Crohn's disease (CD) is a chronic, incurable condition associated with inflammation in the gut lining. It causes diarrhoea, severe abdominal pain, poor nutrition and adversely affects the quality of life of sufferers. Two of the best treatments currently used in people with CD are drug injections and/or infusions (biologics), and a liquid-only diet using specialised milkshakes. However, treatment with biologics is only successful in approximately 40% of the patients, and although treatment with the liquid-only diet has a better safety and effectiveness profile, it is difficult for patients to stick to this as their sole source of nutrition for 6-8 weeks, particularly for adults. BIOPIC study aims to investigate whether replacing half of a habitual diet with specialised milkshakes will improve response to standard treatment with biologics in adults with CD.

80 adult patients with active CD who are due to start biologic injections therapy with adalimumab as part of their standard of care for the first time will be recruited for this study. Patients will be randomly allocated to replace either half of their normal diet with nutritionally complete milkshakes or to follow their usual diet for 6 weeks. The investigators will compare the proportion of patients whose symptoms and disease markers will improve between the two groups at 6 and 12 weeks, and how many of them will remain symptoms-free for up to a year following treatment. The investigators will also explore whether the half-liquid diet will influence patients' nutrition and quality of life. Last, the investigators will investigate if gut bacteria changes and their metabolites associate with patients' eating habits and their responses to treatment with biologics.

The primary aim of the BIOPIC study is to investigate if replacement of 50% of habitual food intake with a proprietary liquid diet for 6 weeks will improve remission rates at 12 weeks in adult patients with active ileocolonic CD treated with first-line biologics (TNFα antagonists, adalimumab) as their standard treatment of care. The secondary aim is to investigate if replacement of 50% of habitual food intake with a proprietary liquid diet for 6 weeks will prolong remission in adult patients with active ileocolonic CD treated with first-line biologics (TNFα antagonists) as their standard treatment of care.

Inclusion Criteria:

• Eligible participants are all adults (≥16 years old) with active CD (defined as Crohn's Disease Activity Index ≥ 150) who are due to initiate standard adalimumab (TNFα antagonist) induction treatment (160 mg day 0, 80 mg at 2 weeks and then 40 mg every 2 weeks).

Exclusion Criteria:

• Inability to provide written consent to participate in the study
• Pregnant and/or breastfeeding individuals
• Presence of stoma
• Presence of short bowel syndrome
• Previous treatment with an anti-TNFα inhibitor
• Use of any other biologic therapy or oral small molecule therapy within the last 12 weeks
• Patients currently receiving oral or intravenous steroids at a dosage >20mg/day prednisolone or >9mg budesonide
• Introduction of or change in dose of immunomodulator (azathioprine, mercaptopurine, methotrexate) within the past 8 weeks
• Use of oral antibiotics within the past 4 weeks
• CD with a major fistulising or symptomatic fibrotic stricturing phenotype
• Patients tested positive for blood-borne viruses such as HIV and Hepatitis
• Patients with untreated tuberculosis (latent or active)
• Current enrolment in other studies of an investigational product or dietary intervention
• Food allergies, which do not permit participation in the study (e.g., cow's milk allergy)

Participants will be asked to provide written consent for their anonymised data to be made available to public repositories.