Crohn's Disease

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed 27 August 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.⁸ This page already says the important thing and it is worth repeating here. Crohn's disease is progressive and transmural, and the damage it does between flares is structural and permanent: strictures, fistulas, abscesses, and eventually surgery. Modern treatment aims at mucosal healing precisely because symptom control alone does not prevent that. Nothing on this page is a substitute for that treatment, and delaying effective therapy in moderate-to-severe disease in order to try diet first is the one decision here with lasting consequences. Nutrition earns its place alongside treatment, where it is genuinely important: correcting the deficiencies this disease causes, maintaining weight, supporting healing after surgery, and in children inducing remission outright. One practical caution: if you have a known stricture, the usual advice to eat more fiber does not apply to you, and a high-residue meal can precipitate an obstruction.

1. On disease behaviour: Crohn's disease is transmural and can affect any part of the gastrointestinal tract in discontinuous "skip" lesions, which distinguishes it from ulcerative colitis. Transmural inflammation is what produces strictures, fistulas and abscesses, and these accumulate over years. The terminal ileum and right colon are the commonest sites. ↩
2. On smoking. Smoking is the most important modifiable risk factor in Crohn's disease. It increases the risk of developing it, of relapse, of needing surgery, and of recurrence after surgery; a systematic review of risk factors for post-operative recurrence found active smoking at and after surgery associated with recurrence across multiple studies, PubMed 38887827. This is the opposite of the relationship seen in ulcerative colitis, which causes real confusion, and it is worth being explicit: in Crohn's, stopping smoking is one of the most effective single interventions available, and it compares favourably with medication in its effect on the disease course. ↩
3. On treat-to-target: current practice aims at objective remission, meaning mucosal healing measured by endoscopy or biomarkers such as faecal calprotectin, rather than symptom control alone, because symptoms correlate poorly with inflammation and structural damage accrues silently. This is the reasoning behind not delaying effective therapy in moderate-to-severe disease. ↩
4. On nutritional consequences: terminal ileal disease or resection impairs vitamin B12 and bile acid absorption, producing B12 deficiency and bile-acid diarrhoea respectively. Iron deficiency is common from both blood loss and impaired absorption, and inflammation complicates its interpretation. Vitamin D deficiency, low bone density, and in extensive small bowel disease fat-soluble vitamin and micronutrient deficiencies are all recognised. Growth failure and delayed puberty are important considerations in children. These are the areas where nutrition is not adjunctive but central. ↩
5. On fiber and strictures. General advice to increase fiber does not apply to someone with a known stricture. High-residue food increases the bulk that must pass a narrowed segment and can precipitate obstruction. A low-residue approach is standard during flares and in stricturing disease, and fiber should be discussed with the team managing you rather than adjusted from a general recommendation. ↩
6. On dietary therapies, ranked honestly by evidence. Exclusive enteral nutrition has the strongest evidence: in children it induces remission with mucosal healing, and European guidance recommends it as first-line induction therapy in paediatric Crohn's, ahead of corticosteroids. Adherence in adults is substantially harder, which limits its use rather than its efficacy. The Crohn's Disease Exclusion Diet with partial enteral nutrition has randomized support for inducing and sustaining remission in mild-to-moderate disease, with better tolerability than EEN. The Specific Carbohydrate Diet was tested head-to-head against a Mediterranean diet in the DINE-CD trial and did not prove superior, with the Mediterranean diet preferred on practicality grounds. Low-FODMAP reduces functional symptoms in IBD but has not been shown to reduce inflammation, and it is a symptom strategy, not a disease-modifying one. Presenting these as equivalent obscures a real difference. ↩
7. On probiotics in Crohn's, including the negative trial. High-strength multi-strain preparations have genuine randomized evidence in pouchitis and in ulcerative colitis. That evidence does not transfer to Crohn's disease. Cochrane reviews have found insufficient evidence that probiotics maintain remission in Crohn's, and trials of probiotics for preventing post-operative recurrence have been disappointing. For Saccharomyces boulardii specifically, a randomized placebo-controlled trial of maintenance after remission in Crohn's found no reduction in relapse. Probiotics are retained on this page as low-risk and reasonable for general gut health, not as treatment for Crohn's. ↩ ↩
8. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic.