Introduction
In many ways the best treatment for Crohn’s disease is diet. This can lead to long remissions without the risk of the side effects produced by so many drugs and may reduce the need for surgery. However the diet varies from one patient to another and must be tailored to each individual carefully and conscientiously under the supervision of a qualified dietitian.

How do diets work?
Food residues which have not been digested and absorbed in the small intestine pass down into the lower bowel and are fermented by the bacteria that live there. It is believed that an immune reaction against the bacteria living in the bowel is a very important factor in the cause of Crohn’s disease and that the activity of these bacteria can be modulated by diet. Diet does not work in Ulcerative Colitis, probably because the bacteria involved rely not on food residues but on substances which naturally occur in the bowel, such as mucus, for their energy requirements. The reaction to foods is quite different to allergy where special antibodies are circulating in the blood. This means that skin prick and blood tests for allergy are of no help in deciding which foods need to be avoided.

How is a Crohn’s diet constructed?
There are 3 stages in dietary treatment:
1. The patient stops eating normal food stuffs and is given a liquid enteral feed as the sole source of nutrition. Symptoms normally disappear after 2-3 weeks.
2. When all symptoms have cleared normal foods are reintroduced to see which ones cause symptoms and which ones may be eaten without difficulty. Those provoking symptoms are subsequently excluded.
3. When all foods have been reintroduced those irritating the bowel are tried again to make certain they genuinely cause difficulties and the dietitian checks the resulting diet to make sure it is nutritionally adequate and advises on any supplements needed.

Enteral Feeding
This is the crucial first stage of dietary treatment which appears to be essential for success. Enteral feeds are the best medical treatment for Crohn’s disease currently known, as 85-100% of patients who continue to take them for the 2-3 weeks required will enjoy a full remission. This is considerably better than steroids or infliximab.

Enteral feeds are a by-product of the space race and were originally developed by NASA to feed astronauts. They are made from the basic building blocks of foods, so that the nutrients are easily available for rapid absorption in the upper small intestine, and there is little if any residue for fermentation by gut bacteria. The feeds contain sugars, an oil to provide fat, and single or short chains of amino acids or simple protein; minerals and vitamins are added as required to make the feeds nutritionally complete.

Enteral feeds are divided into elemental feeds, which contain single amino acids, oligopeptide feeds, which contain short chains of amino acids, and polymeric, which contains simple protein derived from a single source. These differences may affect taste. 95% of patients drink enteral feeds straight from the cup, but sometimes they prefer administration by a fine tube through the nose into the stomach.

Enteral feeds are normally taken for 2-3 weeks although this is often extended in children. A quantity of liquid feed is usually built up over a few days until the individuals requirements are met as determined by a dietitian. Most patients need 2-3 litres daily. No other food or drink is allowed except bottled water although this advice may vary between hospitals. The feed should be sipped throughout the day and is better if kept chilled. Symptoms are recorded regularly and when they have resolved the patient is ready for stage 2.

Reintroduction and testing of foods
At present no test exists to allow us to determine which foods will provoke symptoms. Each new food item must be eaten to see what effects it produces.

The simplest way to do this is an elimination diet. One new food is introduced each day and consumed in generous quantities 2-3 times on that day. If symptoms develop it is subsequently avoided whilst foods that cause no problems are left in the diet. In this way a ‘safe’ diet is gradually built up. Some foods need to be tested for longer periods as the onset of reactions may be slow. The enteral feed is gradually reduced in amount as the diet widens. The elimination diet is slow and often tedious; it may take 2-3 months to complete the testing process.

With increasing experience it has been possible to simplify and shorten the process by means of the LOFFLEX diet. This is a LOw Fat, Fibre Limited EXclusion diet, which allows the patient to eat quite a wide range of foods that rarely upset people with Crohn’s Disease. On reaching remission the enteral feed is stopped completely and the LOFFLEX diet is followed for 2 weeks. The number of foods remaining to be tested is therefore less and food reintroduction is quicker and easier. These days, most patients test foods this way. However, if symptoms return during the 2 weeks on the LOFFLEX diet it is necessary to use the elimination diet instead.

Sometimes reactions to food may be unpleasant and prolonged. In most cases the symptoms subside if the patient keeps to foods which he knows to be safe. It may be quicker to return to the enteral feed for 2-3 days to get everything settled as rapidly as possible so that further food testing can continue.

Food intolerances discovered by patients with Crohn’s disease vary. The most important are wheat and gluten, dairy products, maize or corn, and yeast. However, some patients may be upset by a number of other foods particularly those that are high in fat or fibre; unlike coeliac disease, a single diet where 97% of patients respond to gluten free diet, a single diet for Crohn’s disease does not exist.

Re-challenging foods and nutritional assessment
When all foods have been introduced those which caused problems are retested to confirm that the reaction was genuine and not mere coincidence. If so the food is excluded for at least 6 months, but it is sensible to retest from time to time as food intolerances slowly become less severe and after 5-10 years usually diappear completely.

Nutritional assessment is essential to check that the final diet is adequate. Foods which have been excluded must be replaced with suitable alternatives and vitamin and mineral supplements such as calcium may be required.

The construction of a diet for Crohn’s disease is thus a complex procedure; it is essential it is done under medical and dietetic supervision. Eliminating foods without proper testing and dietary assessment can result in a nutritionally inadequate diet.

Advantages of diet
The development of Crohn’s disease is a cascade starting with the bacteria in the lumen of the bowel, which lead to the triggering of complex inflammatory reactions in the gut wall and tissues beyond. Diet targets the inflammatory cycle at the very beginning, thus can be more effective than treatments such as corticosteroids or infliximab, which interrupt the inflammatory cascade at a lower level.

Furthermore, the patient has control over the disease and its treatment. If mild relapses occur they can be controlled quickly without medical intervention. Patients understand how to avoid running into difficulties at times of holidays, celebrations and other major events when they particularly wish to be well.

Diet allows long remissions of Crohn’s disease. Once the process of foods testing is complete it is unusual for patients to relapse. After a year of successsful dietary treatment most patients remain completely well and find after 5-10 years their diet has returned to normal, the Crohn’s disease having apparently burnt itself out completely.

The diet does not have the side effects associated with drug treatment. In particular there is a very much reduced risk of osteoporosis. In a study of 95 female patients treated by steroids, diet or mainly by surgery, it was found that the diet group’s bone density was similar to that of age matched normal controls, whereas it was significantly reduced in those treated mainly by steroids.

Further reading:
• Dear KLE, Compston JE, Hunter JO. Treatment for Crohn’s disease that minimise steroid doses are associated with a reduced risk of osteoporosis. Clinical Nutrition. 2001; 20 (6): 541-546
• Riordan AM et al. Treatment of active Crohn’s disease by exclusion diet: an East Anglian Multicentre controlled trial. Lancet. 1993; 342: 1131-1134.