Gut microbiome, diet, and attention-deficit/hyperactivity disorder

Abstract

Introduction: Attention-deficit/hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder shaped by both genetic and environmental factors. The gut microbiome and diet have attracted particular interest as potentially modifiable components of the microbiota-gut-brain axis. Objective: This review aimed to critically evaluate the evidence on the role of the gut microbiome in ADHD, the potential mechanisms involved, and the influence of dietary patterns and nutritional interventions. Methodology: We searched PubMed/MEDLINE, Scopus, and Web of Science for studies published up to 31 July 2026. Given the heterogeneity of the available evidence, we synthesised the findings thematically. Results: Studies to date have reported differences in gut microbial diversity, the abundance of specific bacterial and fungal taxa, and short-chain fatty acid concentrations. However, no consistent microbiome profile associated with ADHD has yet been identified. Proposed mechanisms linking the gut microbiome to ADHD include altered intestinal barrier permeability, immune and metabolic signalling, vagal pathways, and the metabolism of neurotransmitter precursors. Diets high in processed foods have been associated with more pronounced ADHD symptoms and a less favourable gut microbiota composition. Evidence for the potential benefits of the Mediterranean dietary pattern, however, comes largely from observational studies. A few-foods diet may benefit some children when implemented under professional supervision. Findings on probiotics, kefir, omega-3 fatty acids, and micronutrient supplementation remain inconsistent. Conclusion: The microbiome and diet are biologically plausible but, as yet, insufficiently established components of the heterogeneous pathophysiology of ADHD. Nutritional interventions should be individualised and used alongside standard treatment, with appropriate monitoring of nutritional status and safety.