Crohn’s Disease and Ulcerative Colitis: Effects on Digestion & Diet

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The real work of digestion goes on in the small intestine, which lies just beyond the stomach. In the small intestine, digestive juices from both the liver (termed bile) and the pancreas mix with food. This mixing is powered by the churning action of the intestinal muscle wall. After digested food is broken down into small molecules, it is absorbed through the surface of the small intestine and distributed to the rest of the body by the blood stream. Watery food residue and secretions that are not digested in the small intestine pass on into the large intestine (the colon). The colon reabsorbs much of the water added to food in the small intestine. This is a kind of water conservation or recycling mechanism.

Solid, undigested food residue is then passed from the large intestine as a bowel movement.

When the small intestine is inflamed—as it often is with Crohn’s disease—the intestine becomes less able to digest and absorb food nutrients fully. Such nutrients, as well as unabsorbed bile salts, can escape into the large intestine to varying degrees, depending on how extensively and how severely the small intestine has been injured by inflammation. This is one reason why people with Crohn’s disease become malnourished, in addition to just not having much appetite. Furthermore, incompletely digested foods that travel through the large intestine interfere with water conservation, even if the colon itself is not damaged. Thus, when Crohn’s disease affects the small intestine, it may cause diarrhea as well as malnutrition. Should the large intestine also be inflamed, the diarrhea is likely to be worse. In ulcerative colitis, only the colon is inflamed; the small intestine works normally. Because the inflamed colon does not recycle water properly, diarrhea can be severe.


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Dietary recommendations for people with IBD must be individualized: They depend on which disease you have and what part of your intestine is affected. Many people have food intolerances— far more than really have true food allergies. One of the more common intolerances, lactose intolerance, is the inability to digest lactose (milk sugar), which is related to genetic tendencies and to small bowel function. Elimination tests are better at diagnosing which foods must be avoided or modified than the standard allergy skin or blood testing. Many good books discuss the proper way to follow such an “elimination diet,” which involves keeping a food and symptom diary over several weeks.

About two thirds of people with small bowel Crohn’s disease develop a marked narrowing (or stricture) of the lower small intestine, the ileum. For these patients, a low-fiber with low residue diet (see below) or a special liquid diet may be beneficial in minimizing abdominal pain and other symptoms. Often, these dietary modifications are temporary; the patient follows them until the inflammation that caused the narrowing responds either to treatment or to a corrective surgery. Individual experience, sometimes with the guidance of a registered dietitian, remains the single most useful guide to selection of foods for any person with IBD.


This diet minimizes the consumption of foods that add “scrapy” residue to the stool. These include raw fruits, vegetables, and seeds, as well as nuts and corn hulls. The registered dietitian associated with your IBD treatment program can assist you in devising such a diet when appropriate.


Yes, vitally so. IBD patients, especially people with Crohn’s disease, are prone to becoming malnourished for several reasons. First, the appetite is often reduced. Second, chronic diseases tend to increase the energy (calorie) needs of the body. This is especially the case when IBD is “flaring up. ”Third, IBD, particularly

Crohn’s disease is often associated with maldigestion and malabsorption of dietary protein, fat, carbohydrates, water, and a wide variety of vitamins and minerals. Thus, much of what one eats may never truly get into the body. On the other hand, good nutrition is one of the assets the body uses to restore itself to health. Therefore, the tendency to become malnourished must be resisted. Restoration and maintenance of good nutrition is a key principle in the management of IBD.

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An appropriate diet should contain a variety of foods from all food groups. Meat, fish, poultry, and dairy products, if tolerated, are sources of protein; bread, cereal, starches, fruits, and vegetables are sources of carbohydrate; margarine and oils are sources of fat. Your physician and the registered dietitian with whom he or she is associated can help you with meal planning. Generally, if the colon is inflamed, avoiding scrappy foods such as nuts, corn hulls, and raw vegetables is advised until some healing has occurred.


Some people cannot properly digest lactose, the sugar present in milk and many milk products, regardless of whether they have IBD. This may occur because the inner surface of the small intestine lacks a digestive enzyme, called lactase. Poor lactose digestion may lead to cramps, abdominal pain, gas, diarrhea, and bloating. Because symptoms of lactose intolerance may be very similar to the symptoms of IBD, recognizing lactose intolerance may be difficult.

A simple “lactose tolerance test” can be performed to identify the problem. If there is any question, milk ingestion may be limited. Alternatively, lactase supplements may be added to many dairy products, so that they no longer cause symptoms. Your registered dietitian may assist you and/or your child with this. It is desirable to maintain intake of at least some dairy products, because they are such a good source of nutrition, in particular calcium and protein.

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No. Although some people do have allergic reactions to certain foods, neither Crohn’s disease nor ulcerative colitis is related to food allergy. People with IBD may think they are allergic to foods because they associate the symptoms of IBD with eating.


Most often, yes. Patients with inflammation only in the large intestine absorb food normally. People with Crohn’s disease may have problems with digestion if their disease involves the small intestine. The degree to which digestion is impaired depends on how much of the small intestine is diseased and whether any intestine has been removed during surgery. If only the last foot or two of the ileum is inflamed, the absorption of all nutrients except vitamin B-12 will probably be normal. If more than two or three feet of ileum is diseased, significant malabsorption of fat may occur. If the upper small intestine is also inflamed, the degree of malabsorption in Crohn’s disease is apt to be much worse, and deficiencies of many nutrients, minerals, and more vitamins are likely. Some

IBD therapies, especially the 5-ASA medications (e.g., Asacol,® Canasa,® Colazal,® Dipentum,® Pentasa® and Rowasa®), cause interference with the absorption of folate, so this vitamin, so essential in preventing cancer and birth defects, should be supplemented.


Vitamin B-12 is absorbed in the lower ileum. Therefore, persons with ileitis (Crohn’s disease that affects the ileum) may require injections of vitamin B-12, because they cannot absorb enough from their diet. If you are on a low-fiber diet, you may be receiving an inadequate supply of certain vitamins common in fruits, such as vitamin C. In the setting of chronic IBD, it is worthwhile for most persons to take a multivitamin preparation regularly. If you suffer from maldigestion or have undergone intestinal surgery, other vitamins, particularly vitamin D, may be required. Vitamin D supplementation should be in the range of 800 U/day, especially in the non-sunny areas of the country, and calcium intake should be emphasized, with calcium citrate for those older or on acid reducing medications. Steroid use and Crohn’s disease itself are linked to bone thinning and osteoporosis, so screening with bone density studies is suggested for those at risk.

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In most IBD patients, there is no obvious lack of minerals. However, calcium, phosphorus, and magnesium supplements may prove necessary in people who have extensive small intestinal disease or who have had substantial lengths of intestine removed through surgery. Iron therapy is helpful to correct anemia. Oral iron turns the stools black, which can sometimes simulate intestinal bleeding.


Yes. In a condition with chronic diarrhea, there may be a risk of dehydration. If fluid intake does not keep up with diarrhea, kidney function may be affected. Patients with Crohn’s and other diarrheal diseases have an increased incidence of kidney stones, which is related to this problem. Furthermore, dehydration and salt loss create a feeling of weakness. For these reasons, people with IBD should consume ample fluids, especially in warm weather when skin losses of salt and water may be high.


In young people with IBD whose IBD began before puberty, growth may be retarded. Poor food intake may contribute to poor growth. Thus, good nutritional habits and adequate caloric intake are very important. Control of the disease with drugs or, less often, surgical removal of a particularly diseased region of intestine, is most successful when appropriate dietary intake is maintained.


Because IBD, especially Crohn’s disease, may improve with nutritional support, enteral nutrition (a nutrient-rich liquid formula) or tube feeding may be necessary. Due to its taste, enteral nutrition is given overnight through a tube, most commonly from the nose to the stomach. Patients are taught to pass a tube each night, so that they can receive nutrition while sleeping. In the morning, they remove the tube and go about their normal activity. In this way, patients receive all the nutrition they need and are free to eat normally—or not—throughout the day. Enteral feedings can also be given through a gastrostomy tube (G-tube). This is a tube located on the abdominal wall that goes directly into the stomach. The feedings are most commonly given overnight, but they can also be given intermittently throughout the day Parenteral nutrition (nutrition delivered through a catheter placed into a large blood vessel, usually one in the chest) is rarely needed. Parenteral nutrition has more complications than enteral nutrition and does not nourish the gastrointestinal tract itself.


Eating to help the gut heal itself is one of the new concepts, and numerous experimental studies are being conducted in this area.  Probiotics are just beginning to be appreciated as a therapeutic aid in IBD. These are “good” bacteria that restore balance to the enteric microflora—bacteria that live in everybody’s intestine. Lactobacillus preparations and live-culture yogurt can be very helpful in aiding recovery of the intestine. There is much work being done in the use of diet and supplements to aid in the healing of IBD and much more to be learned.

In summary, while there is no evidence that diet and nutrition play a role in causing IBD, maintaining a well-balanced diet that is rich in nutrients can help you to live a healthier life. Proper nutrition depends, in large part, on whether you have Crohn’s disease or ulcerative colitis, and what part of your intestine is affected. It’s important to talk to your doctor. It also can be helpful to ask your physician to recommend a dietitian in order to develop a diet that works for you.

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Research is a vital part of developing new treatments and cures for autoimmune disorders. Plasma Med Research is currently looking for those with Crohn’s and UC to donate a small blood sample that will contribute to medical research.

If you, or someone you know is interested in participating, please reach out to us on Facebook, or at















Reprinted from:  Crohn’s and Colitis Foundation Resources


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