Changes in the gut microbiome may significantly impact social decision-making and behavior, according to the results of a new study.
Published in PNAS Nexus, the randomized, double-blind, placebo-controlled trial of consisted of 101 male participants followed for 7 weeks. Participants completed a 3-day food diary, arrived fasted, and provided fecal and blood samples before eating a standardized breakfast. Half of the study participants received probiotics and prebiotics. Each session included behavioral tasks, physical exams (blood pressure, height, weight, body fat, water), and brain measures (fMRI and diffusion-weighted imaging).
Researchers found participants who received the probiotics and prebiotics, were more likely to reject unfair monetary offers (30%-40% split vs. 50% or more) than those who did not, a behavior noted as altruistic punishment.
“A large body of evidence shows that social decisions are not influenced solely by self-interest but also by social norms such as fairness considerations. For example, the concept of altruistic punishment describes forgoing personal interest to penalize behavior that is not in line with social norms,” noted researchers. “Fairness became more important when deciding to accept or reject different monetary payoffs.”
The researchers linked the behavioral changes to alterations in fasting-state serum levels of tyrosine, a dopamine precursor, suggesting a potential mechanistic link along the gut–microbiota–brain axis. They also noted, participants with a higher baseline Firmicutes to Bacteroidetes (ratio, indicative of an unbalanced gut microbiome, experienced more significant changes in gut microbiome composition and social decision-making, suggesting the intervention's effectiveness may depend on the initial gut microbiome balance.
Previous research suggested the gut microbiome is “altered in clinical conditions linked to socio-affective processes such as depression, anxiety, and autism,” noted researchers. “Future studies could test whether the gut microbiome could serve as a target for interventions to improve social decision-making in health and disease.”
Full disclosures can be found in the study.
