How close friends may be changing your gut bacteria – Earth.com

You spend time with friends, share meals with family, and sit close to people you care about. These moments feel simple, but something deeper may be happening. Your body may be changing with every interaction.
Scientists from the University of East Anglia found that social life can shape the bacteria living in your gut. This discovery adds a new layer to how we understand health and relationships.
The gut is full of bacteria. These are not harmful in most cases. Many of them help your body work better. They break down food, support your immune system, and keep the body balanced.
This group of bacteria is called the gut microbiome. Each person has a unique mix. Food and environment affect it, but now scientists see that social interaction also plays a role.
So your gut is not just shaped by what you eat. It is also shaped by who you spend time with.
To understand this idea, researchers studied the Seychelles warbler. This small bird lives on a tiny island and rarely leaves it. That makes it perfect for long-term study.
Scientists can track every bird, observe behavior, and study relationships over time. This gives a clear picture of how social life affects biology.
“To uncover how gut bacteria spreads between social partners, we meticulously collected the birds’ poo over several years,” said Dr. Chuen Zhang Lee.
“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.”
This allowed us the team to compare the gut bacteria of birds that interacted closely at the nest versus those that did not, noted Dr. Lee.
The researchers focused on anaerobic gut bacteria, which grow without oxygen, and this helped them understand how close social interactions can spread these microbes between individuals.
The results showed a clear pattern. Birds that lived together had more similar gut bacteria than those living apart.
This shows that shared space matters. But the study goes further. It shows that interaction matters even more.
Birds that spent more time together had gut bacteria that looked more alike. This means daily contact allows bacteria to pass between individuals.
Not all bacteria behave the same way. Some can survive outside the body. Others cannot.
Anaerobic bacteria cannot survive in oxygen. They need close contact to move from one body to another.
Birds that worked closely together, especially at the nest, shared more of these bacteria. These birds fed chicks, stayed near each other, and interacted often.
“We found that the more social you are with another individual, the more you share similar anaerobic gut bacteria,” Dr. Lee said.
This shows that closeness, not just proximity, drives this sharing.
Within bird groups, some individuals act as helpers. These helpers assist in raising young birds. This role keeps them in constant contact with others.
Because of this, helpers share more gut bacteria with the group. Their microbiome becomes more similar to those around them.
This shows that behavior and responsibility within a group can influence biology.
Sharing a home, cooking together, or even sitting close creates chances for bacteria to move between people.
“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,” explained Dr. Lee.
These small actions happen every day. Over time, they may shape your gut microbiome.
The idea of sharing bacteria may sound strange at first, but not all bacteria are harmful. In fact, many of them help the body function better.
Some aid in digestion, while others protect against disease and keep the body balanced. Because of this, sharing beneficial bacteria may even support better health within a household.
This research shows that human connection goes beyond emotions. It also affects the body in hidden ways.
The people around you may influence your health at a level you cannot see. Your daily habits, your closeness, and your relationships all play a role.
So the next time you share a meal or sit close to someone, remember this. Your connection may be shaping more than just your day.
The study is published in the journal Molecular Ecology.
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