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Diarrhoea And Irritable Bowel Syndrome

Diarrhoea And Irritable Bowel Syndrome

Diarrhoea And Irritable Bowel Syndrome


About one third of people with irritable bowel syndrome (IBS) have diarrhoea as one of their main problems. In many people, this can be controlled with simple measures, but in others the unpredictability of the bowel is a major problem. Unfortunately, some people are diagnosed as having diarrhoea-predominant irritable bowel syndrome (IBS-D) when in fact they have another condition such as coeliac disease.

Diarrhoea is the normal response of the bowel to infection or the presence of toxins. Increased muscle activity in the bowel wall, increased secretion of fluid into the gut and reduced absorption of the fluid all serve to help expel the infecting bacteria and toxins. Regardless of the cause, the symptoms usually feel the same – spasmodic abdominal pains accompanied by the need to rush to the toilet (urgency), where loose or watery stools are produced.

This process is usually self-limiting, ending within a few days or at most a few weeks. Problems arise if the process continues for some reason. For example, the infection giardiasis can persist in the small bowel for months or years. In coeliac disease, inflammation in the small bowel carries on because the immune system wrongly mounts a response to wheat. In inflammatory bowel disease (Crohn’s disease and ulcerative colitis), the cause of the inflammation remains unknown but can be severe enough to be life-threatening. And in irritable bowel syndrome too, low-grade inflammation, together with disordered control mechanisms, has been suggested as the cause of diarrhoea.

Bowel habit varies greatly between people, and an individual’s bowel habit will also vary over time. In surveys, up to a quarter of people report passing a loose stool at some time during the previous month. The occasional loose stool is probably due to something that was eaten or drunk, or even to unaccustomed exercise. Diarrhoea that lasts a few days or weeks is likely to be due to infection with viruses or bacteria. It can be very unpleasant but will normally settle without treatment. People usually seek advice if the symptoms are intolerably severe or if they last for more than a few weeks. They may expect an instant answer from their doctor, but unfortunately it can be difficult to distinguish between the myriad of conditions that present with diarrhoea and abdominal pain.

I’m opening my bowels far more frequently than I used to, and with softer stools. My stools are formed, soft blobs, or smooth and sausage-like. Is that diarrhoea?

Diarrhoea generally means watery stools, mushy stools or fluffy pieces with indistinct edges. What you are describing is a change in your bowel habit to looser more frequent stools, but not amounting to diarrhoea. There may be many causes, such as a change in your diet, greater caffeine intake or your exercise regime, as discussed in the questions below, but if you are older than 50, you should see your doctor to consider the possibility of more serious problems.

Could it be cancer?

The idea that it could be cancer suggests itself to most people who suffer from diarrhoea at some time. Indeed, it also worries their doctors. We are right to be a little obsessed with cancer of the large bowel (colon cancer or colorectal cancer). It is fairly common, with an average lifetime risk of 1 in 25 (compared with a risk of breast cancer in women of 1 in 9, and of prostate cancer in men of 1 in 6). Cancer of the large bowel causes about 20000 deaths in the UK and about 50000 deaths in the USA each year. More importantly, it develops slowly over 5–10 years, and it is potentially curable. At present, only about half of the people diagnosed with colon cancer are cured. But if it can be diagnosed at an early stage, or even when it is just a polyp (a small mushroom-like growth, usually not yet malignant), the cure rate can be much higher.

A change in the bowel habit to looser, more frequent stools that lasts for more than a few weeks may represent the first sign of bowel cancer. People with this symptom, especially if they are over the age of 50 (bowel cancer is rare under this age), usually need to have their bowel investigated; this normally involves a colonoscopy or a barium enema. Excluding bowel cancer as the cause of the diarrhoea is undoubtedly the most important role for the doctor. Unfortunately, once we are sure that the symptoms are not due to cancer, it becomes all too easy to attribute them to an irritable bowel. This may be true in most cases, but in others relatively simple diagnoses are being missed, hidden by the relief that it isn’t cancer. Part of the role of this section is to show how other conditions can masquerade as irritable bowel syndrome.

A problem for people with irritable bowel syndrome is knowing whether investigation is necessary at all. One of the key questions a doctor asks in order to determine whether it is necessary to investigate a person’s bowel is ‘Has your bowel habit changed?’ But people with irritable bowel syndrome often have such a disordered bowel habit that they cannot say if and when it has changed! Certainly, symptoms that have gone on for years are unlikely to be caused by cancer, but it is also possible that the symptoms of a ‘new’ cancer are being masked by those of a longstanding irritable bowel. Whether or not people with irritable bowel syndrome will have a colonoscopy or a barium enema to look at their bowel will very much depend on how they describe their symptoms, on their age and on when they had their last test.

Another problem is the embarrassment some people feel in describing certain symptoms. They may complain of diarrhoea when what they actually suffer from is leakage of the faeces, anal soreness or even frank incontinence of their stool. In others, the loose stool may not be as much of a problem as having to rush to a toilet at unpredictable times. This is called urgency of stool and denotes a problem with the rectum. Other people have to rush to the toilet frequently but then pass very little; these people may in fact turn out to be constipated. So it is vital that symptoms are defined as accurately as possible if the right diagnosis is to be reached.



I’ve had diarrhoea for almost a month now. What could be causing it?

Diarrhoea that continues for more than a few weeks has many causes; the most common are shown in Table 8.1. In otherwise well people, irritable bowel syndrome is the most likely cause.

I’ve had a change in my bowel habit over the past 2 months. I used to open my bowel once or twice a day with a formed stool, but now I go three or four times a day with a loose stool. I don’t pass any blood or mucus, and I don’t have to rush to the toilet. Apart from the loose stools, I’m a well 62-year-old man. What should I do?

You should see your doctor. He may find a simple explanation for the change in your bowel habit, such as a new medication or a change in your diet. If, after the change has been removed, your bowel returns to normal, all well and good. Otherwise, you need to be referred to the hospital to make sure that you don’t have bowel cancer. This will usually involve an examination of your bowel with a flexible sigmoidoscopy and barium enema or a colonoscopy (which involves inserting a tube with a small camera on into the lower end of your bowel)

Causes of persisting diarrhoea




This is an infection of the small bowel with a tiny, single-celled organism. It is commonly acquired on holiday.

Small bowel bacterial overgrowth

Occasionally, relatively harmless bacteria manage to proliferate in the normally sterile small bowel. They cause diarrhoea by impairing digestion and absorption. This is a common problem in those who are diabetic or elderly, and in people who have had surgery involving the small bowel.

Inflammatory bowel disease

There is excessive activity of the immune system in the gut. Its cause is unknown.

Ulcerative colitis

This affects only the large bowel. There is a need to rush quickly to the toilet, usuall with blood and mucus mixed in the stool.

Crohn’s disease

Abdominal pain and weight loss are common. Blood tests are often abnormal.

Cancer of the bowel

The average lifetime risk of bowel cancer is 1 in 25. The most common symptoms are a change in the bowel habit to looser, more frequent stools, and anaemia. It is rare under the age of 50.

Coeliac disease

This is an immune reaction to gluten, a constituent of wheat and barley. The immune system damages the lining of the small bowel. Food is therefore poorly digested and absorbed. Coeliac disease may affect up to 1 in 100 people and can show up at any age. There is a simple blood test to screen for coeliac disease.

Irritable bowel syndrome

Diarrhoea is common in this. However, it si not associated with weight loss or bleeding and does not usually occur at night.






Metformin is commonly used in diabetes.

Antidepressants (the type known as selective serotonin reuptake inhibitors)

These include Prozac (fluoxetine), Cipramil (citalopram) and Seroxat (paroxetine).


This is a drug used in asthma.


There are people who knowingly take laxatives yet complain of diarrhoea.





Lactose intolerance

Lactose is a sugar in diary products. A proportion of adults lose the ability to digest this sugar, which then acts as a laxative.

Fructose and sorbitol intolerance

Fructose is the main sugar in honey, many fruits and chocolate. In combination with glucose, it makes up sucrose, or table sugar. Sorbitol is used as a sweetener in ice cream, chewing gum, jam and diabetic foods. It is converted to fructose in the intestine. Some people have a lowered absorption of fructose, which then acts as a laxative.


Caffeine stimulates and speeds up the bowel. It is present in cola drinks, coffee, tea and chocolate.


Excess alcohol over a prolonged period frequently causes diarrhoea. It can be several weeks of abstinence for the bowel to recover.

Dietary fibre

Whatever the cause of the diarrhoea, increasing the fibre intake will usualy make it worse.


I recently had a colonoscopy to investigate the change in my bowel habit. They told me my bowel was completely normal, but I still have loose stools several times a day. What could it be, and what should I do?

People’s bowel habit does change with life. We take it especially seriously in people over the age of 50 because a change in bowel habit to loose stools may represent the beginning of bowel cancer. It’s possible that your current bowel habit is now the new ‘norm’ for you. If you are comfortable with this, nothing more needs to be done. However, it could be due to a number of other causes, some of which have simple solutions (see below). Some doctors, if they feel the risk of cancer is low, will actually look for these relatively simple causes of diarrhoea before embarking on a colonoscopy. If they were not considered prior to your colonoscopy, they should certainly be considered now.



I’ve heard of people getting diarrhoea from milk and other dairy products. How does this happen?

Lactose is a natural sugar contained in dairy products (milk, butter, cheese and to a lesser extent yoghurt). To digest it, we need the enzyme lactase. An enzyme is a protein made by cells to help chemical reactions, and there are many enzymes attached to the inside wall of the small bowel to help digest our food. Lactase acts on the lactose in the food, transforming it into glucose, which can then be absorbed. Some people lose most of their lactase in adulthood – this can happen to as many as 15% of Caucasians and up to 100% of Asians. Lactase may also be lost temporarily for up to 6 months following an infection.

If this happens, the lactose remains undigested as it passes down the small bowel. As with other sugars, it avidly draws water onto itself, and it holds the water in the bowel. As a result, more water enters the large bowel, and the stool becomes softer or even loose. In some people, a glass of milk per day can be sufficient to cause diarrhoea. Bacteria in the large bowel do digest some of the lactose to produce gas, so lactose intolerance is often accompanied by wind and bloating as well as loose stools.

Why do some people get lactose intolerance?

Actually, we believe that lactose intolerance is the ‘normal’ adult human condition and that man became tolerant to lactose simply because of a genetic mutation that meant the lactase enzyme continued to be produced into adulthood across some of the species. Lactase activity is high during infancy, but in most mammals, including most humans, it declines after weaning.

If lactose intolerance is the ‘norm’ in human adults, how is it that many adults tolerate dairy products without problems? Mutations in our genetic heritage often happen, but a mutation only becomes widespread if it offers some reproductive advantage to the individual possessing it. About 9000 years ago, humans began to domesticate cows, and milk became abundant for adults rather than just breast-feeding infants. Individuals who continued to produce the enzyme lactase were thus favoured as more of them were healthy and survived to have children, so the mutation became more prevalent through the process of natural selection. In some people, bacteria in the large bowel digest most of the lactose.

How can I find out if I’ve got lactose intolerance?

The simple way to find out if your symptoms are due to lactose intolerance is to avoid dairy products (milk, butter, cheese, yoghurt and milk chocolate). You should notice a dramatic improvement within a few days and certainly within a week. It is important to make sure that any improvement is not just a coincidence by then deliberately going back on dairy products to see if the symptoms recur. Even if you become convinced that your symptoms are due to lactose intolerance and you choose to avoid eating dairy products, you should try to reintroduce them from time to time as the absence of lactase may just be temporary.

I have lactose intolerance but I sometimes just can’t resist a cream cake and a bowl of ice cream! I pay for it afterwards with bloating and diarrhoea, but am I actually doing myself any harm?

The lactase is just acting as a laxative. It does you no harm at all. Enjoying the occasional cream cake will undoubtedly do you more good!

I have lactose intolerance. Is there anything I can do to reduce my symptoms?

Most people with lactose intolerance can tolerate small amounts of dairy products, for example still having milk in their coffee, and some dairy products are easier to tolerate than others. Hard cheese contains less lactose than soft cheese, and yoghurts are well tolerated because much of the lactose has already been fermented (broken up). Goats’ milk or cheese contains about 10% less lactose than cows’ milk, and soya milk has no lactose at all as it is of plant origin. Lactose-reduced cows’ milk products are also available. Drops or capsules containing the lactase enzyme are available and reduce symptoms when they are taken with dairy products. Do try all of these as they may help.

If you continue to eat dairy products, the bacteria in your large bowel that can metabolise lactose will be favoured over the others. As a result, your ability to tolerate lactose will increase. Conversely, if you avoid lactose altogether, you will have fewer lactose-digesting bacteria and your ability to tolerate lactose will get worse. Finding the balance between eating dairy products and getting symptoms is a personal choice.

Will my lactose intolerance cause me any long-term harm?

Only if it means you don’t get enough calcium in your diet – calcium is needed for healthy bones and teeth. Unfortunately, people who feel themselves to be lactose intolerant usually restrict their intake of dairy products but fail to make up their calcium intake. For example, a large survey from Finland, involving almost 12 000 middle-aged women, found that those with lactose intolerance consumed significantly less calcium (570 mg a day) than lactose-tolerant women (850 mg a day). Furthermore, the women who were lactose intolerant were more likely to require hormonereplacement therapy, or suffer a chronic health disorder or a bone fracture. There have also been other studies showing lower bone densities in people who are lactose intolerant.

It seems possible that people who experience symptoms following a generous serving of milk may avoid milk products in future despite the fact that smaller servings could be tolerated. Avoiding milk tends to make people more intolerant to it in the future because the bacteria in the large bowel will become less able to ferment the lactose efficiently. If avoiding dairy products becomes normal behaviour, bone density is likely to fall over a number of years, increasing the risk of osteoporosis and bone fractures.

If I decide to cut back on dairy products, where can I get more calcium from?

Only a limited choice of foods contain significant amounts of calcium – Table 8.2 shows some foods containing higher levels of calcium. The recommended daily intake of calcium for an adult (the RDA) is 800 mg. Supplement tablets don’t cost too much and usually contain 300–500 mg of calcium.

The calcium content is sometimes given in the nutritional information that now comes with foodstuffs. A full list can also be obtained from the US Department of Agriculture, Agricultural Research Service.

Sources of calcium


Calcium content (mg)

Plain yoghurt (small pot)


Rhubarb, frozen, cooked with sugar(1 cup)


Atlantic sardine, canned in oil and then drained (small can, including the bones)


Milk, low-fat(1 cup)


Spinach, cooked, boiled, drained and served without salt (1 cup)


Beans, white with mature seeds, canned (1 cup)


Pink salmon, canned, including the liquid and bones (small can)


White long-grain rice, parboiled and enriched (1 cup, dry)


Soya milk (1 cup)



Is fructose intolerance anything like lactose intolerance?

Fructose is the main sugar found in honey, many fruits and chocolate, and in combination with glucose it makes sucrose or table sugar. Sorbitol in the diet is also converted to fructose in the intestine. Sorbitol is used as a sweetener in ice cream, chewing gum, jam and diabetic foods. It may also form the base of some medicinal preparations such as antacids and multivitamins.

Some people have diminished fructose absorption. So if they happen to take more fructose than they are used to, the extra fructose will fail to be absorbed and will pass on into the large bowel. Here it will hold water within the bowel, acting as a laxative.

Fructose intolerance is a cause of watery diarrhoea and bloating. Avoiding fructose should alleviate the symptoms within a few days. If you have fructose intolerance but prefer to put up with a little diarrhoea after eating fruit and chocolate, no harm will be done.



I have heard of bacteria living in the stomach causing ulcers, and I have heard of ‘good’ bacteria living in the large bowel. Are there any bacteria in the small bowel?

The small bowel, where most of our digestion and absorption takes place, is normally almost sterile. It harbours few if any bacteria. By contrast, the large bowel is full of bacteria so that half the content of the usual stool is made up of bacterial cell bodies.

There are a number of mechanisms that keep the small bowel sterile. Acid in the stomach kills most of the bacteria that we ingest with our food. In addition, continuous rapid propulsion within the small bowel prevents the formation of stagnant pools of nutrients where bacteria can breed, and clears away any bacteria that have migrated up from the large bowel. There is also a valve between the small bowel and the large bowel that limits backflow.

But these mechanisms may fail, allowing bacteria to enter and proliferate within the small bowel. An excessive number of bacteria in the small bowel interfere with the digestion and absorption of food, causing diarrhoea. There may also be bloating, wind and weight loss. This syndrome is called small bowel bacterial overgrowth. Surprisingly, the bacteria do not actually invade the body from the small bowel, so there are no symptoms of infection. People with small bowel bacterial overgrowth do not usually feel unwell and do not have a fever. They usually report having diarrhoea, which can be watery or fatty. Alternatively, they may just feel that they have an irritable bowel.

Who gets small bowel bacterial overgrowth?

Anyone can get this disorder, but some people are more likely to. Elderly people produce less acid to sterilise their food, their immune system may be weaker, and the propulsive movement of their small bowel may not be as co-ordinated. In those with diabetes, those who have had surgery on their small bowel and those who have nerve damage, the movement of the small bowel may be disordered, leading to stagnation; this allows bacteria to propagate.

Does small bowel bacterial overgrowth cause irritable bowel syndrome?

The symptoms of small bowel bacterial overgrowth can be identical to those of irritable bowel syndrome, particularly diarrhoea-predominant irritable bowel syndrome (IBS-D). Bloating and diarrhoea are prominent in both syndromes. One American study of 111 patients with irritable bowel syndrome found evidence of small bowel bacterial overgrowth in 93 (84%) of the patients. Half the patients were treated with an antibiotic and half with an inactive medication (a placebo). About a third (35%) of the patients receiving the antibiotic improved compared with 11% of those who received the placebo. Although this study has not been repeated to confirm it, it does suggest that at least a proportion of patients with irritable bowel syndrome have small bowel bacterial overgrowth and will respond to treatment with antibiotics.

But there is much scepticism over this. I frequently treat patients with otherwise unexplained diarrhoea and bloating with antibiotics. In elderly patients, those with diabetes and those who have had surgery on their bowel or stomach, this is often the first therapeutic manoeuvre. A proportion of patients do show a benefit, making the treatment worthwhile, but most do not. You can discuss the possibility of antibiotic treatment with your doctor.

How do I know whether I’ve got small bowel overgrowth?

There are breath tests that look for the breakdown products of bacterial metabolism excreted in the breath. A sample of the contents of the upper small bowel can also be taken during an endoscopy (in which a tube with a camera is inserted into the gut via the oesophagus) and tested for bacterial infection. But contamination of the sample by the bacteria in the mouth usually makes the test useless. In fact, all the tests for small bowel bacterial overgrowth can be inaccurate, and the simplest approach is often just to try some treatment.

How can small bowel bacterial overgrowth be treated?

Many antibiotics will work, including metronidazole, ciproflox – acin, tetracycline and Augmentin. There may be a dramatic improvement over a week, although occasionally a month’s treatment is necessary. The infection frequently recurs, and further courses of antibiotics are used. Unfortunately, some people need almost continuous treatment with antibiotics. This may involve 2 weeks of ciprofloxacin followed by 2 weeks of metronidazole followed by 2 weeks of tetracycline and so on. Rotating the treatment is a way of keeping the bacteria sensitive to the antibiotics.

I asked my family doctor to prescribe antibiotics for me in case my irritable bowel syndrome was due to small bowel bacterial overgrowth. He was willing to do so, but reluctantly and with much scepticism. Why is that?

The infection in small bowel bacterial overgrowth is a mixed infection. Therefore, most antibiotics will reduce the number of infecting bacteria and should improve the symptoms. Antibiotics are very frequently prescribed for many different infections, but we don’t generally get people telling us how much better their irritable bowel syndrome is since the antibiotic they had for their chest, throat or urine infection. In fact, the opposite is more common: people more often tell us that the antibiotics have exacerbated their irritable bowel syndrome. Your doctor would be wary of this happening to you.



Are there other infections that can masquerade as irritable bowel syndrome?

Surprisingly, many people have never heard of the organism Giardia lamblia even though it is one of the most common parasitic infections in the world. Infection rates may be as high as 2–5% in the industrialised world. A staggering 20–30% of individuals in some regions of the developing world are infected.

Giardia lamblia is a one-celled organism that lives in the small bowel of both animals and humans. It forms cysts that are excreted in the stool, survive in fresh water and are relatively insensitive to chlorination. People become infected from water, food or drinks contaminated by the faeces of other infected people or animals. Many cases are associated with recent foreign travel.

The incubation period is 1–2 weeks, and the most common symptoms are diarrhoea with watery, foul-smelling stools, often with abdominal distension, flatulence, nausea, anorexia and vomiting. Most people will have a minor, self-limiting illness. Others may have a more severe illness and undergo tests, from which Giardia is recognised and treated. But in a significant number of people, the symptoms may arise gradually over a few weeks and may be troublesome rather than severe.

These individuals may not go to their doctor. If and when they do ask the doctor for help, the gradual onset of their symptoms and the length of time that they have been troubled tend to argue against an infection and towards a diagnosis of irritable bowel syndrome. People complain of loose, watery stools, bloating and excessive offensive flatulence going on for months or even years. They may be absolutely well in themselves, with nothing to suggest an infection or a serious illness. It is therefore easy for patients and their doctors to attribute the symptoms of giardiasis to an irritable bowel.

So does giardiasis cause irritable bowel syndrome?

Giardiasis does not cause irritable bowel syndrome, but it may be mistaken for it. Many doctors don’t appreciate how common it is even in developed societies. This confusion can mean that you may be treated for irritable bowel syndrome until the diagnosis of giardiasis becomes apparent.

How is giardiasis diagnosed?

The cysts of Giardia may be identified when stool is examined under a microscope. The problem is that the cysts may be excreted intermittently, so that even though an individual is infected, there may be no cysts in the stool. Moreover, the cysts can be difficult to see. Giardiasis can also be diagnosed by biopsies (samples of cells) taken from the duodenum at endoscopy. Here, the Giardia organisms are seen lying along the wall of the intestine.

More sophisticated stool tests will become available in the future. In the meantime, it is often better to treat people whenever there is a suspicion of Giardia.

If I have giardiasis, how will it be treated?

Giardiasis is usually treated with a 1-week course of the antibiotic metronidazole. The common side effects of this medication are a bitter taste, nausea and vomiting. Alcohol can make these side effects much worse.

A major problem in treating patients with Giardia infection is the recurrence of symptoms after standard courses of therapy. This may be due to several causes. First, the organism may be resistant to the treatment, so a longer course of metronidazole may be necessary. Second, the original infection may have been eliminated but the person may have become reinfected. Finally, the infection may have been eliminated, but the individual may be left with lactose intolerance (see an earlier question).



This is also known as coeliac sprue or gluten-sensitive enteropathy.

My friend’s just been diagnosed with coeliac disease. What is this?

The immune system has a large presence within the gut to protect us from any infection that we might ingest with our food. In coeliac disease, it makes a mistake and mounts a response to a protein constituent of wheat called gluten. Related proteins in rye, barley and possibly oats are also involved. The result is a low level of inflammation in the wall of the small bowel that damages its capacity to digest and absorb food.

The surface of the inner wall of the small bowel is designed so as to maximise its area. There are numerous folds, and the surface is covered by finger-like projections about 0.5–1.5 millimetres long that protrude into the intestinal lumen and are called villi. It is the villi that are principally damaged in coeliac disease. Indeed, they may be completely lost such that the inner surface of the small bowel appears flat. The consequence is a marked loss in surface area, which impairs digestion and absorption.

Although coeliac disease was recognised in ancient times, its association with wheat was only discovered by the Dutch paediatrician W. K. Dicke towards the end of the World War II. At that time, food, particularly the cereals used to make bread, was scarce in The Netherlands. Yet the condition of children with coeliac disease improved. Dr Dicke noticed that these children relapsed when bread was supplied at the end of the war by the Swedish Air Force. It was this serendipitous observation that led to the finding that wheat exacerbates coeliac disease.

Most of the damage is in the upper part of the small bowel, while the lower part of the small bowel may be unaffected. To a certain, but variable, extent, the unaffected small bowel makes up for the reduced function of the upper small bowel. This is one of the reasons why the symptoms of coeliac disease are so variable. Some people have a life-threatening illness with terrible diarrhoea and weight loss. Some have no symptoms at all, whereas others have symptoms that are easily interpreted as an irritable bowel, with bloating, flatulence, loose stools and abdominal pains.

Who gets coeliac disease?

Twenty years ago, we thought of coeliac disease as a rare childhood disorder. Today, we realise that it can become apparent at any age. There is a genetic susceptibility to coeliac disease that may affect as many as 1% of northern European Caucasian populations, but it is rare in people of African/Caribbean or Chinese origin. If you have coeliac disease, there is a 10% chance that your close relatives (parents, siblings and children) will also get the disease.

How is coeliac disease diagnosed?

With modern endoscopes, it is easy to take biopsies (samples) from the upper small bowel. When these are examined under a microscope, they have a loss or flattening of the villi, the finger-like projections on the bowel wall, together with an increase in the number of inflammatory cells. The diagnosis is confirmed by an improvement in symptoms, biopsy appearances or both with a gluten-free diet.

Over the past 20 years, simple and inexpensive blood tests for coeliac disease have been developed and refined. They test for evidence of an immune reaction to gluten by looking for specific antibodies in the blood. The tests are very sensitive, and coeliac disease is unlikely if they are negative. Occasionally, the blood test is positive but the patient does not have coeliac disease. So whenever the blood test is positive, a biopsy of the small bowel is necessary to confirm the diagnosis before treatment is started.

How do you treat coeliac disease?

Coeliac disease is treated with a gluten-free diet. Products containing wheat, rye, barley, and traditionally oats are avoided. The distant cousins of wheat, such as maize, rice and sorghum are safe, as is buckwheat, which is a legume rather than a cereal. Vegetables and meats are completely safe too.

On the face of it, eating a gluten-free diet seems relatively simple, but in practice it can be terribly difficult because wheat products are included in an enormous range of processed foods and may not be mentioned in the labelling. You need to be aware that hidden gluten can be found in some unlikely foods such as cold meat cuts, soups, soy sauce, many low or non-fat products and even licorice and jelly beans. A number of organisations provide regularly updated information about the contents of manufactured foods. Useful contacts include the Celiac Sprue Association of the USA, the Celiac Disease Foundation and Coeliac UK (see the Appendix for details).

Does coeliac disease cause irritable bowel syndrome?

No, coeliac disease doesn’t cause irritable bowel syndrome, but the symptoms of coeliac disease can be identical to those of irritable bowel syndrome, especially diarrhoea-predominant irritable bowel syndrome (IBS-D). Bloating and diarrhoea are prominent in both syndromes. Because coeliac disease involves the poor digestion and absorption of food, weight loss is an expected symptom and can be severe. By contrast, weight loss is unusual in irritable bowel syndrome. Surprisingly, though, many patients with coeliac disease do not lose weight. Indeed, I have diagnosed coeliac disease in severely obese patients! As a result, many doctors will perform a blood test for coeliac disease before diagnosing irritable bowel syndrome, just to make sure.

Coeliac disease is, however, frequently misdiagnosed as irritable bowel syndrome. In one study, 36% of people with coeliac disease had previously been diagnosed as suffering from irritable bowel syndrome.



What is inflammatory bowel disease?

The inflammatory bowel diseases are a group of conditions in which inflammation occurs and continues within the gastrointestinal tract. In ulcerative colitis, the inflammation is confined to the large bowel. In Crohn’s disease, any part of the gastrointestinal tract can be affected. What causes these conditions is unknown, and although they cannot be cured, they can usually be controlled. The inflammation in these diseases is usually considerably more severe than what is seen in coeliac disease or infections of the bowel. In ulcerative colitis, people commonly report diarrhoea with blood and mucus in the stool. In Crohn’s disease, abdominal pain and weight loss can be profound.

Can inflammatory bowel disease be mistaken for irritable bowel syndrome – they sound a bit similar?

The symptoms of inflammatory bowel disease can come on slowly over weeks or months. There may be a little abdominal pain, the stools may become a little loose, and people may feel somewhat tired. It is easy for them to interpret these symptoms as ‘an infection that will pass’ or as irritable bowel syndrome. In contrast to irritable bowel syndrome, however, the symptoms of inflammatory bowel disease do get worse. Diarrhoea occurring at night, weight loss and bleeding are also clues that the diagnosis is unlikely to be irritable bowel syndrome and should prompt people to seek medical attention.

Can inflammatory bowel disease cause irritable bowel syndrome?

Unfortunately, inflammatory bowel disease is frequently complicated by irritable bowel syndrome. It is a real problem, affecting up to half of people with ulcerative colitis or Crohn’s disease. In inflammatory bowel disease, there is excessive inflammation in the intestine, causing diarrhoea, bleeding and pain. This inflammation can usually be successfully treated by medication, but unfortunately even when the inflammation is completely suppressed, people may continue to have irritable bowel syndrome-type symptoms. It can be difficult to know if the loose stools, bloating and pain represent a recurrence of the inflammation or an irritable bowel following it.

In ulcerative colitis, the inflammation begins at the rectum, so it is fairly straightforward to perform a limited examination of the rectum to gauge the degree of inflammation. In Crohn’s disease, however, the inflammation can be anywhere in the gut, and a full examination of the entire gut is a major undertaking. Moreover, blood tests in Crohn’s disease can be normal even during a severe exacerbation. So whether the symptoms represent an exacerbation of inflammatory bowel disease or irritable bowel syndrome is often a matter of judgement. Treatment, as in many conditions may come down to experimentation to find what works best for you.

I’ve suffered from ulcerative colitis affecting just my rectum for many years, and I’ve always had a problem with diarrhoea, especially in the morning. My doctors tell me that there is now no active inflammation, but I’ve still got bad diarrhoea. What can I do? I’ve tried loperamide in the past and it didn’t work.

Loperamide does not work well when there is inflammation, but it may work extremely well when the colitis is in remission and there is no or little inflammation. If your diarrhoea is mainly in the morning, you can try one or two capsules of loperamide before going to bed.

. . . No, the loperamide didn’t work for me. And my doctor’s said that after many years of ulcerative colitis in the rectum, I now have a ‘micro rectum’. What does she mean?

She means that your rectum does not distend (expand) enough to hold the stool. As the normal rectum fills with stool, it expands so that the pressure within it remains more or less constant. Only when it is full does the pressure rise, sending us the message that we need to go to the toilet. In some people, after many years of inflammation in the rectum, the wall becomes damaged and will not stretch to accommodate the stool. So even a small amount of stool entering the rectum can elicit a ‘call to stool’.



You hear so much about dietary fibre these days. What exactly is it?

Dietary fibre is indigestible plant carbohydrate (mainly substances known as cellulose, pectins and lignins from the plant cell wall). It passes through the small bowel undigested to the large bowel where bacteria partially metabolise it into gas, liquid and short-chain fatty acids. The short-chain fatty acids are absorbed by the large bowel; these are an important nutrient for us. Most of what is left passes through the gut in the stool, along with water and gas trapped within it and bacteria growing on it. Fibre therefore produces a softer, wetter, bulkier stool that is easier to pass.

I have diarrhoea-predominant irritable bowel syndrome. Should I eat more dietary fibre?

If your diarrhoea is actually caused by constipation and overflow, more fibre may help. It may also help if you have alternating constipation and diarrhoea. However, since fibre holds water within your bowel, it is inevitable that, regardless of the underlying cause, more fibre will mean more diarrhoea.



Currently, the most potent drugs for slowing the bowel and relaxing its muscle are opiate based. ‘Opiate’ refers to drugs originally produced from the immature seed capsules of the opium poppy plant. Our nervous system produces its own opiate-like chemicals called endorphins. Their principal role is to reduce pain, and many of the cells involved in pain processing have receptors for the endorphin molecules on their surface. These receptors also interact with opiate drugs, so they’ve been called opiate receptors.

In the bowel, however, activation of the opiate receptors leads to relaxation of the bowel muscle and a profound slowing in function. This is why opiate-based analgesics (painkillers) such as codeine and morphine can cause severe constipation, and why opiate-based drugs can relieve diarrhoea.

Opiate medications used to treat diarrhoea


Trade names



Arrett Capsules, Boots Diareze, Diasorb, Diocalm Ultra, Imodium (including imodium liquid), Imodium Plus and Normaloe.

This is an opiate-based drug that acts selectively on the gut. As a result, it has little or no analgesic effect. There is also little or no risk of dependence. Drowsiness may be a side effect in large doses, but most people are virtually unaffected. A single dose of loperamide can remain effective for 24 hours.

Diphenoxylate and atropine


Diphenoxylate is similar to loperamide. The small dose of atropine in the mixture also slows the bowel by blocking the activity of another set of nerves (cholinergic nerves) that would otherwise increase bowel activity. In larger doses, atropine will cause unpleasant side effects such as a dry mouth and blurred vision. This means that Lomotil cannot be taken in large doses.

Codeine and dihydrocodeine

These are available over the counter in small doses, usually combined with paracetamol.

These are opiate-based medications used mainly as analgesics. They slow the bowel effectively, but are likely to cause drowsiness. Tolerance is a problem, which means they may becaome less effective over time. It is possible to becaome addicted to codeine.


Loperamide and irritable bowel syndrome

Loperamide is one of the few medications used in irritable bowel syndrome for which there is clear evidence that it is effective. It is usually very good when used to reduce or prevent diarrhoea. Usually, only small doses – one or two capsules a day – are necessary, sometimes even fewer. If your diarrhoea does not respond to loperamide, it may not be due to irritable bowel syndrome. Loperamide is safe to use in the long term, and the only significant side effect is constipation.

Loperamide is not an analgesic, which means that it is ineffective for pain. But sometimes the pain in irritable bowel syndrome is due to excessive muscular activity and spasm in the wall of the bowel. In such circumstances, loperamide may help.

Can loperamide make irritable bowel syndrome worse?

People with irritable bowel syndrome are often very sensitive to the effects of loperamide. A small dose can result in constipation with increased bloating and painful spasm. A loperamide syrup is available for children, but adults can use it to take very small doses.

What about Dioralyte? Could this help stop my diarrhoea?

Dioralyte is one of the oral rehydration salts available at phar – macies. Others include Rehidrat and Electrolade. They come as sachets of powder or effervescent tablets that are reconstituted with water. They contain sodium chloride (salt), potassium and bicarbonate, along with glucose to stimulate the absorption of these. Their purpose is to replace the water and minerals lost in severe infective diarrhoea.

The rationale behind this treatment is that some people with diarrhoea will only drink water. But drinking just water does not replace the salt and potassium lost in the diarrhoea, and moreover water taken on its own may not be well absorbed. Glucose not only acts as an energy source but actually stimulates the absorption of salt and water in the small bowel. A solution of glucose with salt, potassium and bicarbonate, with some flavouring to make it reasonably palatable, has proved very successful as a readily available, safe and cheap method of rehydrating people with severe infective diarrhoea, especially in the developing world.

Unfortunately, oral rehydrating solutions will not stop or reduce your diarrhoea. Their function is to replace the fluids and minerals that are lost. Personally, I prefer chicken soup.

My mother used to give me a liquid called Kaolin and Morphine whenever I had diarrhoea. What does it do, and is it still available?

Kaolin is a clay material traditionally used to soothe the stomach and the bowels. It is believed to absorb excess water, toxins and possibly bacteria, although this has never been formally tested. It is still available without prescription as Kaolin Light, or combined with a small dose of morphine. The morphine will reduce pain from spasm and slow the bowel down. Although it is present only in small amounts, there is a risk of drowsiness. As a treatment for diarrhoea, it is not as effective as loperamide.

An American friend has recommended bismuth subsalicylate for diarrhoea. What is it, and does it work?

Bismuth is a silvery metallic element whose compounds are used for various stomach and bowel problems and are still popular. It is believed that bismuth compounds may form protective coatings for inflamed surfaces such as ulcers. Bismuth itself may have antibacterial properties and has been used to protect against travellers’ diarrhoea. The subsalicylate portion of bismuth subsalicylate may improve diarrhoea by promoting absorption. It is available in the UK as Pepto-Bismol. For diarrhoea, it is not as effective as loperamide, and a large dose needs to be taken (30–60 ml or 2–4 tablets every 30 minutes up to eight doses). It causes temporary and harmless staining of your tongue, but don’t get it on your carpet!



Food passes straight through me. Whenever I eat, I feel a violent need to rush to the toilet to pass a loose stool. It’s very embarrassing as well as inconvenient. Despite this diarrhoea, I can’t lose weight. What’s happening?

This may not be true diarrhoea. You are actually describing a strong gastrocolic reflex. A reflex is an unconscious automatic response in which stimulation of one part of the body results in activity in another. For example, tapping the tendon under your knee leads to a reflex contraction of your thigh muscle, and your foot goes up. In the gut, filling and distension (expansion) of the stomach leads to nervous impulses that stimulate activity in the bowel. This is a normal reflex. It is stronger in some people than others, and it is often more prominent if you have irritable bowel syndrome or inflammatory bowel disease.

The simplest way of controlling this is to eat smaller meals, or to eat more slowly in order to reduce the distension of the stomach. Eating less fat may help too. Fatty foods tend to slow the emptying of the stomach, so a fatty meal will tend to distend the stomach more. You may also wish to avoid taking caffeine with your meal as it will increase the stimulation of your bowel.

Sometimes taking an antispasmodic medication such as peppermint oil or alverine citrate (Spasmonal) before your meals may help. These are usually available at the chemist without a prescription. A more potent alternative available on prescription is dicycloverine (dicyclomine, Merbentyl), which reduces spasm and slows the bowel down. Loperamide (Imodium) is good at slowing the bowel, and some people with a prominent gastrocolic reflex take a capsule before going out for a big meal.

I get sudden episodes of diarrhoea, especially when I’m stressed or rushing for the airport. What can I do?

If you can predict the circumstances in which your bowels may be overactive, you can take a loperamide (Imodium) capsule at an appropriate time, such as before going out.

I get diarrhoea at night as well as during the day. I have to get up several times during the night, and my sleep is badly disturbed. What can I do?

Diarrhoea at night is very unusual in irritable bowel syndrome. It is likely that there is a cause other than irritable bowel syndrome for your problem and you should see your doctor.

My main problem is first thing in the morning. The moment I wake up, I have to rush to the bathroom. The first bits I pass may be solid, but after that I have to rush several times to pass watery stools. What can I do?

This is a very common manifestation of irritable bowel syndrome. You could try a loperamide (Imodium) capsule before going to bed, or first thing in the morning.

I’ve tried loperamide, but even just one capsule will stop me going for several days! That can’t be good for me, and it’s certainly uncomfortable. What can I do?

People with irritable bowel syndrome are often very sensitive to loperamide. It’s a particular problem for those who have alternating constipation and diarrhoea. But Imodium syrup might help. This contains 1 mg of loperamide in each 5 ml dose, or the equivalent of half a capsule per spoonful. It’s then possible to take very small doses. Alternatively, you could try a small dose of Lomotil.

I’ve tried to slow my bowel down with loperamide, but it only works if I take eight or more capsules a day. I’ve also tried codeine, Lomotil and kaolin, but again they only work partially even in large doses. What should I do?

Your diarrhoea may not be due to irritable bowel syndrome. People with irritable bowel syndrome are usually very sensitive to medication that slows the bowel, such as loperamide. If loperamide doesn’t work, you should see your doctor to consider other diagnoses.

I’ve suffered from irritable bowel syndrome for many years. Some days I get diarrhoea, then at other times I’m constipated, and occasionally I’m OK. Over the last 3 months, things have changed so that I get diarrhoea all the time. It isn’t so bad that I can’t control it with loperamide, but I’m 65 years old and concerned about the change. What ought I to do?

You should see your doctor. There may be an obvious explanation such as a change in your diet or a new medication. However, if there is any doubt, an examination of your bowel to exclude cancer is important.

I’m only 32 years old. How concerned should I be about a change in my bowel habit? Like many people with irritable bowel syndrome, some days I get diarrhoea, but at other times I’m constipated. Over the past few months, things have changed so that I now get diarrhoea all the time unless I take one or two capsules of loperamide each day.

If you can control your bowels with one or two capsules of loperamide a day, it’s unlikely that your symptoms are anything other than irritable bowel syndrome. There may or may not be an obvious explanation such as a change in your diet or a new medication. But at your age, bowel cancer is very unlikely. If there is no weight loss, anaemia or bleeding, and no family history of bowel cancer, your bowel does not need to be examined.

. . . Yes, I understand what you are saying, but I can’t get the thought of cancer out of my head. I like my doctor, but I’m afraid he will laugh at me if I say I’m frightened about this. What should I do?

Doctors don’t usually laugh at patients; we prefer to laugh at other doctors! Physicians laugh at general surgeons, general surgeons laugh at orthopaedic surgeons, orthopaedic surgeons laugh at …, and so on. You would probably be surprised at how much understanding you get if you directly express your fear of cancer or any other disease. Most doctors, surrounded by illness as they are, have at one time or another thought they had a serious ailment. If your doctor laughs, he is more likely to be laughing with you than at you as he’ll have been there himself. So do go and book an appointment so that you can set your mind at rest.

My diarrhoea didn’t respond to any treatment. I had many tests, including a colonoscopy, all of which were normal. Finally, my doctor suggested cholestyramine (Questran). It worked! I’ve been told that my diarrhoea was due to primary bile acid malabsorption. What is that?

Bile acids are produced in the liver from cholesterol and secreted into the small bowel in the bile. Their function is to help dissolve, digest and absorb fat. In the last part of the small bowel, the terminal ileum, these bile acids are reabsorbed. They travel in the circulation back to the liver to be secreted again in the bile. But some people don’t reabsorb the bile acids well enough in the terminal ileum so that they pass into the large bowel. Here, they reduce the ability of the large bowel to absorb water and may actually stimulate it to secrete water. The consequence is a watery diarrhoea that may not respond well to antidiarrhoeal drugs like loperamide.

This failure of the terminal ileum to absorb the bile acids may be due to a disease such as Crohn’s disease. It also occasionally happens after a cholecystectomy (excision of the gall bladder), or it may be primary. By primary, we mean that we don’t know why it has occurred, and that it is not secondary to (a result of) anything else. Because all the usual tests are normal, the diarrhoea may mistakenly be attributed to irritable bowel syndrome.

Cholestyramine binds bile acids to make an inert complex. This complex passes through into the large bowel, where it has no effect at all. Cholestyramine was originally developed as a treatment for high cholesterol levels. As the bile acids are lost from the body when someone takes it, the liver is forced to produce a new supply. It uses cholesterol for this so the blood cholesterol level falls.

The problem with using cholestyramine is knowing how much to use. Too little and it is ineffective. Use too much and too many bile acids are lost. It then becomes difficult to digest fat. If fat is not absorbed, it passes out in the stool, causing a foul-smelling, yellow diarrhoea. It is really a matter of experimenting. I usually advise people to start with half a sachet of cholestyramine at night and increase this by half a sachet every 3 days or so depending on the response. If there is no improvement with one sachet four times a day, then it isn’t going to work and the diagnosis isn’t bile acid malabsorption.

As a tip, cholestyramine is more palatable if mixed with orange juice.

Recently, I decided to improve my diet by eating more fruit. I eat oranges, pears, grapes and apples. But instead of feeling well, my bowels have become loose, I feel bloated, and I pass a lot of wind. Why has this happened?

There are several possibilities. These fruits contain significant amounts of fructose. If you have an impaired absorption of fructose (an earlier question in this section discusses this), that would explain your symptoms. Or your loose stools might simply be a consequence of your increased fibre intake. It could also be just a coincidence, so the first thing to do is see if your bowel habit returns to normal when you revert to your old diet.

After many, many years of suffering from what I took to be irritable bowel syndrome, they finally diagnosed coeliac disease. I’ve been on a gluten-free diet for 3 months now, and I can’t believe how much better I feel. I’m still angry though that it took so long to diagnose my coeliac disease. It used to be very difficult to diagnose coeliac disease.

Twenty years ago, there were no specific blood tests for it. Hence, there was no simple screening test as there is today.

Moreover, if coeliac disease was suspected, proving the diagnosis meant getting the person concerned to swallow a large capsule attached to a long tube and waiting for the capsule to reach the small bowel. The capsule could then be activated to take one small biopsy (sample) and would have to be retrieved by pulling on the tube to which it was attached. It could take a whole day to get a specimen! Nowadays, getting a biopsy from the small bowel involves a gastroscopy (a telescopic examination of the stomach), which is usually straightforward. It’s probably because coeliac disease was so difficult to diagnose that we only recognised the more extreme cases.

Today, we realise that people with coeliac disease can have a wide range of symptoms. We usually test for coeliac disease with a blood test when people report loose stools, excess wind, bloating, weight loss or fatigue. Although patients with coeliac disease tend to be thin, it has been diagnosed in people who are actually obese. It is likely that there are many people who put up with symptoms that they attribute to irritable bowel syndrome when in fact they have coeliac disease.

It’s good that your doctor recognised the possibility of coeliac disease masquerading as irritable bowel syndrome. As more and more doctors do so, there will less delay in diagnosing coeliac disease in the future.

I thought I had coeliac disease, but the tests were negative. Even so, I put myself on a gluten-free diet, avoiding anything that contained wheat or barley. Giving up bread was a major sacrifice, but I feel enormously better. I no longer have diarrhoea, I don’t bloat nearly as much, and I get a lot less noise from my stomach. Could the tests have been mistaken?

Unfortunately, no test is perfect. However, it is unusual for people with a negative blood test to turn out later to have coeliac disease. It is even more unusual for biopsies (samples) from the small bowel to miss a diagnosis of coeliac disease. It can happen, though, and we do occasionally repeat the tests.

But there are other possible explanations for why you are feeling so much better on a gluten-free diet even if you do not actually have coeliac disease. A gluten-free diet often means eating less fibre. Some patients with irritable bowel syndrome, particularly those who have mainly diarrhoea, feel much better with less fibre in their diet. If this is so in your case, you may be able to eat bread again if you reduce your intake of fibre from other sources.

Alternatively, some people with irritable bowel syndrome are simply intolerant of wheat and wheat products. We don’t know why an intolerance like this develops, but in contrast to coeliac disease it is not due to an activation of the immune system. Moreover, eating wheat may cause symptoms but it does not cause any damage or long-term harm. So people who are intolerant of wheat but do not have coeliac disease don’t need to be as strict with their diet as people with coeliac disease. In fact, they should experiment from time to time with wheat products to see if the intolerance is persisting and how much wheat they can actually tolerate.

I suffered from diarrhoea and had a colonoscopy. They told me it was all normal, but when I came back for a follow-up appointment, I was told that actually the biopsies showed microscopic colitis. What is that?

Microscopic colitis is a colitis that is only diagnosed when biopsy specimens from the bowel are examined under the microscope and show excess inflammation. This colitis is mild, and without a microscope the wall of the bowel looks normal. It may represent a mild form of ulcerative colitis with no ulcers and hence no bleeding, or it may represent another form of colitis such as what are called lymphocytic colitis and collagenous colitis. These disorders usually show up in middle age with persisting watery diarrhoea. They do not progress to anything more serious and are usually treated with a type of anti-inflammatory medication called mesalazine

. . . . Yes, I was treated with mesalazine. But it didn’t work. They had another look at my bowel, and this time they told me that my bowel looked normal. They took a lot more biopsies, and they were also normal. So now they’re saying that I don’t have microscopic colitis, it must be irritable bowel syndrome after all! What’s going on?

The diagnosis of microscopic colitis depends on a somewhat subjective assessment of the degree of inflammation in the biopsy specimens. A second look, with more biopsies, can clarify the diagnosis.

It is also possible that the original microscopic inflammation was due to a previous infection. This infection has now cleared but left you with an irritable bowel. This is called postinfective irritable bowel syndrome (IBS-PI). In surveys, about 10% of people with an irritable bowel recall an infection that seemed to set off their irritable bowel syndrome. In studies of previously well people diagnosed with bacterial gastroenteritis, 7–31% developed an irritable bowel in the 3–6 months after the infection. Gastroenteritis, either viral or bacterial, is an important cause of irritable bowel syndrome. The diarrhoea is usually easily controlled with loperamide.

How long does postinfective irritable bowel last?

There isn’t much information with which to answer this question, but one study suggests that 6 years after a diagnosis of postinfective irritable bowel syndrome, fewer than half of the people affected had recovered.