This study will evaluate if suppelementation of the diet with riboflavin in Crohn's disease patients will result in an increase in the amount of F. prausnitzii.

Rationale Recent studies show that in patients with Inflammatory Bowel Disease (IBD) a dysbiosis exists in the composition of the intestinal microbiota. In particular, the potentially pathogenic bacterium Escherichia coli (E. coli) is often more abundant in the bowel of IBD patients, and the anaerobic commensal Faecalibacterium prausnitzii (F. prausnitzii) is often reduced. This last mentioned bacteria is known to be abundant in the intestine of healthy individuals. It is known to produce butyrate, which stimulates the intestinal epithelium, and to secrete anti-inflammatory substances.

Riboflavin - also known as vitamin B2 - is required for a wide variety of cellular processes and has an important role in maintaining health in humans. In a pilot intervention with healthy volunteers it is shown that a riboflavin supplement increases the number of F. prausnitzii and results in a higher production of butyrate. In Crohn's disease patients, it is known that the amount of F. prausnitzii in the intestine is generally low. Furthermore, it is known that there is an association between the number of F. prausnitzii bacteria and the length of disease in remission.

This study will evaluate if supplementation of the diet with riboflavin in Crohn's disease patients will result in a similar increase in the amount of F. prausnitzii as in healthy volunteers. In this patient group, an increase in the number of F. prausnitzii bacteria in the bowel may result in a more favourable disease course. This will be assessed with faeces calprotectin and two questionnaires. Additionally the investigators will assess if there is any modulation by riboflavin on the other intestinal bacteria, short chain fatty acids (SCFAs) (such as butyrate), and the pH of the faeces. Finally, the effect of the riboflavin on the permeability of the gut will be evaluated with a Chroom-EDTA test, and a number of different biomarkers of permeability.

Hypothesis The hypothesis is that in Crohn's disease patients, supplementation of the diet with riboflavin results in an increase in the amount of F. prausnitzii, changes in microbial composition, increased fatty acid production, an increase in pH and a reduction of intestinal permeability. These changes might result in a more favourable disease course with less exacerbations.

Study design Prospective clinical study.

Study population and sample size In total 84 Crohn's disease patients will be included in this study, divided into two groups. Group 1 (n=42) will consist of patients with disease in remission (quiescent disease); group 2 (n=42) will consist of patients with active disease. In this study an adaptive design will be used. First 12 patients in the disease in remission group will be analysed. The methods of analysis and safety aspects will be taken into account.

Intervention Supplementation of the normal diet with 1 capsule of 100 mg riboflavin (vitamin B2) during three weeks.

Inclusion Criteria:

• Crohn's disease patients
• Age 18-65 years
• Concomitant medication for Crohn's disease is allowed in all groups

Exclusion Criteria:

• Swallowing disorders
• Pregnancy and lactation
• Use of antibiotic drugs, probiotics (i.e.Yakult, Vifit, Activia etc) or specific prebiotic supplements in the 3 weeks prior to the riboflavin intervention
• Use of Methotrexate drugs
• Colonoscopy and colon cleansing in last 3 months
• Use of a vitamin B2 supplement, or multivitamin complexes containing vitamin B (i.e. vitamin B-complex) in the 3 weeks prior to the riboflavin intervention
• Severe Crohn's disease (HBI > 12)

6 weeks

No adverse events observed in this study