Emotional well-being and gut microbiome profiles by enterotype

The gut microbiome's role in mental and physical health is increasingly recognized, with bidirectional communication between the gut and brain via the brain-gut-microbiota axis. Emotional disorders often coincide with gastrointestinal issues, suggesting a connection. Studies in rodents demonstrate that gut microbiota alterations affect emotional behaviors. Clinical evidence shows altered gut microbiota composition in patients with major depressive disorder (MDD), and links between favorable personality traits and gut microbiota composition and diversity in healthy adults. The concept of "psychobiotics"—beneficial bacteria and dietary fibers enhancing mental well-being—further supports this connection. Studies show that probiotic intake improves positive affect and reduces anxiety and depression symptoms. Enterotypes, robust clusters based on gut microbiota composition (*Bacteroides*, *Prevotella*, *Ruminococcus*), are suggested as potential moderators in this relationship. Previous research indicates that enterotypes might influence emotional processing and quality of life. This study aimed to assess the association between emotional well-being and gut microbiota profiles in healthy Korean adults, focusing on the potential moderating role of enterotypes. The hypothesis was that gut microbiome profiles are associated with emotional well-being, with differential roles by enterotype.

Existing literature highlights the strong correlation between gut microbiota and mental well-being. Studies have demonstrated links between gut dysbiosis and various mental health conditions including depression, anxiety, and autism spectrum disorder. Microbiota diversity, reflecting ecosystem stability and resilience, is considered a key marker of gut health. Several studies have identified associations between factors influencing emotional well-being (stress, anxiety, socioeconomic status, social integration, and personality traits like openness) and gut microbiota diversity. However, the specific mechanisms and the role of enterotypes in these relationships remain under-investigated. This study aims to contribute to the growing body of evidence exploring the interplay between emotional well-being, gut microbiome composition, and enterotype classification.

This study utilized data from the Korean Adult Longitudinal Study (KALS), a subset of 83 participants who provided stool samples and completed surveys. Emotional well-being was assessed using the Positive Affect and Negative Affect Schedule (PANAS), measuring positive and negative affect on a 5-point Likert scale. Participants also reported abdominal pain levels, stool consistency (Bristol Stool Scale), antibiotic use, and dietary preferences. Gut microbiome profiles were obtained via high-throughput 16S rRNA gene sequencing. Data analysis included principal coordinate analysis (PCOA) for clustering based on gut microbiome composition, identifying two enterotypes: *Bacteroides*-dominant (E1) and *Prevotella*-dominant (E2). Linear discriminant analysis effect size (LEfSe) confirmed differential microbial abundance between clusters. Alpha diversity (Shannon, Observed, Chao1, ACE) was compared between enterotypes using independent sample t-tests and linear regression, controlling for age, sex, and antibiotic use. The association between alpha diversity and PANAS scores, considering enterotype as a moderator, was analyzed using generalized linear models. MaAsLin2 analysis identified genera significantly correlated with mood status, controlling for confounding factors.

Principal coordinate analysis revealed two distinct enterotypes: *Bacteroides*-dominant (E1, n=49) and *Prevotella*-dominant (E2, n=34). The *Prevotella* group showed significantly higher species richness (Observed, Chao1, ACE) than the *Bacteroides* group. However, the Shannon diversity index did not differ significantly between the two groups. Importantly, the Shannon diversity index was significantly associated with positive affect scores but not negative affect scores in the overall population. This association between positive affect and Shannon diversity index was significantly stronger in the *Prevotella*-dominant group (E2) than in the *Bacteroides*-dominant group (E1). The positive affect scores measured one and a half years prior to stool collection also showed a similar pattern of association with the Shannon index, particularly in the *Prevotella* group. MaAsLin2 analysis identified *Agathobaculum* and *Collinsella* as significantly associated with negative and positive affect, respectively. A novel genus from the Lachnospiraceae family (PAC001043_g) showed a positive correlation with positive affect and a negative correlation with negative affect.

This study's findings support the hypothesis that gut microbiome diversity is related to emotional well-being, and that this relationship is moderated by enterotype. The stronger association between positive affect and gut diversity in the *Prevotella*-dominant group aligns with previous research indicating a higher emotional response and brain connectivity in this enterotype. The findings suggest a tighter link between "feeling good" and gut microbiota well-being, especially under *Prevotella*-dominant conditions. The identification of specific genera associated with emotional well-being, including a novel Lachnospiraceae genus, offers promising avenues for future research on psychobiotics and targeted interventions.

This study demonstrates a link between emotional well-being and gut microbiome diversity and composition, particularly when stratified by enterotype. The enterotype-specific association between positive affect and gut microbiota diversity suggests potential for personalized interventions. Further research is needed to elucidate the mechanisms underlying this communication and to explore the therapeutic potential of modulating the gut microbiome to improve mood disorders.

The cross-sectional design limits causal inferences. The relatively small sample size, especially within each enterotype, could have reduced statistical power. Enterotype classification methods may influence results. The lack of detailed health status and dietary data may have introduced confounding factors. Future studies should address these limitations with longitudinal designs, larger samples, and more comprehensive data collection.