Dietary Fiber, Microbiota and Cognitive Function in Healthy Adults

Study Overview
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Brief Summary
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Dietary fiber 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 fiber in this regard is understudied. In the last decade, the role of the microbiota (trillions of microbes inhabiting the gut) in influencing various aspects of human health, including mental health and behavior, has also become established. Importantly, dietary fiber has been shown to positively affect the microbiota composition. In this study, the role of dietary fiber in cognition through the lens of the microbiota is investigated. A two-part study including an observational (study 1) and interventional (study 2) arm has been designed. In study 1, the observational arm, 150 healthy individuals (30-60 years of age) will be recruited and grouped into high-fiber (>25 g/day, n=75) and low-fiber (<18 grams/day, n=75) consumers based on habitual dietary intake. Cognitive tasks (attention, episodic memory, decision making), psychological dimensions including impulsivity and emotional reactivity, biological samples (feces, blood, saliva, urine) and questionnaires about general health will be collected. In study 2, the interventional arm, a subgroup (n=60) of individuals from the low-fiber group will further be randomized into an 8-week randomized-controlled, parallel, single-blinded intervention to either receive a high fiber (n=30, aim 30 grams/day) or control (n=30) diet education. During the intervention period, individuals will provide repeated fecal samples in order to assess temporal microbial changes. At the end of the intervention period, individuals will undergo the same testing regarding cognitive and psychological variables and the same biological samples will be collected. The investigators hypothesize that participants with higher dietary fiber intake at baseline will perform better in the cognitive tasks compared to individuals with low fiber intake, and that this difference can, in part, be mediated by the gut microbiota. Further the investigators hypothesize that through the dietary intervention the microbiota composition will positively shift to include more beneficial microbes and that cognitive performance will improve following the intervention.

Official Title
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An Observational and Interventional Study on the Association Between Dietary Fibre and Cognitive Function in Healthy Volunteers

Conditions
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Healthy

Intervention / Treatment
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* Other: High fiber diet
* Other: Control diet


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Be able to give written informed consent. Be between 30 and 60 years of age. Be in generally good health as determined by the investigator. Exclusion Criteria: Are less than 30 and greater than 60 years of age. Have a significant acute or chronic coexisting illness [cardiovascular, gastrointestinal (GI) [to include functional GI disorders, inflammatory bowel disease, celiac 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). Participants 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 or English is not first language. Are color 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. Participants 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 the laboratory in the past 4 years.

Ages Eligible for Study
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Minimum Age: 30 Years
Maximum Age: 60 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: DIET<br>Participants will receive four individual, approximately 30-minute long dietary education sessions. The participants will receive detailed instructions (including meal plans, information on high fiber foods and serving sizes) on how to consume at least 30 grams of fiber per day. | Other: High fiber diet<br>* 30 grams of fiber per day<br>|
| Placebo Comparator: CONTROL<br>No diet education. Group will spend same amount of time with study dietitian, but discussion is limited to review of current eating habits and minimal input on eating habits with referencing the standard food pyramid. | Other: Control diet<br>* No diet education and change in diet<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cognitive performance - Attention | Assessment of attention using the Paced Auditory Serial Addition Test (PASAT) | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Cognitive performance - Episodic memory | Assessment of episodic memory using the Modified Rey Auditory Verbal Learning Test (ModRey) | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Cognitive performance - Risky decision making | Assessment of risky decision making using the Cambridge Gambling Task (CGT) | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Cognitive performance - Affective decision making | Assessment of affective decision making using the Iowa Gambling Task (IGT). | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Microbiota composition and function | Shotgun sequencing of fecal samples | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Blood inflammatory profile | Cytokine and chemokine levels (e.g., TNFalpha, IL-10, IL-6) will be measured in lipopolysaccharide stimulated and unstimulated bloods | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Salivary cortisol concentrations | Morning cortisol awakening response | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Stress assessment | Perceived Stress Scale (range 0 to 40 with higher scores indicating higher perceived stress) | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Anxiety assessment | State Trait Anxiety Inventory (range 20-80 with higher scores indicating higher anxiety) | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Emotion sensitivity, intensity, and persistence | Emotion Reactivity Scale (range 0-84 with higher scores indicating higher dysfunctional emotional reactivity) | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 
| Impulsivity-related traits | UPPS-P Impulsive Behavior Scale (range 59-236 with higher scores indicating higher dysfunctional impulsivity | Differences between groups at baseline and changes after 8-week of diet intervention in active group | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Microbiota, Dietary fiber, Cognition, Diet, Microbiota-Gut-Brain Axis