The stress experienced during competitive social situations negatively affects the gut microbiome. The experiment was performed in Syrian hamsters, animals that compete to establish hierarchies of dominant and subordinate groups. The study analyzed gut bacteria before the hamsters met and after they had competed for hierarchical placement, then compared these samples to a control group of hamsters that lived in an already established group. In the study, even a single exposure to social stress altered the gut microbiota, significantly decreasing gut bacteria diversity and composition. Repeated exposure to stress resulted in greater negative impacts on the microbiome. There was no significant difference in alterations between winners and losers; social stress in both groups led to similar changes, although the specific bacteria impacted were different between the two groups. Interestingly, higher levels of some bacteria predicted whether an animal would become a winner or loser. Behavioral Brain Research

→Takeaway: Researchers say that this supports the idea of bi-directional communication – stress impacts gut bacteria, and the composition of gut bacteria also impacts the stress response.