Background Gut microbial community, which may influence our mood, can be shaped by modulating the gut ecosystem through dietary strategies. Understanding the gut–brain correlationship in healthy people is important for maintenance of mental health and prevention of mental illnesses.

Methods A case study on the correlation between gut microbial alternation and mood swing of healthy adults was conducted in a closed human life support system during a 105‐day experiment. Gut microbial community structures were analyzed using high‐throughput sequencing every 2 weeks. A profile of mood states questionnaire was used to record the mood swings. Correlation between gut microbes and mood were identified with partial least squares discrimination analysis.

Key Results Microbial community structures in the three healthy adults were strongly correlated with mood states. Bacterial genera Roseburia, Phascolarctobacterium, Lachnospira, and Prevotella had potential positive correlation with positive mood, while genera Faecalibacterium, Bifidobacterium, Bacteroides, Parabacteroides, and Anaerostipes were correlated with negative mood. Among which, Faecalibacterium spp. had the highest abundance, and showed a significant negative correlation with mood.