Recent insights into the role of the human microbiota on the brain and cognitive functioning have led to the hypothesis that the probiotic ‘Ecologic Barrier’ may decrease aggressive behavior and/or...Show moreRecent insights into the role of the human microbiota on the brain and cognitive functioning have led to the hypothesis that the probiotic ‘Ecologic Barrier’ may decrease aggressive behavior and/or thoughts. The aim of the current study was to investigate the effect of a 4-week multispecies probiotic intervention on self-reported aggressive behavior and thought patterns in healthy individuals, whether there are differences between males and females, and to investigate whether HRV has an influence on the efficacy of the intervention with probiotics. HRV is a physiological phenomenon of the variation in the time interval between heartbeats. Low HRV can be related to impaired behavioral regulation and reduced behavioral inhibition, which is related to aggressive behavior, and therefore this can be a mediating variable in the design of this study. Individuals with a low HRV could benefit more from the intervention with probiotics than individuals with a high HRV and could expect a greater decrease in aggressive behavior and/or thoughts. In a double-blind, placebo-controlled, randomized, pre-and post-intervention assessment, between-subjects design, 25 healthy participants received a 4-week probiotic food-supplement intervention with the multispecies probiotics, while 25 control participants received an inert placebo for the same period. In the pre- and post-intervention assessment, self-reported aggressive behavior and thoughts were assessed using the Aggression Questionnaire and the aggression subscale of the LEIDS-r, the Leiden Index for Depression Sensitivity. The 4-week multispecies probiotic intervention did not reduce physical aggression, verbal aggression, anger, hostility, overall aggression scores or aggressive thought patterns. A slight decrease in aggressive behavior and aggressive thoughts can be seen on a few subscales in the probiotics group, but the results were not significant. An exploratory finding was found: participants with a decreased HRV compared to the pre-intervention measurement, scored higher on verbal aggression during the post-intervention; a strong negative correlation was found. However, HRV appeared to have no influence on the efficacy of the intervention with probiotics. These results provide evidence that a low HRV could be linked to higher verbal aggression. Previous research has shown that there could be a difference in aggression between men and women, for example through male hormones, and therefore future studies should investigate why self-reported aggressive behavior and thoughts in males and females may respond differently to probiotics. The sample used for this study was pre-dominantly female and this could be an explanation for the fact that no difference was found. This study has some limitations that may have led to these results. A lot of research has been done on mice, research that cannot simply be translated into humans. This study did not include the exact influence of stress and the use of HRV, regulated by efferent fibers of the vagal nerve, to determine the influence and effectiveness of probiotics can be questioned because probiotics activate the afferent fibers of the vagal nerve . Furthermore, we work with self-reported aggressive behavior among participants without clinical aggression scores. In the future, research could be done into the influence of probiotics on aggression within the clinical population.Show less
