Researchers from the Paris Brain Institute and the University of Bonn tracked how shifts in the gut microbiota can shape judgments about fairness and interpersonal behavior. The study, published in a leading scientific journal, explores the connection between gut health and decision making and offers new clues about how internal microbial communities influence human choices.
The intestinal microbiota comprises bacteria, viruses, and fungi residing in the digestive tract. Emerging evidence links its composition to cognitive function, stress responses, and symptoms of anxiety and depression, underscoring its potential role in mental well-being and behavior.
In the recent experiment, a cohort of 101 volunteers participated. Half received a seven-week course of probiotics and prebiotics designed to support beneficial gut bacteria, while the other half took a placebo. The researchers then formed pairs to play a fairness-based decision game. In this setup, one participant could determine the division of a monetary sum, while the other could either accept the offer or reject it. If the offer was rejected, the entire amount would be forfeited.
Findings indicated that participants taking the microbial supplements were more prone to rejecting unfair divisions, even when that decision was not in their immediate material interest. They appeared to act less rationally in the context of the game compared with the placebo group, who more frequently accepted proposed distributions when they were fair or moderately favorable.
The team also observed a notable drop in tyrosine levels among those receiving the supplements. Tyrosine is a chemical precursor to dopamine, a neurotransmitter closely tied to reward processing and motivation in the brain. Lower tyrosine levels could influence how people perceive rewards and punishments, potentially altering decision-making processes in social economic tasks.
These observations provide a potential mechanism for how gut microbes might influence human decisions. By modulating neurotransmitter pathways or related metabolic signals, the gut microbiota could shape responses to fairness, risk, and social cooperation, offering insight into why individuals sometimes make choices that seem counterintuitive to their financial self-interest.
Earlier microbiology research suggested that gut microbes can serve as a kind of backup for liver function, reflecting the broad metabolic reach of the intestinal ecosystem. The new findings contribute to a growing body of work showing the gut-brain axis as a dynamic interface where diet, resident microbes, and neural processes intersect to influence behavior and cognitive processes in everyday life.