December 18, 2024, 3:15 pm | Read time: 5 minutes
According to researchers at Yale University, our social contacts influence us more than we think. Friends and acquaintances can apparently change our gut microbiome – in other words, the entirety of the bacteria living in our gut. And this is not without consequences. FITBOOK editor Sophie Brünke presents the results of the study.
Since the non-fiction book Gut: The Inside Story of Our Body’s Most Underrated Organ became a bestseller, it’s become widely recognized that the gut and its resident bacteria significantly influence our health. Moreover, our dietary habits and environment substantially shape the composition of this bacterial community, technically referred to as the microbiome. However, have you ever considered that friends might also play a role in enhancing or diminishing our gut health?
Overview
Researchers Studied 18 Villages in Honduras
Friendship does not end with the same hobbies and preferences but extends to a shared intestinal flora. These are the findings of a study by Nicholas Christakis, Professor of Social and Natural Sciences, and his team. Their research focused on the relationship between the structure of people’s social networks and the composition of their gut microbiome.1
For the study, the researchers mapped the social networks of around 1800 adults who lived in 18 isolated villages in Honduras and were part of a larger cohort study. Using a questionnaire, the scientists mapped the social networks within each village. In total, there were the following relationships:
- 410 (spouses) partners
- 303 fathers
- 594 mothers
- 1059 siblings
- 427 children
- 1627 close friends
- 1749 people with whom free time is spent
- 1902 personal or private conversations
Some of these relationships naturally overlapped. The researchers ultimately identified 4658 unique social relationships.
They also had detailed data on the composition of each participant’s individual microbiome. This included 2543 microbial species and 339,137 different bacterial strains. Two years after the first data collection, this was repeated in four of the villages with 301 test subjects.
Gut Flora Provides Clues to Relationship Status
After correlating this social and biological data, they found that people who are connected by many different types of relationships (even outside the family or shared home) showed similarities in the composition of their gut flora. And stronger similarities than one would expect by chance.
Study co-author Francesco Beghini reports in a press release from the university: “We found clear evidence that microbiome exchange occurs between people who are not family and do not live together, even when we take into account other factors such as diet, water sources, and medication. In fact, microbiome exchange was the strongest predictor of people’s social relationships in the villages we studied, ahead of characteristics such as wealth, religion, or education.”2
With Whom Do We Share a Particularly Strong Bacterial Connection?
It should come as no surprise that spouses are in first place: The bacteria and fungi living in their gut are a 13.9 percent match. Close behind at 13.8 percent are people who live in the same household. People who regularly spend their free time together came in at ten percent, and close friends at 5.9 percent. People who lived in the same village but did not spend time together only had four percent similar intestinal flora. Between different villages, the value dropped again to two percent.
Other Influencing Factors
How often people spend time together is also crucial. Be it shared meals or the type of greeting, e.g., shaking hands, hugging, or kissing. This was associated with an increased exchange of microorganisms.
Villages as a Microbial Niche
The study results showed that certain clusters of bacterial species and strains occurred within groups in the villages. In other words, social networks represent niches in which individuals develop similar gut flora.
Co-author Jackson Pullman explains this using the example of the student community: “Imagine how different social niches form in a place like Yale. There are friend groups that focus on things like theater, team sports, or physics. Our study shows that the people who form these groups are connected in ways we never suspected before, even through their microbiome.”
Are Obesity and Depression Contagious?
The gut is often seen as the origin of several prevalent diseases, including obesity and diabetes, as well as mental health conditions like depression. From a positive perspective, we can, therefore, benefit from friends and our social network when it comes to our gut health. This assumes, of course, that they are in good health. Nonetheless, the findings also suggest that some microbiome-associated conditions may be more communicable than previously thought. Christakis speculates that “phenomena such as obesity could spread not only through social contagion, but also through biological contagion”.
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Classification of the study
It should be noted that the subjects were people in Honduras in a traditional setting with face-to-face interactions within a defined population that eats a traditional diet and is relatively free of antibiotics and other medications. These results are, therefore, not readily transferable to people in other countries and other lifestyles. Furthermore, the findings do not reflect any causal relationships. Future research will have to show whether obesity and other diseases can really be significantly transmitted via the microbiota.
In conclusion, it’s important to note that the study’s results should not lead you to isolate yourself from your social circle. Social contact can also transmit beneficial microbes and has other important functions. For example, spending time with friends and family is important for your mental well-being.