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Guide · by Alexandra Lasconi

Crohn's disease and ulcerative colitis: what you can influence

Crohn's disease and ulcerative colitis are the two main forms of inflammatory bowel disease (IBD): long-term inflammation of the gut, in flares and quieter periods. Crohn's can affect any part of the digestive tract, often the end of the small intestine; ulcerative colitis affects the large intestine. Medical treatment is what brings and keeps the gut in remission. Nutrition is how you protect that remission, correct the deficiencies IBD causes, keep your muscle, and lower the risk factors you can control, for you and your children.

Your gastroenterologist leads your treatment. See a doctor promptly for blood in your stool, diarrhoea that wakes you at night, weight loss without trying, fever, or severe or constant abdominal pain. Never stop or change IBD medication on your own, even when you feel well.
01

What IBD is

Autoimmune or not? Genes or environment? An honest answer.

 02

Risk factors

What studies link to IBD, and what you can change.

 03

How to eat

In remission, in a flare, and why long elimination lists backfire.

 04

Deficiencies and tests

Iron, B12, vitamin D and more: what runs low and why.

 05

Muscle and strength

Why protein and training matter more with IBD.

01 · What IBD is, and what it is not

Is it autoimmune? IBD is often called autoimmune, but researchers describe it more precisely as immune-mediated: the immune system in the gut over-reacts to the trillions of microbes that live there, in people whose genes make them susceptible, rather than attacking one specific body tissue the way classic autoimmune diseases do. The history is interesting: in 1959, Broberger and Perlmann found antibodies in people with colitis that reacted with colon tissue, and later work showed such antibodies can cross-react with common gut bacteria such as E. coli. No single autoantibody causes IBD, and it is not passed from person to person.

Is it genetic? Partly. More than 200 regions of DNA are linked to IBD (NOD2 was the first), and having a close relative with IBD raises your risk. But genes are not destiny: IBD has risen fast in countries that recently industrialised, and children of families who move from low- to high-incidence countries take on the higher risk within a generation. Genes load the gun; diet, microbes, medicines and stress pull the trigger.

Can it be reversed? You will read online that Crohn's and colitis are "reversible". What is true and hopeful: with the right treatment many people reach deep remission, with a healed gut lining and years without symptoms, and lifestyle helps keep it there. What is not supported by evidence: that diet or supplements alone cure IBD, or that medication can be dropped once you feel better. Relapse after stopping treatment is common.

02 · Risk factors studies link to IBD

These come from large observational studies: they show links, not proof of cause, and most people with these exposures never develop IBD. They are still useful, because several are things you can change, or protect your children from.

FactorWhat studies foundWhat you can do
Ultra-processed food1 to 4 servings a day: about 1.7 times the risk; 5 or more: about 1.8 times, versus under 1 a day (116,000 adults, 21 countries).Base meals on whole foods; keep packaged snacks, processed meat and sugary drinks occasional.
Antibiotics in early lifeAnti-anaerobic antibiotics before age 1: about 5.5 times the risk of childhood IBD; the link weakens with age.Use antibiotics when truly needed, as prescribed; ask your doctor whether they are necessary.
Repeated antibiotics in adultsLinked to a higher risk of Crohn's, strongest for metronidazole and fluoroquinolones.The same: no antibiotics "just in case".
Food poisoningSalmonella or Campylobacter infection: about 3 times the risk, lasting years; other gastroenteritis about 2 times.Food safety at home and when travelling.
SmokingAbout twice the risk of Crohn's, and more flares and surgery.Stopping smoking is one of the strongest things you can do for Crohn's.
DepressionLinked to a higher risk of both Crohn's and colitis, lower in people treated with antidepressants.Mental health care is part of gut care.
A previous IBS diagnosisIBD is diagnosed far more often in people previously told they had IBS, partly because early IBD can look like IBS.If "IBS" comes with blood, weight loss or night symptoms, ask for further tests (for example faecal calprotectin).

03 · How to eat with IBD

In remission

  • A Mediterranean-style pattern: vegetables, fruit, legumes, whole grains, olive oil, fish. Guidance from the International Organization for the Study of IBD supports this.
  • Fewer ultra-processed foods, processed meat and some additives (emulsifiers such as carboxymethylcellulose and polysorbate 80, and carrageenan), which damaged the gut barrier in studies.
  • Fruit and vegetables every day if you tolerate them; cooked, peeled and blended is easier.
  • Protein at every meal and enough food overall: being underweight raises the risk of complications.

In a flare

  • Lower fibre for a short time if you have a narrowing (stricture), on your doctor's advice: soft, cooked, peeled foods.
  • Small, frequent meals and plenty of fluids, with salt if you have diarrhoea.
  • Medical nutrition works: exclusive enteral nutrition (a complete liquid formula) is first-line treatment for Crohn's in children, and the Crohn's Disease Exclusion Diet with partial formula helped induce remission in studies. Only with your IBD team.
  • Then rebuild variety as soon as the flare settles.
Why long elimination lists backfire. Most people with IBD avoid some foods, and malnutrition is common. Each removed group takes protein, fibre, calcium, iron or B vitamins with it, and a narrower diet means a less diverse microbiome. Keep a symptom diary, cut only what clearly triggers symptoms, and work with a dietitian who knows IBD.

04 · Deficiencies and blood tests

Inflammation, a damaged gut lining, surgery, medication and eating less all drain nutrients. Ask your doctor to check these regularly:

TestWhy with IBD
Full blood count, ferritin, transferrin saturationAnaemia is the most common complication outside the gut; ferritin reads falsely normal when inflammation is high, so transferrin saturation and CRP are read with it.
Vitamin B12Absorbed at the end of the small intestine, where Crohn's often sits or surgery removes it.
FolateMethotrexate and sulfasalazine lower it.
Vitamin D, calcium; bone density if on steroidsLow vitamin D is common; steroids thin bones.
Zinc and magnesiumLost with diarrhoea; low zinc slows healing.
CRP, albumin; faecal calprotectinInflammation and nutrition status; calprotectin tracks gut inflammation (your doctor orders and reads it).

05 · Muscle and strength

Muscle loss (sarcopenia) is common in IBD, even at a normal weight, and it predicts more complications and worse response to treatment. European nutrition guidelines (ESPEN) recommend about 1.2 to 1.5 g of protein per kg of bodyweight a day in active disease and about 1 g in remission. Strength training is safe in IBD and helps protect muscle and bone; start gently and build up, and pause during a severe flare.

06 · The plan

1. Treatment firstRemission with your gastroenterologist; medication as prescribed.
2. TestThe blood tests above; correct deficiencies with your doctor.
3. Build up your foodMediterranean-style, fewer ultra-processed foods, protein at every meal, at maintenance calories or above if you are underweight.
4. Protect muscle and gutStrength training 2 to 3 times a week; rebuild variety step by step with the Gut rebuild guide.

Bloating and diarrhoea even in remission? Small intestinal bacterial overgrowth is more common with Crohn's and after bowel surgery: see our SIBO guide.

Sources

  1. Bischoff SC et al. ESPEN guideline on clinical nutrition in inflammatory bowel disease. Clin Nutr (2023).
  2. Levine A et al. Dietary guidance from the International Organization for the Study of Inflammatory Bowel Diseases. Clin Gastroenterol Hepatol (2020).
  3. Narula N et al. Association of ultra-processed food intake with risk of inflammatory bowel disease: prospective cohort study (PURE). BMJ (2021).
  4. Kronman MP et al. Antibiotic exposure and IBD development among children: a population-based cohort study. Pediatrics (2012).
  5. Ungaro R et al. Antibiotics associated with increased risk of new-onset Crohn's disease but not ulcerative colitis: a meta-analysis. Am J Gastroenterol (2014).
  6. Gradel KO et al. Increased short- and long-term risk of inflammatory bowel disease after Salmonella or Campylobacter gastroenteritis. Gastroenterology (2009).
  7. Frolkis AD et al. Depression increases the risk of inflammatory bowel disease, which may be mitigated by the use of antidepressants in the treatment of depression. Gut (2019).
  8. Levine A et al. Crohn's disease exclusion diet plus partial enteral nutrition induces sustained remission in a randomized controlled trial. Gastroenterology (2019).
  9. Jostins L et al. Host–microbe interactions have shaped the genetic architecture of inflammatory bowel disease. Nature (2012).
  10. Ng SC et al. Worldwide incidence and prevalence of inflammatory bowel disease in the 21st century. Lancet (2017).
  11. Benchimol EI et al. Inflammatory bowel disease in immigrants to Canada and their children. Am J Gastroenterol (2015).
  12. Chassaing B et al. Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome. Nature (2015).

This page is nutrition coaching information, not medical advice. Your gastroenterologist diagnoses and treats IBD; talk to them before changing medication, starting supplements or following any special diet.

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