This randomized, parallel, double-blind, placebo-controlled trial aims to determine the effects of daily administration of citrus extract over a period of 8 weeks on gastrointestinal health in patients with irritable bowel syndrome.

Inclusion Criteria:

• Patients with IBS
• Calprotectin levels 15-150 µg/g feces
• Age 18-70 years
• BMI < 35 kg/m2

Exclusion Criteria:

• Comorbidities that may influence gut microbiota composition or which might limit participation in or completion of the study protocol (to be decided by the principle investigator)
• Abdominal surgery interfering with gastrointestinal function (to be decided by the principle investigator)
• Use of immunosuppressive drugs within 3 months before study period
• Use of other medication interfering with endpoints
• Changes in medication that may significantly affect the study outcome according to the investigator's judgment within 1 month prior to the study
• Changes in clinical activity scores within 3 weeks prior to the study
• Administration of investigational drugs or participation in any scientific intervention study which may interfere with this study (to be decided by the principle investigator) in the 180 days prior to the study
• Use of dietary supplements containing antioxidants, minerals and vitamins
• Excessive intake of foods with a high polyphenol concentration
• Use of antibiotics within 3 months prior to the start of study
• Use of pre-or probiotics within 1 month prior to the study
• Use of oral corticosteroids within 1 month prior to the study
• Blood donation within 1 month prior to the study
• Known pregnancy or lactation.
• Excessive drinking (>20 alcoholic consumptions per week)
• History of any side effects towards the intake of flavonoids or citrus fruits