Brain Responses to Short-Chain Fatty Acid Intervention

Brain HDAC expression will be quantified using the PET radiotracer [11C]Martinostat before and after the intervention

Brain response (brain oxygenation level-dependent signals) to a fMRI-adapted stress task will be measured before and after intervention

Relative quantification of brain metabolites (mmol/L) using 1H-Magnetic Resonance Spectroscopy before and after intervention

Quantification of serum SCFA (μM) before and after intervention

Biological stress sensitivity is measured by quantifying cortisol levels (ng/ml) from multiple saliva samples taken before, during, and after a stress task performed during the pre-intervention and post-intervention visit

Quantification of inflammatory cytokines (pg/ml) before and after intervention

Quantification of hs-C-reactive protein levels (ng/ml) before and after intervention

Assessing heart rate variability (ms) with ECG before and after intervention

Assessing blood pressure (systolic/diastolic mmHg) with a blood pressure monitor before and after intervention

Assessing heartbeat (bpm) with a blood pressure monitor before and after intervention

Psychological stress sensitivity is measured through stress reports of the participants using the visual analogue scale (VAS). VAS scorings are taken before, during, and after a stress task performed during the pre-intervention and post-intervention visit.

Assessing gut microbiota profile before and after intervention

Assessing ratings on PSS. PSS scores range between 0-40 with higher scores indicating worse outcome

Assessing ratings on the subscales of GSRS and its total score. It has 5 subscales (Reflux, Diarrhea, Constipation, Abdominal Pain, and Indigestion Syndrome). Subscale scores range from 1 to 7 and higher scores indicates a worse outcome.

Measuring the Big Five personality traits, including Extraversion, Agreeableness, Conscientiousness, Emotional Stability, and Openness.

General side effects will be assessed and recorded in a structured, validated approach using the Generic Assessment of Side Effects (GASE)54. The GASE consists of 36 items asking for most frequently reported side effects for drugs based on the FDA adverse event reporting system database from all countries. Symptoms of all body parts during the last seven days will be self-reported and rated based on severity from 0 (not present) to 3 (severe).

Assessing momentary (state) anxiety during the pre- and post-intervention visit. This inventory is part of the State-Trait Anxiety Inventory (STAI) with 20 questions specifically for state anxiety, rated on a 4-point scale. State anxiety is rated with anxiety absent and anxiety present questions. Anxiety absent questions constitute the absence of anxiety in a statement like, "I feel secure." Anxiety present questions represent the presence of anxiety in a statement like "I feel worried." The 4-point scale are as follows: 1 'not at all', 2 'somewhat', 3 'moderately so', and 4 'very much so'.

designed to assess individual differences in the habitual use of two emotion regulation strategies: cognitive reappraisal and expressive suppression

an instrument to measure the quality and patterns of sleep in adults. . It differentiates "poor" from "good" sleep by measuring seven domains: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction over the last month.

to assess the frequency with which people experience cognitive failures, such as absent-mindedness, in everyday life - slips and errors of perception, memory and motor functioning. The questionnaire has 25 items which are scored from Never (0), Very rarely (1), Occasionally (2), Quite often (3) to Very often (4). A total score as well as three subscales (Forgetfulness, Distractibility, False Triggering) can be calculated.

retrospective assessment of microstressors over one week covering both stressor occurence and perceived stressor intensity