Elemental and Polymeric Diets in Crohn’s Disease

A liquid diet taken in place of all normal food for a period of weeks is one of the most effective treatments for active Crohn’s disease (CD). The process is known as exclusive enteral nutrition (EEN). The feeds themselves fall into two main groups, elemental and polymeric, with semi-elemental feeds lying in between. This page explains how they differ and what to expect if your doctor or dietitian suggests one.

What is the difference?

All of the feeds are nutritionally complete, meaning that they contain all the energy, protein, vitamins and minerals the body needs. The difference lies in how far the protein has been broken down before you drink it.

1. Elemental diets contain protein broken down completely into individual amino acids. The carbohydrate is mainly simple sugars and the fat content is low. Virtually all of the feed is absorbed high in the small intestine, so very little residue reaches the lower bowel. Elemental 028 Extra is an example.
2. Semi-elemental diets contain protein broken down into short chains of amino acids (peptides). Pepdite 1+ is an example.
3. Polymeric diets contain whole protein, usually from milk. They are closer to ordinary food, taste better and are less expensive. Modulen IBD is a polymeric feed often used in children.

Do they work equally well?

Clinical trials comparing the different types have generally found that polymeric feeds are about as effective as elemental feeds at bringing CD into remission, provided they are taken properly and exclusively. As explained in ‘Which dietary treatment should I choose?’, the fat content of the feed seems to matter more than the form of the protein, and feeds with more than 15% of their energy as long chain fats appear less effective.

In practice the choice depends on the individual. Elemental diets work more quickly, usually within 2-3 weeks, while a polymeric diet is normally taken for 6-8 weeks. Some people cannot manage the taste of an elemental feed for long, while others find a shorter course easier to cope with, even if the taste is less pleasant.

Which patients are suitable?

Liquid diets are most often used for CD affecting the small intestine, but they can help when the colon is involved too. They are suitable at the time of diagnosis and for later flare-ups, and may be used to improve nutrition before surgery. A liquid diet can also help when the bowel has become narrowed (a stricture) and solid food causes pain, although this should be discussed carefully with your specialist.

Liquid diets do not work in ulcerative colitis (UC).

Children

In the UK, EEN is the preferred first treatment for most children with active CD. It is at least as effective as steroids in children, and it avoids the effect that steroids have on growth. Children usually take a polymeric feed for 6-8 weeks, and growth often picks up once the disease has settled.

Taking a liquid diet

A dietitian will work out how much feed you need each day, which for most adults is 2-3 litres. The amount is built up gradually over several days, particularly with an elemental diet, as these draw water into the bowel and may cause diarrhoea if started too quickly.

Some practical points:

• Sip the feed slowly throughout the day rather than drinking large amounts at once.
• Most people find the feed tastes better chilled. Drinking through a straw also helps.
• Flavourings are available for some feeds. Your dietitian will tell you which are allowed.
• Plain water is usually allowed. Other drinks, including tea and coffee, are not normally permitted, although this advice varies between hospitals.
• Do not eat any other food, however small the amount. Even a little food may stop the diet from working.

Most people drink the feed, but some prefer to have it given through a fine tube passed through the nose into the stomach (a nasogastric tube). This is often done overnight, which leaves the day free and avoids the problem of taste altogether. The tube is quick to learn to use and many children manage it well.

Common problems

Hunger. The first few days are usually the hardest. Hunger tends to ease once the full amount of feed is being taken.

Taste. The feeds, particularly the elemental ones, are an acquired taste. Chilling the feed and changing flavours regularly can help.

Change in bowel habit. Because so little residue reaches the lower bowel, the motions become fewer and smaller. Some people go several days without opening their bowels. This is expected and is not usually a cause for concern. Diarrhoea in the early days usually settles if the feed is taken more slowly.

Social life. Meals are part of family and working life and this can be one of the hardest parts of the diet. It may help to plan the diet for a time when there are no holidays or celebrations, and to explain to family and friends why you are not eating.

Weight. Most people gain weight on the diet, particularly if they have lost weight during a flare-up.

What happens afterwards?

When the symptoms have settled, normal foods are reintroduced one at a time to find out which ones cause problems. This is the most important stage of dietary treatment, because without it symptoms often return within a few months. The feed is gradually reduced as the diet widens.

The simplest way of reintroducing foods is the LOFFLEX diet, which allows a wider diet to be built up more quickly than testing each food individually. The full process is described in ‘The Dietary Treatment of Crohn’s Disease’.

Some people also take a smaller amount of feed alongside their normal diet for a longer period, to help keep the disease in remission. This is called partial enteral nutrition.

Obtaining the feeds

Elemental and polymeric feeds are available on NHS prescription when they have been recommended by your hospital team. Meal replacement drinks sold in shops are not the same. They are not designed for the treatment of CD and should not be used for this purpose.

A liquid diet is a medical treatment and it is essential that it is undertaken under medical and dietetic supervision.