Improving ADHD core symptoms and individual quality of life with dietary approaches through microbiota-gut-brain signalling (the ADAPT study): a prospective, randomized controlled trial

Diet influences the gut microbiota, which in turn affects gut–brain signalling and may contribute to attention-deficit hyperactivity disorder (ADHD) pathophysiology. A microbiota-targeted diet rich in fibre and fermented foods has the potential to support microbial function and improve ADHD symptoms, offering an alternative or adjunctive pharmacological treatment where efficacy is limited. The Improving ADHD core symptoms and individual quality of life with Dietary APproaches Through Microbiota-Gut-Brain Signalling (ADAPT) study is a prospective, participant-blind, observer-blind, parallel arm, randomized trial designed to evaluate the effects of microbiota-targeted dietary intervention on ADHD symptoms and related outcomes over a 12-week intervention period, with an optional follow-up at 3-months after the end of the intervention. Adults with and without ADHD ( n = 100/group) will be randomized to either a combination intervention diet high in fibre and fermented foods (minimum 25 g of fibre and minimum of 3 servings of fermented foods daily) or a control diet (standard Irish dietary guidelines). The primary outcome will be changes in ADHD symptoms assessed using Conner’s Adult ADHD Rating Scale (CAARS). Secondary outcomes include neurocognitive function, mood, evaluation of goals individually established by participants, sleep, eating behaviour, gut microbial profile, inflammatory and immune markers, and cortisol and a wide range of metabolites and protein in blood samples. Significant improvements in ADHD symptoms measured by CAARS, alongside enhanced neurocognitive function and mood, would support the effectiveness of the microbiota-targeted diet in adults with ADHD. Alterations in gut microbial composition and function, as well as correlations with symptom improvement, would provide insights into the role of diet in ADHD management. Findings related to sleep, eating behaviour, immunity and inflammation, cortisol regulation and protein and metabolite alterations would further elucidate the broader impact of diet on ADHD and overall well-being with the microbiome-gut-brain axis framework. (NCT07376746||https://www.clinicaltrials.gov/||Registered in 21-01-2026) with the Clinical Trial Registry [1].