Summary
This narrative review in Nature Mental Health (2025) critically examines the distinction between causal, correlative and bidirectional relationships between the gut microbiota and mental health. The authors, a consortium of leading researchers in the microbiota–brain axis field, appraise the evidence base to clarify which observed associations represent genuine mechanistic causation versus confounding or reverse causation. The work contributes to resolving a key methodological challenge in interpreting microbiota–psychiatry research.
Regional applicability
The mechanistic framework presented is applicable to United Kingdom clinical and research settings, particularly as the NHS increasingly considers gut health interventions for mental health support. However, as this is a review of global evidence, localisation would require assessment of whether UK population microbiota patterns and dietary factors align with the mechanistic conclusions drawn from international cohorts.
Key measures
Mechanistic pathways linking gut microbiota to mental health; types of evidence (causal vs correlative); bidirectional signalling mechanisms
Outcomes reported
The study examined and distinguished causal, correlative and bidirectional relationships between gut microbiota composition and mental health outcomes. As suggested by the title, the work synthesises evidence on how microbial communities influence psychiatric and neuropsychological conditions.
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