New research finds interesting associations between gut bacterial diversity and personality traits, such as sociability and neuroticism. The findings also draw attention to the potential benefits of eating foods rich in pre- and probiotics.
Katerina Johnson, Ph.D., from the Department of Experimental Psychology at Oxford University, United Kingdom, set out to examine if there was a connection between the composition of the gut bacteria and personality traits such as sociability and neuroticism.
She explains the motivation for her research, saying, “There has been growing research linking the gut microbiome to the brain and behavior, known as the microbiome-gut-brain axis.”
“Most research has been conducted in animals, while 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.”
To this end, Johnson collected fecal samples from 655 adults, 71% of whom were female and 29% male, with an average age of 42. The scientists used 16S rRNA gene sequencing analysis to examine abundances of specific bacterial genera.
The study involved asking the participants to answer a comprehensive study questionnaire that inquired about their behavior, health, lifestyle, and sociodemographic factors.
Johnson carried out a set of statistical analyses, which helped determine the relationship between the composition of the gut bacteria and behavioral traits such as sociability and neuroticism.
The scientist published her results in the Human Microbiome Journal.
More specifically, the researcher used the International Personality Item Pool — which consists of 50 items — to assess personality traits based on the “five-factor model of personality.”
This model suggests that differences in personality are grouped under five main domains, or the “Big Five:”
- extraversion, or the “propensity to seek and enjoy others’ company”
- agreeableness, defined as “trust and cooperation in social interactions”
- conscientiousness, or the “attention to detail and focus”
- neuroticism, i.e., the “tendency to feel negative emotions”
- openness, which researchers have described as “creativity, intellectual curiosity, and willingness to seek new experiences”
Johnson applied multiple regression analyses of the bacterial taxa and adjusted for key variables that scientists know influence the composition of the gut bacteria, and that may have otherwise confounded the results.
These variables were sex, age, body mass index (BMI), birth delivery mode, infant feeding method, use of oral antibiotics in the last 6 months, gut conditions, and use of probiotic supplementation.
Johnson adjusted for these potential confounders only in a subset of 261 participants who had provided the necessary information.
The study revealed that various types of bacteria that researchers had linked with autism spectrum disorder in past studies also had associations with sociability differences 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,” explains the study’s author.
Furthermore, the study found that people with more extensive social networks were more likely to have a more diverse composition of gut bacteria. This suggests, writes the author, that being socially active may promote the diversity of the gut microbiome.
Many people believe that greater diversity in the human gut microbiome promotes gut health and better overall 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. This result suggests the same may also be true in human populations.”
– Katerina Johnson
By contrast, the analysis revealed that lower microbial diversity was associated with higher levels of stress and anxiety.
Furthermore, an intercorrelation analysis “revealed that people who ate more foods with naturally occurring probiotics or prebiotics had significantly lower levels of anxiety, stress, and neuroticism and were also less likely to [develop] a mental illness.”
However, the researcher did not find the same correlation with probiotics or prebiotics in supplement form.
Natural sources of probiotics include fermented cheese, sauerkraut, kimchi, and natural sources of prebiotics include bananas, legumes, whole grains, asparagus, onion, and leek.
Another intriguing finding was that people who had been fed formula as infants had a less diverse gut microbiome.
“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,” says Johnson.
“Our modern-day living may provide a perfect storm for dysbiosis [i.e., an imbalance in the microbiota] of the gut,” adds Johnson.
“We lead stressful lives with fewer social interactions and less time spent with nature; our diets are typically deficient in fiber, we inhabit over-sanitized environments and are dependent on antibiotic treatments.”
– Katerina Johnson
“All these factors can influence the gut microbiome and so may be affecting our behavior and psychological well-being in currently unknown ways.”
The scientist, however, also acknowledges a limitation of her research. She says, “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.”