NMB: The Impact of Diet on the Gut-Microbiota-Brain Axis

University College Cork (Other)
Overall Status
CT.gov ID

Study Details

Study Description

Brief Summary

This study aims to investigate the effects of an 8-week dietary intervention on cognitive function, stress, and the gut microbiota in healthy adults with low fibre intake.

Condition or Disease Intervention/Treatment Phase
  • Other: Fermented Foods
  • Other: High Fibre
  • Other: Combined Diet
  • Other: Control

Detailed Description

The gut microbiota communicates bidirectionally with the brain via the microbiota-gut-brain axis to influence various aspects of human physiology, including host metabolism, immune function, behaviour, and cognition. Diet is a key modulator of the microbial composition, suggesting that the microbiota could explain the association between poor nutrition and decreasing health of the population. Dietary fibre is the main energy source for the gut microbiota and fundamentally impacts its composition and function. The microbiota-gut-brain axis has been proposed to mediate some of the effects of dietary fibre on the brain, for example through microbial metabolites (e.g., short-chain fatty acids (SCFA)), regulation of the immune system, and the microbial impact on gut hormones and neurotransmitters. Similarly, intake of fermented foods is positively associated with cognitive health and has been shown to alter the microbiota composition and function and exert an anti-inflammatory effect. However, no studies to date have examined the singular and combined effects of fermented and fibrous foods on the gut microbiota, cognition, and emotion. The present study aims to determine the role of diet on the microbiota-gut-brain axis and mental health.

Using a randomized-controlled, parallel, single-blinded design, participants consuming a habitually low fibre diet (N=200) will undergo an 8-week dietary intervention. Participants will receive one of four diets (n=50 in each group): high fibre (aim 24-35 grams/day), fermented foods (aim 4-6 portions/day), combined diet of fermented foods and high fibre (aim 25-30g/day of fibre and 3-4 servings/day of fermented foods) or control (dietary education according to national Irish guidelines). Cognitive, psychological, and biological measures will be compared at baseline and endpoint. During the intervention period, individuals will provide repeated faecal samples to assess temporal microbial changes.

Study Design

Study Type:
Anticipated Enrollment :
200 participants
Intervention Model:
Factorial Assignment
Intervention Model Description:
Randomized-controlled, parallel, single-blinded designRandomized-controlled, parallel, single-blinded design
Single (Participant)
Primary Purpose:
Basic Science
Official Title:
An Interventional Study on the Association Between Diet, Cognitive Function, Stress and the Gut Microbiota in Healthy Volunteers.
Actual Study Start Date :
Jul 14, 2022
Anticipated Primary Completion Date :
Jul 1, 2026
Anticipated Study Completion Date :
Jul 1, 2026

Arms and Interventions

Arm Intervention/Treatment
Active Comparator: Control

Participants will recieve dietary education based on the healthy eating guidleines provided by the Health Service Executive (HSE).

Other: Control
Participants will recieve dietary education based on the Irish healthy food pyramid.

Experimental: Fermented Foods

Fermented foods diet (4-6 portions/day)

Other: Fermented Foods
Participants will recieve dietary education to include 4 to 6 portions of fermented foods to their normal diet.

Experimental: High Fibre

High fibre diet (24-35 grams/day)

Other: High Fibre
Participants will recieve dietary education to increase their fibre intake to 24-35g/day in their normal diet.

Experimental: Combined Diet

Combined diet high in fibre and fermented foods (fibre aim 24-35 grams/day, fermented foods aim 4-6 portions/day)

Other: Combined Diet
Participants will recieve dietary education to increase their fibre intake to 25-30g/day and include 3 to 4 portions of fermented foods to their normal diet.

Outcome Measures

Primary Outcome Measures

  1. Trait stress/mood: self-report [Change from baseline at 8 weeks]

    self-report questionnaires

  2. Trait stress/mood: hypothalamic-pituitary-adrenal axis activity [Change from baseline at 8 weeks]

    Cortisol from saliva samples

  3. Responses to acute stress: self-report [Change from baseline at 8 weeks]

    Self-report questionnaires

  4. Responses to acute stress: sympathetic-adrenal-medullary pathway activity [Change from baseline at 8 weeks]

    Galvanic skin response taken from the skin on the hand

  5. Responses to acute stress: hypothalamic-pituitary-adrenal axis activity [Change from baseline at 8 weeks]

    Cortisol from saliva samples

Secondary Outcome Measures

  1. Cognitive performance: working memory [Change from baseline at 8 weeks]

    Spatial Working Memory

  2. Cognitive performance: episodic memory [Change from baseline at 8 weeks]

    Modified Rey Auditory Verbal Learning Test (ModRey)

  3. Cognitive performance: decision making [Change from baseline at 8 weeks]

    Iowa Gambling Task

  4. Cognitive performance: emotional inhibition [Change from baseline at 8 weeks]

    Emotional Stroop

  5. Cognitive performance: sustained attention [Change from baseline at 8 weeks]

    Rapid Visual Information Processing

  6. Cognitive performance: visual pattern recognition memory [Change from baseline at 8 weeks]

    Pattern Recognition Memory

  7. Cognitive performance: cognitive flexibility [Change from baseline at 8 weeks]

    Intra-Extra Dimensional Set Shifting

  8. Cognitive performance: social cognition [Change from baseline at 8 weeks]

    Emotion Recognition Task

  9. Cognitive performance: affective perceptual bias [Change from baseline at 8 weeks]

    Emotional Bias Task

  10. Microbiota composition and function [Change from baseline at 8 weeks]

    Shotgun metagenomics of fecal samples

  11. Microbial and host metabolomics [Change from baseline at 8 weeks]

    Untargeted metabolomics analysis

  12. Inflammation [Change from baseline at 8 weeks]

    Inflammatory markers in lipopolysaccharide stimulated and unstimulated bloods

Eligibility Criteria


Ages Eligible for Study:
18 Years to 50 Years
Sexes Eligible for Study:
Accepts Healthy Volunteers:
Inclusion Criteria:
  • Be able to give written informed consent.

  • Be between 18 and 50 years of age.

  • Have a body mass index (BMI) between 18.5-29.9 Kg/m2.

  • Be in generally good health as determined by the investigator.

Exclusion Criteria:
  • Are less than 18 and greater than 50 years of age.

  • Have a BMI below 18.5 or above 29.9 Kg/m2.

  • Have a significant acute or chronic coexisting illness [cardiovascular, gastrointestinal (GI) [to include functional GI disorders, inflammatory bowel disease, coeliac disease, lactose intolerance, food allergies], immunological, psychiatric [to include formal or as determined by MINI Psychiatric interview, diagnosis of current major depression, anxiety disorder, bipolar spectrum disorder, schizophrenia, other DSM-IV Axis I disorder], neurodevelopmental disorders, immunological, metabolic disorders [to include type I or II diabetes], or any condition which contraindicates, in the investigators judgement, entry to the study,

  • Have a condition or taking a 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; all psychoactive medications [to include anxiolytics, antipsychotics, antidepressants, anticonvulsants, centrally acting corticosteroids, and opioid pain relievers), laxatives, enemas, antibiotics, anti-coagulants, over-the counter non-steroidal anti-inflammatories (NSAIDS). Subjects should have a wash-out period of 4 weeks.

  • Current prebiotic or probiotic supplement use (a wash-out period of 4 weeks after cessation will allow entry to the study).

  • Females who are peri-menopausal, menopausal or post-menopausal.

  • Females who are pregnant or planning a pregnancy, or lactating.

  • Participants who are not fluent in English.

  • Are colour blind.

  • Have dyslexia or dyscalculia.

  • Are a current habitual daily smoker.

  • 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.

  • Subjects receiving treatment involving experimental drugs. If the subject has been in a recent experimental trial, these must have been completed not less than 30 days prior to this study.

  • Have a malignant disease or any concomitant end-stage organ disease.

  • Have completed a study in our laboratory in the past 4 years.

Contacts and Locations


Site City State Country Postal Code
1 APC Microbiome Ireland Cork Ireland T12YT20

Sponsors and Collaborators

  • University College Cork


  • Principal Investigator: John Cryan, PhD, APC Microbiome Ireland

Study Documents (Full-Text)

None provided.

More Information


None provided.
Responsible Party:
University College Cork
ClinicalTrials.gov Identifier:
Other Study ID Numbers:
  • APC 150b
First Posted:
Jul 5, 2023
Last Update Posted:
Jul 5, 2023
Last Verified:
Jun 1, 2023
Studies a U.S. FDA-regulated Drug Product:
Studies a U.S. FDA-regulated Device Product:
Keywords provided by University College Cork

Study Results

No Results Posted as of Jul 5, 2023