We often hear that our gut health depends on what we eat, how stressed we are, or how active our lifestyle is. Yoghurt, fibre, probiotics, and clean eating usually take centre stage in these conversations. But what if your gut bacteria are also shaped by the people you live with?
Think about roommates, partners, siblings, or even family members you share a home with. You share meals, spaces, habits and sometimes even illnesses.
Now, science suggests you may also be sharing something much more personal: the bacteria living inside your gut – and surprisingly, your genes could be influencing theirs too.
A new study has found that gut health is not just a personal matter. It may be a social one.
What This Study Looked At
The study, published on December 18 in Nature Communications, analysed more than 4,000 rats. These rats were genetically unique and lived under carefully controlled conditions.
The researchers divided them into four different groups. Each group lived in a different facility across the United States. Their diets were kept the same, but care routines and environments varied. This setup helped scientists test whether genetic effects on gut bacteria stayed consistent even when surroundings changed.
By studying both the rats' genes and their gut bacteria, researchers discovered something striking. The gut microbiome was shaped not only by an individual rat's genes, but also by the genes of the rats it lived with.
How Genes Can Have Social Effects
Genes themselves do not jump from one body to another. But microbes do.
Some genes help certain gut bacteria grow better. These bacteria can then spread to others through close contact, shared spaces, or grooming. This creates what scientists call “indirect genetic effects”.
"This is not magic, but rather the result of genetic influences spilling over to others through social contact. Genes shape the gut microbiome and we found that it is not just our own genes that matter," says Dr Amelie Baud, a researcher at the Centre for Genomic Regulation in Barcelona and senior author of the study.
In simple terms, your genes can help certain bacteria thrive in your gut. Those bacteria can then move to someone else you live with and affect their gut too.
Three Key Gene–Microbe Links Found
After analysing data from all four rat groups, the researchers identified three strong and consistent gene–microbe connections.
One of the strongest links involved a gene called St6galnac1. This gene adds sugar molecules to the mucus lining of the gut. These sugars act as food for a bacterium called Paraprevotella, helping it grow. This link showed up in all four rat groups, making it especially reliable.
Another genetic region included mucin genes, which help form the protective mucus layer of the gut. These genes were linked to bacteria from the Firmicutes group.
The third region involved the Pip gene, which produces an antibacterial molecule. This gene was linked to bacteria from the Muribaculaceae family, a group commonly found in rodents and also present in humans.
Why Living Together Matters
The large size of the study allowed scientists to measure how much of the gut microbiome was shaped by a rat's own genes and how much came from its cage mates.
They found that some bacteria, especially from the Muribaculaceae family, were influenced by both direct genetic effects and social genetic effects. When these social effects were included in the analysis, the overall genetic influence became four to eight times stronger.
This suggests that genetic influence on gut health may be much bigger than previously thought.
"We've probably only uncovered the tip of the iceberg," says Dr Baud. "These are the bacteria where the signal is strongest, but many more microbes could be affected once we have better microbiome profiling methods."
What This Could Mean for Humans
While this study was done on rats, it raises interesting questions about human health.
People who live together often share gut microbes. If genes influence which microbes grow and those microbes spread socially, then genetic effects on health may go beyond one person.
Genes may not just shape your own disease risk. They could also affect the health of people around you.
The researchers also pointed out a connection between the rat gene St6galnac1 and the human gene ST6GAL1. Earlier human studies have linked ST6GAL1 to Paraprevotella as well. This hints at a shared mechanism across species, where the way our gut mucus is coated with sugars helps decide which microbes survive.
Possible Links to Disease
The study also touches on possible links to diseases, though researchers stress that these ideas are still being explored.
ST6GAL1 has been associated with breakthrough Covid-19 infections in vaccinated people. Paraprevotella has been shown to affect digestive enzymes that the virus uses to enter cells. The researchers believe genetic differences in ST6GAL1 could influence Paraprevotella levels and, in turn, infection risk.
They also suggest a possible connection to IgA nephropathy, a kidney disease. Paraprevotella may change IgA antibodies in the gut. Altered IgA can leak into the bloodstream and damage the kidneys.
These links are still under investigation, but they show how gut bacteria could act as a bridge between genes and disease.
What's Next
The research team plans to take a deeper look at how St6galnac1 affects Paraprevotella and what chain reactions this relationship triggers in the body.
"I am obsessed with this bacterium now. Our results are supported by data from four independent facilities, which means we can do follow-up studies in any new setting. They're also remarkably strong compared with most host-microbiome links. It's a unique opportunity," Dr Baud concludes.
For now, the study offers a new way to think about gut health. It is not just about what you eat or how you live. It may also be about who you live with.
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