Gut feeling: diet trial targets ADHD symptoms through Gut-Brain link

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

ADHD Group Inclusion Criteria: 1. Be able to give written informed consent 2. Should be stable for 4 weeks on psychopharmacological medication or without medication 3. Should have an established diagnosis of ADHD or ADD as the main mental disorder diagnosis. This will be validated by the ADHD diagnostic criteria after DSM-5, with the DIVA interview. 4. Aged 18-50 years 5. Fluency in English language Control Group Inclusion Criteria 1. Be able to give written informed consent 2. Should be stable for 4 weeks on any medication for physical health or without medication 3. Should not currently taking psychopharmacological medicine or discontinued psychopharmacological medicine in the past 6 months (due to relapse risk) 4. Should NOT have an established diagnosis or clinical symptoms of ADHD or ADD. This will be validated using with the ASRS-6 (\< 4) 5. Should not have a diagnosis of ASD as indicated by self-report. 6. Not have current, or in the past 2 years, symptoms or diagnosis of a depressive disorder, bipolar spectrum disorder, OCD, PTSD, generalised anxiety disorder, severe alcohol or illegal drug dependency, psychotic disorder, anorexia nervosa, and bulimia nervosa 7. Not have current symptoms or diagnosis of a panic disorder or social anxiety disorder that is not currently being treated by a psychotherapist or other mental health care professional 8. Aged 18-50 years 9. Fluency in English language ADHD and Control Group Exclusion criteria: 1. Current severe depressive (PHQ-9\>15), manic or psychotic episode, acute suicidality or suicide attempt in the past 3 months, current severe alcohol and illegal drug dependency as determined by the MINI Psychiatric Interview or clinical diagnosis. 2. Pregnant, breastfeeding, or planning to be pregnant. 3. Habitual fibre intake exceeding 25g/day. 4. Allergy to intervention foods. 5. Allergy to local anaesthesia (only if opting for the skin punch). 6. Taking anticoagulant medication or have coagulation disorder like haemophilia (only if opting for the skin punch). 7. Have a BMI below 18.5 kg/m2. 8. Current diagnosis or symptoms of anorexia nervosa or bulimia nervosa, as determined by clinical diagnosis or on the MINI. 9. Have a significant acute or chronic coexisting illness (cardiovascular, gastrointestinal, endocrinological, immunological, metabolic) or any condition which contraindicates, in the investigator's judgement, entry to the study. 10. Taking antibiotics in the past month (washout period of 1 month is required). 11. Taking medication that the investigator believes would interfere with the objectives of the study, pose a safety risk or confound the interpretation of the study results; to include anti-inflammatory drugs, corticosteroids, laxatives, enemas, anti-coagulants, and over-the counter non-steroidal analgesics. Participants should have a wash-out period of one month. 12. Individuals who, in the opinion of the investigator, are considered to be poor attendees or unlikely for any reason to be able to comply with the trial. 13. Participants receiving treatment involving experimental drugs. Washout period of one month is required. 14. Current prebiotic or probiotic supplement use (a wash-out period of 4 weeks after cessation will allow entry to the study). 15. Previous participation in the Diet Study (APC150) 16. Uncorrected vision. 17. A history of any other condition affecting cognitive function (besides ADHD or ASD for ADHD group participants). The specific exclusion criteria for electroencephalography (EEG) recording for both the ADHD and Control groups are as follows: 1. Left-handedness, 2. Non-removable medical devices such as pacemakers, hearing aids, cochlear implants, or deep brain stimulators, 3. Hairstyles that prevent access to the scalp, and 4. Skin conditions on the scalp. Participants who meet these exclusion criteria for the EEG portion of the study will still be included in the overall study but will not undergo EEG recording and will instead complete neurocognitive tasks outside of EEG recording.