A new large study finds that some of our personality traits may be linked to the composition and diversity of our gut bacteria (microbiome). The findings are published in the Human Microbiome Journal.

“There has been growing research linking the gut microbiome to the brain and behaviour, known as the microbiome-gut-brain axis,” said Dr. Katerina Johnson, who conducted her Ph.D. in the Department of Experimental Psychology at the University of Oxford in the U.K.

“Most research has been conducted in animals, whilst studies in humans have focused on the role of the gut microbiome in neuropsychiatric conditions. In contrast, my key interest was to look in the general population to see how variation in the types of bacteria living in the gut may be related to personality.”

Prior research has linked the gut microbiome to autism (a condition characterized by impaired social behavior). Johnson’s study suggests that numerous types of bacteria previously linked to autism are also related to differences in sociability in the general population.

“This suggests that the gut microbiome may contribute not only to the extreme behavioral traits seen in autism but also to variation in social behavior in the general population. However, since this is a cross-sectional study, future research may benefit from directly investigating the potential effect these bacteria may have on behavior, which may help inform the development of new therapies for autism and depression,” said Johnson.

One interesting finding was that people with larger social networks tend to have a more diverse gut microbiome, which is often associated with better gut health and general health.

“This is the first study to find a link between sociability and microbiome diversity in humans and follows on from similar findings in primates which have shown that social interactions can promote gut microbiome diversity,” said Johnson. “This result suggests the same may also be true in human populations.”

Conversely, the study shows that people with higher stress or anxiety had a lower microbiome diversity. In addition, the researchers found that adults who had been formula-fed as children had a less diverse microbiome in adulthood.

“This is the first time this has been investigated in adults and the results suggest that infant nutrition may have long-term consequences for gut health,” said Johnson.

Diversity was also positively related to international travel, perhaps due to exposure to novel microbes and different diets. More adventurous eaters had a more diverse gut microbiome whilst those on a dairy-free diet had lower diversity.

In addition, diversity was greater in people with a diet high in natural sources of probiotics (e.g. fermented cheese, sauerkraut, kimchi) and prebiotics (e.g. banana, legumes, whole grains, asparagus, onion, leek), but notably not when taken in supplement form.

“Our modern-day living may provide a perfect storm for dysbiosis of the gut. We lead stressful lives with fewer social interactions and less time spent with nature, our diets are typically deficient in fibre, we inhabit oversanitized environments and are dependent on antibiotic treatments. All these factors can influence the gut microbiome and so may be affecting our behavior and psychological well-being in currently unknown ways,” said Johnson.

Source: University of Oxford