The Effect of Synbiotic Supplementation on Self-Reported Aggression in Healthy Adult Men: A Randomized, Double-Blind, Placebo-Controlled Trial

Background: There is a positive relationship between aggressive behaviors and gut microbiota composition. The present study aimed to investigate the effect of synbiotic supplementation on self-reported aggression in healthy adult men. Methods: This double-blind randomized controlled clinical trial was conducted on 100 healthy adult men working at Iran University of Medical Sciences. Members of synbiotic group (SG) received 2 capsules daily containing 500 mg of synbiotic (Familact) and members of placebo group (PG) received 2 placebo capsules daily for 8 weeks. The intensity of aggression (verbal, physical aggression, hostility, and anger), depression, anxiety and stress, food intake, physical activity, and anthropometric indicators were measured at the beginning and end of the study. Statistical analysis of data was done using SPSS software version 26. P-value <0.05 was considered significant. Results: Thirty people completed the study. The synbiotic supplement caused a significant decrease in total aggression at the end of the intervention, compared to PG (P=0.04). Moreover, verbal aggression decreased in both groups compared to the beginning of the study, while it was significant in SG (P=0.005). There was no difference in the intensity of physical aggression, anger, and hostility after intervention. Conclusion: Synbiotics may be useful in reducing self-reported aggression in healthy adult men.