Inclusion Criteria:  Fifty-five successive male or female patients with Functional Gastrointestinal Disorders FGID) enrolled from our Gastroenterology Group Practice (GGP) in Bern, Switzerland, classified as having either Irritable Bowel Syndrome (IBS), Functional Dyspepsia (FD) or both according to Rome 4 criteria (Drossman et al 2016; Schmulson et al. 2017) Age between 18 and 50 years Body mass index 18.5-29.9 kg/m2 European / Caucasian ethnicity Able to give informed consent in German as documented by signature  Exclusion Criteria:  Evidence of clinically significant disease, as assessed by usual clinical practice (history, blood and stool tests, imaging and endoscopy, as clinically required) and by investigator. Colonoscopy, antibiotics or probiotics within 2 weeks before or during the study. Planned dietary modifications (including polyphenol-rich fruit or vegetable smoothies, drinks or diets) or initiation of new treatments during the study period, besides the study interventions. Inability or contraindications to undergo the investigated intervention Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc.