The Brain–Gut–Microbiome in Neuropsychiatric Disorders

Exploring how nutrition impacts the brain-gut-micriobiome in neuropsychiatric disorders. Carole Showell, DHsc (in progress), LCSW–

Author's Note: This is an excerpt from an academic paper written by the author. ChatGPT was used improve readability for a general audience.

Emerging research continues to highlight a powerful and often overlooked system influencing mental health: the brain–gut–microbiome axis. This bidirectional relationship between the gut and the brain plays a significant role in emotional regulation, cognitive functioning, and the development or maintenance of neuropsychiatric conditions.

At a foundational level, the health of gut microbial communities is shaped by diet. Nutrients such as polyphenols, dietary fiber, probiotics, and prebiotics—commonly found in leafy greens, fruits, whole grains, and fermented foods—support the diversity and stability of beneficial gut bacteria. This underscores a broader clinical and public health implication: access to and education about nutrient-dense foods is directly relevant to mental health outcomes.

Genetic Links and Microbial Patterns

Recent findings also suggest that genetic factors may interact with the gut microbiome in meaningful ways. O’Hare et al. (2025) analyzed data from the Shared Roots of Neuropsychiatric Disorders and Cardiovascular Disease Project and identified a positive association between the PROM2 rs2278067 T-allele and the presence of specific gut bacteria—including Mitsuokella, Odoribacter, Olsenella, and Catenibacterium—in individuals diagnosed with PTSD.¹

Notably, this genetic variant has also been linked to a range of neurodevelopmental, neurological, and psychiatric conditions. These findings align with prior research connecting gut microbiota to disorders such as anxiety, depression, and schizophrenia, suggesting that both biological predispositions and microbial composition may contribute to mental health vulnerability.

Interventions: Synbiotics and Beyond

Intervention-based research is beginning to explore how modifying the gut microbiome may improve psychological outcomes. Mitchell et al. (2026) conducted a quasi-experimental study examining synbiotics (a combination of probiotics and prebiotics) as an adjunctive treatment for autistic children.²

The study compared two groups: one receiving synbiotics alone and another receiving synbiotics combined with gut-directed hypnotherapy (GDH). Both groups showed improvements in gut microbiota composition, but the combined treatment group demonstrated sustained reductions in irritability and anxiety following the intervention. While more rigorous randomized controlled trials are needed, these findings suggest that microbiome-targeted interventions may hold clinical promise.

Diet as a Mental Health Intervention

Dietary patterns may offer one of the most accessible pathways for supporting gut and mental health. A systematic review by Dimopoulou et al. (2025) examined clinical trials across the lifespan and found consistent associations between dietary quality and mental health outcomes.³

The Mediterranean diet—rich in polyphenols, omega-3 fatty acids, and fiber—was associated with improved mood and reduced symptoms of anxiety and depression. Similarly, the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND diet) emphasizes foods such as leafy greens, berries, whole grains, legumes, olive oil, and nuts. In individuals experiencing chronic stress and fatigue, adherence to this diet was associated with reductions in C-reactive protein (a marker of inflammation) and improvements in mood.

These findings reinforce a key point: nutritional access and dietary education are not peripheral to mental health care—they are central to it.

Clinical Implications

Taken together, this body of research suggests that mental health cannot be fully understood or treated in isolation from physiological systems such as the gut microbiome. For clinicians, this opens the door to more integrative approaches that consider:

• Nutritional patterns

• Microbiome health

• Inflammatory processes

• Neurobiological mechanisms

While the field is still evolving, the evidence increasingly supports the inclusion of gut health in both assessment and intervention planning.

Footnotes

1. M. A. O’Hare et al., “Preliminary Insights Into the Relationship Between the Gut Microbiome and Host Genome in Posttraumatic Stress Disorder,” Genes, Brain & Behavior 24, no. 3 (2025): 1–9, https://doi.org/10.1111/gbb.70025.

2. L. K. Mitchell et al., “Gastrointestinal, Behaviour and Anxiety Outcomes in Autistic Children Following an Open Label, Randomised Pilot Study of Synbiotics vs Synbiotics and Gut-Directed Hypnotherapy,” Journal of Autism & Developmental Disorders 56, no. 3 (2026): 1027–1045, https://doi.org/10.1007/s10803-024-06588-9.

3. M. Dimopoulou, A. Dimopoulou, and O. Gortzi, “Dietary Patterns and Mental Health Across the Lifespan: A Systematic Review of Randomized Clinical Trials,” Psychology International 7, no. 4 (2025): 87, https://doi.org/10.3390/psycholint7040087.