The Relationship Between Diet, Cognition, Stress, and the Gut Microbiota

Study Overview
=================
Brief Summary
-----------------
This study aims to investigate the relationship between diet and the microbiota-gut-brain axis.

Detailed Description
-----------------
Dietary fibre is well-known for its many health benefits, including the support of gastrointestinal, metabolic, and mental health. Although studies investigating whole dietary patterns in relation to cognition have demonstrated that diet quality and a healthy dietary pattern are associated with better cognitive performance, the role of dietary fibre in this regard is understudied. It is now understood that the gut microbiota (trillions of microbes inhabiting the gastrointestinal tract) communicates bidirectionally with the brain to influence mental health and cognition. Importantly, dietary fibre has been shown to positively affect the microbiota composition. The aim of this study is to understand the effects of dietary fibre on the microbiota-gut-brain axis. Using a cross-sectional design, habitual low fibre (<=18 grams/day, n=200), moderate fibre (18.1-24.9 grams/day, n=75), and high fibre (=>25 g/day, n=75) consumers will be compared at baseline on measures of cognition, responses to acute and chronic stress, and biological markers of the microbiota-gut-brain axis. The investigators hypothesize that participants with higher dietary fibre intake at baseline will perform better in the cognitive tasks compared to individuals with low fibre intake, and that this difference can, in part, be mediated by the gut microbiota.

Official Title
-----------------
The Relationship Between Diet, Cognition, Stress, and the Gut Microbiota: A Cross-sectional Study in Healthy Adults

Conditions
-----------------
Healthy

Intervention / Treatment
-----------------
* Other: Dietary fibre


Participation Criteria
=================
Eligibility Criteria
-----------------
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.

Ages Eligible for Study
-----------------
Minimum Age: 18 Years
Maximum Age: 50 Years

Sexes Eligible for Study
-----------------
All

Study Plan
=================
How is the study designed?
-----------------

Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Low fibre consumers<br>Healthy adults consuming less than or equal to 18 grams of fibre per day. | Other: Dietary fibre<br>* Habitual dietary consumption from a variety of foods will be assessed using 7-day food logs entered by the participant and assessed for accuracy by a dietitian.<br>|
| Moderate fibre consumers<br>Healthy adults consuming between 18.1-24.9 grams of fibre per day. | Other: Dietary fibre<br>* Habitual dietary consumption from a variety of foods will be assessed using 7-day food logs entered by the participant and assessed for accuracy by a dietitian.<br>|
| High fibre consumers<br>Healthy adults consuming greater than or equal to 25 grams of fibre per day. | Other: Dietary fibre<br>* Habitual dietary consumption from a variety of foods will be assessed using 7-day food logs entered by the participant and assessed for accuracy by a dietitian.<br>|

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Trait stress/mood: self-report | Self-report questionnaires | Compared at baseline | 
| Trait stress/mood: hypothalamic-pituitary-adrenal axis activity | Cortisol from saliva samples | Compared at baseline | 
| Responses to acute stress: self-report | Self-report questionnaires | Compared at baseline | 
| Responses to acute stress: hypothalamic-pituitary-adrenal axis activity | Cortisol from saliva samples | Compared at baseline | 
| Responses to acute stress: sympathetic-adrenal-medullary pathway activity | Galvanic skin response taken from the skin on the hand | Compared at baseline | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cognitive performance: working memory | Spatial Working Memory | Compared at baseline | 
| Cognitive performance: episodic memory | Modified Rey Auditory Verbal Learning Test (ModRey) | Compared at baseline | 
| Cognitive performance: decision making | Iowa Gambling Task | Compared at baseline | 
| Cognitive performance: emotional inhibition | Emotional stroop | Compared at baseline | 
| Cognitive performance: sustained attention | Rapid Visual Information Processing | Compared at baseline | 
| Cognitive performance: visual pattern recognition memory | Pattern Recognition Memory | Compared at baseline | 
| Cognitive performance: cognitive flexibility | Intra-Extra Dimensional Set Shifting | Compared at baseline | 
| Cognitive performance: social cognition | Emotion Recognition Task | Compared at baseline | 
| Cognitive performance: affective perceptual bias | Emotional Bias Task | Compared at baseline | 
| Microbiota composition and function | Shotgun metagenomics of fecal samples | Compared at baseline | 
| Microbial and host metabolites | Untargeted metabolomics analysis in fecal and urine samples | Compared at baseline | 
| Inflammation | Inflammatory markers in lipopolysaccharide stimulated and unstimulated bloods | Compared at baseline | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
Microbiota-gut-brain axis, Diet, Cognition, Stress, Dietary fibre