out that this pattern is likely to exist in human families and shared housing as well. For humans, whether living with a partner, roommate, or family member, daily physical contact, hugs, kisses, or even sharing kitchen countertops, utensils, and other living spaces can promote the exchange of gut microbes. Anaerobic bacteria play a key role in digestion, immunity, and overall health, and once successfully colonized in the gut, they can often exist stably in anaerobic environments for a long time. Researchers emphasize that this means the people you spend time with may be unknowingly shaping your internal "micro-ecosystem."
If this bird study is analogized to human life scenarios, then the cozy nights spent at home, the daily chores of washing dishes together, or even just squeezing onto the sofa to watch TV can quietly bring each other's gut microbiomes "closer." Researchers speculate that in family or shared living environments, sharing beneficial anaerobic bacteria may, to some extent, enhance the immunity and improve the digestive health of all family or group members.
The related research results, titled "Social Structure and Interactions Differentially Shape Aerotolerant and Anaerobic Gut Microbiomes in a Cooperative Breeding Species," were published in the journal *Molecular Ecology* in April 2026.