Crohn’s disease and ulcerative colitis (UC) are two types of inflammatory bowel disease (IBD). Neither of these conditions can be cured, but proper disease management can help reduce symptom burden and increase quality of life. 

Crohn’s Disease

Crohn’s disease is a chronic condition that causes inflammation and irritation in the digestive tract, which extends from the mouth to the anus; it can affect any part of the digestive tract, but most commonly impacts the small and large intestines.^1–3 Inflammation can be continuous or segmented, having sections of normal intestine between sections of diseased intestine.^3,4 Additionally, the entire thickness of the bowel wall can be impacted, rather than just the intestinal lining.³ In Crohn’s disease, bacteria in the digestive tract are mistaken for foreign invaders, and an immune response occurs, which causes inflammation. This inflammation does not subside, thus leading to Crohn’s disease.⁵ 

This disease affects both sexes equally and is most often diagnosed between the ages of 20 and 30 years.^1,3 There is no known cause of Crohn’s disease, but various risk factors have been identified. These include family history of IBD, smoking, being of White or Ashkenazi Jewish descent, and having an autoimmune disease.^2–5 Diet, stress,^1,5 and nonsteroidal anti-inflammatory drug (NSAID) use⁴ do not cause Crohn’s disease, but they can worsen it.

There are several types of Crohn’s disease: 

Ileocolitis: The most common type, with inflammation occurring in the ileum (end of the small intestine) and colon (longest part of the large intestine).

Ileitis: Inflammation occurs in the ileum.

Gastroduodenal Crohn’s disease: Inflammation occurs in the stomach and duodenum (beginning of the small intestine).

Jejunoileitis: Patchy inflammation occurs in the jejunum (second portion of the small intestine).^2,3

Many individuals with Crohn’s disease experience symptom flare-ups and remission, and symptoms can range from mild to severe.^1,4 Diarrhea, abdominal pain and cramping, weight loss, reduced appetite, fever, fatigue, anemia, and abnormal skin tags/skin changes are common symptoms. Crohn’s disease can also contribute to several complications, such as ulcers, bowel obstruction, malnutrition, fistulas (often near/around the anus), abscesses, anal fissures, and colon cancer.^1,2,4 Bowel obstruction can occur as the result of a stricture, which is when parts of the bowel become narrow.⁴

Ulcerative Colitis

UC causes inflammation and ulcers in the innermost lining of the colon and rectum.^3,6 Unlike Crohn’s disease, UC is restricted to the large intestine, does not affect the entire thickness of the bowel wall, and involves uniform, continuous inflammation.³ Although the cause of UC is unknown, researchers believe that an overactive immune response, wherein the immune system erroneously attacks cells in the digestive tract, plays a role in UC development.^6,7 

UC affects both sexes equally.⁶ Onset typically occurs between the ages of 15 and 30 years and 55 and 70 years.³ Being of Jewish descent and having a close relative with IBD are risk factors for UC.^6,7 

There are various types of UC:

Ulcerative proctitis: Inflammation is limited to the rectum, often affecting less than six inches, and is not correlated with an increased risk of cancer. Rectal bleeding might be the only symptom.

Left-sided colitis: Inflammation spans the rectum to the splenic flexure.

Proctosigmoiditis: Inflammation spans the rectum to the sigmoid colon.

Pancolitis/extensive colitis: Inflammation affects the entire colon.^6,8

As with Crohn’s disease, individuals with UC experience bouts of remission and disease flares, and symptoms range from mild to severe. Symptoms of UC include diarrhea, rectal bleeding, bloody stool, abdominal pain and cramping, urgent bowel movements, inability to defecate despite urgency, weight loss, fatigue, fever, nausea, and, in children, delayed growth.^6,7,9 Although not a cause of UC, NSAID use can worsen UC symptoms.¹⁰ Complications can include rapid swelling of the colon (toxic megacolon); dehydration; perforation of the colon; osteoporosis; inflammation of eyes, joints, and skin; and increased risk of colon cancer.^6,7

Treatment

Various medications can help in the management of Crohn’s disease and UC. Aminosalicylates can help reduce inflammation and are typically prescribed to patients with mild-to-moderate symptoms. Corticosteroids can be prescribed for short-term use in patients with moderate-to-severe symptoms to reduce inflammation and lessen immune system activity.^10,11 Immunomodulators can also reduce immune system activity, but they can take several weeks to three months to take effect.¹¹ Biologics target specific proteins created by the immune system to decrease inflammation.^10,11 Physicians might also prescribe antibiotics and/or antidiarrheal drugs to combat the complications of Crohn’s disease and UC.^2,10,11 

Individuals with severe Crohn’s disease can undergo bowel rest, which constitutes only consuming certain liquids through drinking, a feeding tube, or an intravenous (IV) tube for days to weeks to allow the intestines to rest.^1,11 

In some cases of Crohn’s disease, surgery to remove part of the digestive tract might be necessary to improve symptoms and treat complications, such as fistulas, life-threatening bleeding, intestinal obstructions, and perforations.^1,2,11 Likewise, individuals with UC might require surgery to remove the colon and rectum if they are unresponsive to other treatments, experience life-threatening complications (e.g., bleeding, perforation, toxic megacolon), have precancerous lesions, or have colorectal cancer.^7,10

Diet does not cause Crohn’s disease or UC, but it can affect the risk of developing either disease. For instance, consumption of dietary fiber and fruits has been associated with a decreased risk of Crohn’s disease, and high vegetable consumption has been associated with a decreased risk of UC. High intake of animal proteins, refined/processed carbohydrates, and sweetened beverages has been associated with an increased risk of IBD.¹² Processed foods and artificial sweeteners might contribute to inflammation, but further research is needed to elucidate their role in IBD.^13,14

For individuals with Crohn’s disease or UC, dietary changes, in conjunction with other therapies, could potentially aid in mitigating symptoms. Avoiding trigger foods can be beneficial for some patients. Trigger foods are associated with a worsening of symptoms, though they do not directly cause inflammation.¹³ Trigger foods vary based on the individual, but common ones include high-fiber foods, high-lactose foods, high-sugar foods and foods with added sugar, high-fat/greasy foods, spicy foods, alcohol, and carbonated beverages.^7,13 

In 2020, the International Organization for the Study of Inflammatory Bowel Diseases (IOIBD) released dietary recommendations for individuals with Crohn’s disease and UC.¹⁵ For those with Crohn’s disease, increased consumption of fruits and vegetables is recommended, although individuals with stricture should decrease insoluble fiber intake. It is also recommended to reduce the intake of saturated fats. For individuals with UC, increased intake of omega-3 fatty acids via fish, as opposed to dietary supplements, is recommended. Consumption of red/processed meats and myristic acid, which is found in palm oil, coconut oil, and dairy fats, should be reduced. In both Crohn’s disease and UC, trans fats should be avoided, and it might be advisable to limit maltodextrin, artificial sweetener, carboxymethylcellulos, and polysorbate-80 (the latter two being emulsifiers/thickeners) intake and decrease consumption of processed foods that contain carrageenan, titanium dioxide, and sulfites. There are no recommendations on specific diets due to the lack of randomized clinical trials at the time of publication.¹⁵

Below is a brief overview of several diets that are commonly recommended for individuals with IBD. Please note that the certainty of clinical evidence supporting the use of any of these diets is low,¹⁶ and no diet has been shown to prevent or control IBD, aside from enteral nutrition.¹⁷ Consult with your physician or registered dietitian before beginning a new diet.

Exclusive enteral nutrition (EEN). All calories are received through a nutritional liquid formula, and all other food and drinks, besides water, are excluded from the diet.^14,17 EEN is used as first-line therapy to induce remission in children with new-onset, mild-to-moderate Crohn’s disease, with a reported remission rate of about 80 percent.¹⁸ Following an EEN diet prior to surgery is associated with peri- and postoperative benefits, such as reduced time in surgery, reduced rate of complications, and decrease of systemic inflammation.^14,17

Low-Fermentable, Oligosaccharides, Disaccharides, Monosaccharides, and Polyol (FODMAP) diet. Intake of foods containing certain short-chain carbohydrates that might be poorly absorbed by the small intestine is eliminated. Then, foods are slowly reintroduced in order to identify foods that cause symptoms, such as bloating, cramping, and diarrhea. The elimination portion of the diet should last from two to six weeks.¹⁹ A low-FODMAP diet might provide symptom relief, but its impact on IBD pathology and inflammation is unknown.^14,17 

Crohn’s Disease Exclusive Diet (CDED). Foods that might have adverse effects on the gut microbiome, inflammation, and intestinal functions are cut from the diet. Excluded foods include red meat, animal fat, wheat, dairy, processed foods, and additives. It is recommended to undertake this diet with partial enteral nutrition to ensure sufficient energy, nutrient, and protein intake. CDED typically has three phases to gradually reintroduce various foods to the diet.¹⁷ CDED might help some patients achieve remission.^17,18

Specific Carbohydrate Diet (SCD). In this diet, intake of grains, starchy vegetables, refined and processed foods, dairy, soy, and sucrose is eliminated.^14,17 The only carbohydrate foods allowed are monosaccharides, which includes fruits and honey.¹² SCD might cause weight loss and inadequate intake of vitamin D, vitamin E, B vitamins, and calcium.¹⁷ Research has shown that SCD and the Mediterranean diet (information below) improved inflammation, symptoms, and quality of life in patients with mild-to-moderate Crohn’s disease,^14,17 but neither diet has been shown to be superior to a standard diet.¹⁶

Mediterranean diet. This diet involves high consumption of fruits, vegetables, unsaturated fats, and nuts, and moderate consumption of fish and dairy. Intake of meat, saturated fats, and sweetened foods is limited.¹⁴ Research has suggested that adhering to a Mediterranean diet can reduce disease activity¹⁴ and improve inflammatory markers, nutritional status, and quality of life in patients with Crohn’s disease and UC.¹⁷

Bottom Line

Crohn’s disease and UC are complex gastrointestinal diseases. Although there is no cure, these diseases can be successfully managed through various interventions.

Sources

1. MedlinePlus. Crohn’s disease. Updated 18 Oct 2023. https://medlineplus.gov/crohnsdisease.html#:~:text=What%20is%20Crohn%27s%20disease%3F,beginning%20of%20your%20large%20intestine. Accessed 7 Nov 2023.
2. Cleveland Clinic. Crohn’s disease. Reviewed 28 May 2020. https://my.clevelandclinic.org/health/diseases/9357-crohns-disease. Accessed 7 Nov 2023.
3. Crohn’s and Colitis Foundation. Overview of Crohn’s disease. https://www.crohnscolitisfoundation.org/what-is-crohns-disease/overview. Accessed 7 Nov 2023.
4. Mayo Clinic Staff. Crohn’s disease – symptoms and causes. Mayo Clinic. 6 Aug 2022. https://www.mayoclinic.org/diseases-conditions/crohns-disease/symptoms-causes/syc-20353304. Accessed 7 Nov 2023.
5. Crohn’s and Colitis Foundation. Causes of Crohn’s disease. https://www.crohnscolitisfoundation.org/what-is-crohns-disease/causes. Accessed 7 Nov 2023.
6. Mayo Clinic Staff. Ulcerative colitis – symptoms and causes. 16 Sep 2022. https://www.mayoclinic.org/diseases-conditions/ulcerative-colitis/symptoms-causes/syc-20353326. Accessed 7 Nov 2023. 
7. Cleveland Clinic. Ulcerative colitis. Reviewed 23 Apr 2020. https://my.clevelandclinic.org/health/diseases/10351-ulcerative-colitis#symptoms-and-causes. Accessed 7 Nov 2023.
8. Crohn’s and Colitis Foundation. Types of ulcerative colitis. https://www.crohnscolitisfoundation.org/what-is-ulcerative-colitis/types-of-ulcerative-colitis. Accessed 7 Nov 2023. 
9. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms and causes of ulcerative colitis. Reviewed Sep 2020. https://www.niddk.nih.gov/health-information/digestive-diseases/ulcerative-colitis/symptoms-causes. Accessed 7 Nov 2023.
10. National Institute of Diabetes and Digestive and Kidney Diseases. Treatment for ulcerative colitis. Reviewed Sep 2020. https://www.niddk.nih.gov/health-information/digestive-diseases/ulcerative-colitis/treatment. Accessed 7 Nov 2023.
11. National Institute of Diabetes and Digestive and Kidney Diseases. Treatment for Crohn’s disease. Reviewed Sep 2017. https://www.niddk.nih.gov/health-information/digestive-diseases/crohns-disease/treatment. Accessed 7 Nov 2023.
12. Reddavide R, Rotolo O, Caruso MG, et al. The role of diet in the prevention and treatment of inflammatory bowel diseases. Acta Biomed. 2018;89(9-S):60–75.
13. Crohn’s and Colitis Foundation. What should I eat? https://www.crohnscolitisfoundation.org/diet-and-nutrition/what-should-i-eat. Accessed 7 Nov 2023.
14. Gubatan J, Kulkarni CV, Talamantes SM, et al. Dietary exposures and interventions in inflammatory bowel disease: current evidence and emerging concepts. Nutrients. 2023;15(3):579.
15. Levine A, Rhodes JM, Lindsay JO, et al. Dietary guidance from the International Organization for the Study of Inflammatory Bowel Diseases. Clin Gastroenterol Hepatol. 2020;18(6):1381–1392.
16. Limketkai BN, Godoy-Brewer G, Parian AM, et al. Dietary interventions for the treatment of inflammatory bowel diseases: an updated systematic review and meta-analysis. Clin Gastroenterol Hepatol. 2023;21(10):2508–2525.e10. 
17. Crohn’s and Colitis Foundation. Special IBD diets. https://www.crohnscolitisfoundation.org/diet-and-nutrition/special-ibd-diets. Accessed 8 Nov 2023.
18. Więcek M, Panufnik P, Pomorska K, et al. Diet as therapeutic intervention in Crohn’s disease. Prz Gastroenterol. 2022;17(2):96–102. 
19. Johns Hopkins Medicine. FODMAP diet: what you need to know. https://www.hopkinsmedicine.org/health/wellness-and-prevention/fodmap-diet-what-you-need-to-know. Accessed 8 Nov 2023.