Article image

Gut bacteria influence our social behavior and sense of fairness

The gut microbiota — a diverse ecosystem of bacteria, viruses, and fungi within our digestive tract — plays a crucial role in our health, influencing more than just digestion. Recent research has revealed our microbiome’s significant impact on cognitive functions, emotions, sense of fairness, and even our social behaviors.

Gut microbiota and social behavior

Studies involving animals have provided compelling insights. For example, mice raised in sterile conditions, free of microbial life, exhibit difficulties in social interactions. This finding hints at a profound, essential link between our gut microbiota and social behavior.

However, applying these animal-based findings to human health is complex. Researchers are still exploring the specific neuronal, immune, and hormonal pathways that enable the gut microbiota to communicate with the brain.

Although a correlation between the composition of the gut microbiota and fairness has been noted, the exact mechanisms remain unclear, leaving scientists to continue unraveling this intricate relationship.

Understanding the gut-brain connection

Hilke Plassmann of Sorbonne University and Insead, leading the Control-Interoception-Attention Team at the Paris Brain Institute, sheds light on potential pathways for this interaction.

“The intestinal ecosystem communicates with the central nervous system via various pathways, including the vagus nerve,” Plassmann notes.

This communication might also involve biochemical signals that prompt the release of neurotransmitters like dopamine and serotonin, crucial for brain health.

Fairness and decision-making from the gut

To explore whether the human gut microbiota directly influences decision-making, Plassmann and her team turned to the “ultimatum game,” a behavioral test that measures responses to fairness.

In this game, one player divides a sum of money between themselves and another player, who can reject the offer if it feels unfair, leaving both players with nothing.

This scenario tests “altruistic punishment,” where rejecting an unfair offer serves to uphold equality over personal gain.

The study involved 101 participants, split into two groups over seven weeks. One group received dietary supplements containing probiotics and prebiotics, while the other received a placebo. Both groups played the ultimatum game at the start and end of the study period.

Enhanced fairness through gut health

The findings were compelling. By the study’s conclusion, the supplemented group significantly rejected more unequal offers, demonstrating an enhanced sensitivity to fairness, compared to the placebo group, which showed no change in behavior.

Biological assessments provided further intrigue. Participants who initially had a greater bacterial imbalance showed the most pronounced changes in their gut microbiota and the highest sensitivity to fairness after supplementation.

Notably, these participants also exhibited a decrease in tyrosine levels, a precursor to dopamine, suggesting a potential biological mechanism at play.

Potential and challenges of microbiota

While it’s premature to claim that gut bacteria can alter our rationality and openness to social considerations, Plassmann remains optimistic about the research directions. “These new results clarify which biological pathways we must look at,” she remarks.

The idea that dietary modifications could influence our decision-making and fairness by altering our gut microbiota opens up exciting possibilities for future research, emphasizing the need for careful exploration in this field.

This burgeoning area of study not only highlights the complexity of human biology but also points to innovative ways we might someday enhance our social interactions and mental health through dietary choices, guided by an understanding of our microbiota.

The journey to fully understand the influence of our internal ecosystems on our behavior and decision-making continues, promising intriguing insights and potential interventions in the realms of psychology and neuroscience.

More on gut microbiota

Beyond decision making and fairness, the gut microbiota has been linked to numerous health conditions and diseases. Studies show it influences obesity, diabetes, and cardiovascular health.

An imbalance in gut bacteria, known as dysbiosis, is associated with autoimmune diseases like Crohn’s disease and rheumatoid arthritis. Emerging evidence suggests a role in cancer development and response to therapies.

Additionally, gut microbiota impacts mental health, with links to anxiety, depression, and autism spectrum disorders. Diet, antibiotics, and lifestyle significantly affect the gut microbiome.

Ongoing research aims to harness this knowledge for personalized medicine, probiotics, and dietary interventions to promote overall health and prevent disease.

The full study was published in the journal PNAS Nexus.


Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and


News coming your way
The biggest news about our planet delivered to you each day