How your housemates could be changing your gut bacteria

It’s not just milk, bills and a pile of dishes; You probably share gut bacteria with your roommates, too.

That’s according to scientists from the University of East Anglia (UEA), who found that living with friends or partner quietly changes your gut bacteria.

“Whether you live with your partner, flatmate or family, your daily interactions, such as hugging, kissing and sharing food preparation areas, can encourage the exchange of gut microbes,” said Dr Chuen Zhang Lee from UEA’s School of Biological Sciences.

Researchers studied a colony of small island birds and found that they shared more of their gut bacteria with the birds they spent the most time with, and the same principle is thought to apply to humans.

From birth, the gut microbiome, composed of bacteria, viruses and fungi, is shaped by our environment, initially from our mother and later by our social interactions.

Previous studies in humans have hinted that who we live with has a big impact on the microbes we have, even when we eat different diets. Experts have suggested that partners share about 30 percent of the gut-resident microbes alone.

But new bird research provides unusually clear evidence of how social proximity, not just shared environment, drives gut bacterial exchange.

For the study published in the journal Molecular EcologyThe researchers collected data on the Seychelles warbler, a small songbird found on Cousin Island, by collecting fecal samples from breeding pairs and other birds living in the group over several years.

These samples were used to analyze the birds’ gut microbiomes, the diverse communities of “good” bacteria living in their digestive tracts.

“This allowed us to compare the gut bacteria of birds that interacted closely in the nest with those that did not interact closely in the nest,” Dr Lee said. “We studied anaerobic gut bacteria that thrive in the absence of oxygen, giving us a rare insight into how social bonds can drive the transmission of gut microbes.”

Because the birds never leave the island, scientists were able to track them throughout their lives and how close they were to other birds by wearing colored leg rings.

“We found that the more social you are with another person, the more you share similar anaerobic gut bacteria,” Dr Lee said.

“Birds that spent a lot of time together in the nest (breeding pairs and their faithful helpers) shared many of these types of gut bacteria, which can only be spread through direct, close contact.

“These anaerobic microbes cannot survive outdoors, so they do not circulate in the environment. Instead, they move between individuals through close interactions and communal nests.”

Researchers say something similar can happen in human homes, whether with roommates or spouses. However, it may improve immunity and digestive health.

“Anaerobic bacteria are some of the most important bacteria for digestion, immunity and general health,” Dr Lee said.

“Once in the intestines, they thrive in anoxic conditions and often form stable, long-term colonies. This means the people you live with can expertly shape the microscopic ecosystem inside you.”

“Translated into human terms, this means that cozy nights at home, sharing dishwashing chores, and even sitting close together on the couch can quietly bring your microbiomes closer together.

“Sharing beneficial anaerobic bacteria can boost immunity and improve digestive health throughout the home.”