Gut microbiota is made up of thousands of billions of microorganisms living mainly in the intestines, in symbiosis with the body. They are mainly bacteria, but also yeasts and viruses.
This “flora”, as it is also known, has an impact on digestive function, but it could also influence our behaviour, certain emotions, and even decision-making, according to the findings of researchers at the Paris Brain Institute in France and the University of Bonn in Germany.
This is not the first study to explore this association, though most of the previous research has only involved animals. “The available data suggests that the intestinal ecosystem communicates with the central nervous system via various pathways, including the vagus nerve.
“It might also use biochemical signals that trigger the release of neurotransmitters, such as dopamine and serotonin, which are essential for proper brain function,” said study co-author Hilke Plassmann from the Paris Brain Institute.
With this in mind, the researchers carried out behavioral tests on 101 men aged between 20 and 60. These tests included the “ultimatum game”, which evaluates an individual’s decision-making and sensitivity to fairness or unfairness.
The rules are simple: one participant is given a sum of money and asked to share it – fairly or unfairly – with a second participant. The latter can accept or decline the offer, depending on whether it seems fair or unfair. If deemed unfair, neither player receives the reward.
Notably, 51 participants took probiotics and prebiotics – used to rebalance intestinal flora – for seven weeks, while 50 received a placebo. All participants took part in the game during two sessions, at the start and at the end of the supplementation period.
Published in the journal PNAS Nexus, the results suggest that the composition of gut microbiota may influence not only decision-making but also “sensitivity to fairness”.
In detail, the researchers explained that participants who had taken pro- and prebiotics were more likely to refuse offers considered unequal. This change in decision-making and sensitivity to un/fairness was not observed in the placebo group.
Participants who took supplements also experienced the greatest changes to the composition of their intestinal microbiota. Moreover, “the researchers also observed a sharp drop in the supplemented group’s levels of tyrosine, a dopamine precursor, after the seven-week intervention”, the study news release said.
“For the first time, a causal mechanism is emerging: the composition of the gut microbiota could influence social behaviour through the precursor of dopamine, a neurotransmitter involved in brain-reward mechanisms,” it added.
This finding is likely to give rise to further, more targeted research. “It’s too early to say that gut bacteria can make us less rational and more receptive to social considerations,” Plassmann noted. “However, these new results clarify which biological pathways we must look at.
“The prospect of modulating the gut microbiota through diet to positively influence decision-making is fascinating, so we need to explore this avenue very carefully.”