Study was suspended on September 24 because of funding constraints. At that point, approximately 50 % of the planned participants had enrolled. All data collected to date will be analyzed.

This study aims to evaluate a novel diet for adult Crohn's disease patients (The Crohn's Disease Exclusion Diet - CDED). Some of the patients in this study will receive the CDED combined with partial enteral nutrition (PEN), while the other group will receive the CDED with early introduction of dairy products, that were eliminated from the initial CDED protocol.

Crohn's disease (CD) is a chronic relapsing inflammatory bowel disease that has a significant impact on patients' quality of life and is of increased incidence worldwide. The disease aetiology is complex and not fully understood. Accumulated data indicate that environmental factors, including diet, might play a key role in the pathogenesis and inflammation, through mechanisms involving gut dysbiosis, in genetically susceptible people. Epidemiological data suggest that a Mediterranean dietary pattern is associated with decreased risk for CD, whereas a Western diet, rich in animal fat, processed foods and food additives, seems to be linked with an increased disease risk.

Exclusive Enteral Nutrition (EEN) is the only well-established dietary therapy in CD and is used as the first line therapy for the induction of remission in mild to moderate pediatric CD. Evidence according to EEN efficacy in adults is not consistent, which could partly be explained by the compliance difficulty. It is of interest, that feacal inflammation increases rapidly after food re-introduction following EEN in children. Partial enteral nutrition (PEN) has been shown to be beneficial in maintaining remission, but poor compliance due to low formula palatability and patients' fatigue remains an important barrier in the clinical practice. Moreover, PEN is inferior to EEN in inducing remission. Crohn's Disease Exclusion Diet (CDED), which eliminates specific dietary components hypothesized to induce dysbiosis, appears to be effective in inducing and maintaining remission both in pediatric and adult populations. In parallel, patients express a strong interest in ways to manage their disease through diet, so the establishment of a palatable and as flexible as possible dietary pattern, not merely for inducing remission, but also as a feasible maintenance strategy is one of the main priorities in CD research at present.

Therefore, the aim of this study is to explore the effectiveness of the CDED and PEN in both inducing and maintaining remission of CD in adults. The investigators also wish to challenge patients with an early exposure to dairy products, to assess tolerability, prospecting for the development of a more flexible dietary approach based on the CDED principles. The investigators aim to assess the intervention effect on CD activity, based on routinely used clinical indices, blood and faecal inflammatory biomarkers (CRP, FC), health-related quality of life, nutritional status and dietary intake, in patients with mildly active CD.

Inclusion Criteria:

• Participants must have an established diagnosis of CD
• Participants must have clinically active disease defined as HBI ≥ 5
• Participants must have confirmed inflammation at screening as CRP > 5 mg/L, FC >100 mg/g, or presence of inflammation on endoscopy in the 3 months before screening based on retrospective review of procedure reports by the local investigator and the clinician's assessment
• Individuals able to give informed consent and willingness to participate

Exclusion Criteria:

• Age < 18 years old
• Previous extensive bowel resection
• Reported pregnancy or lactation
• Current stoma
• Current abscess
• Clinically significant stricture
• Introduction of or change in dose of drug therapy within the past 8 weeks
• Comorbidities including diabetes or coeliac disease, or other concomitant serious comorbidity e.g. significant psychiatric, hepatic, renal, endocrine, respiratory, neurological, cardiovascular, neoplastic or other autoimmune disease
• Food allergies or intolerances, which do not permit participation in the study
• Any proven current infection such as positive stool cultures or positive tests for parasites or C. difficile. Stool tests are mandatory only if diarrhea is present.