Irritable bowel syndrome (IBS) is a common digestive disorder which can cause troublesome and persistent symptoms. These vary greatly from person to person, but usually include cramping discomfort, a feeling of fullness or bloating, and a change or disruption of bowel habit. This can range from constipation (difficult or infrequent passage of a motion) to diarrhea (frequent or loose motions and an urgent need to go), or can alternate between the two. 

The symptoms appear to be due to an increased sensitivity of the bowel, which results in spasm of the bowel muscle. IBS is a disorder of the way in which the bowel functions. For this reason, it is sometimes referred to as a ‘functional bowel disorder’. 

The irritable bowel syndrome is not: 

• hereditary, although other members of the family may have similar symptoms; 
• food allergy, although some patients find they are intolerant of particular foods; 
• "all in the mind", even though test results may be normal; 
• an infection, although it may have been triggered by an initial attack of gastro-enteritis; 
• bowel inflammation, as in the case of ulcerative colitis or Crohn’s disease; 
• caused by ulcers, gallstones, cancer or other more serious digestive diseases, although some patients with these conditions may have some symptoms in common with IBS at some stage.

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The irritable bowel syndrome is extremely common in developed countries. More than half of all patients attending gastroenterology out-patient clinics have IBS. A third of people in Britain have occasional symptoms of IBS, and 1 in 10 have symptoms bad enough to require medical attention. Women tend to seek medical attention for it more often than men, but the prevalence in men and women is similar. IBS commonly starts between 15 and 40 years of age, but may occur at any age.

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The symptoms differ between patients and may vary from time to time, but all patients will have at least some of these: 

• Abdominal pain, which is often colicky in nature. It may be felt anywhere in the abdomen, but is often low down on the left. Many patients find their pain is worse when constipated, and it may be relieved by opening the bowels or passing flatus (wind from the back passage). In women there may be a pattern associated with their periods. 
• Fullness and bloating, making clothes feel tight and uncomfortable and sometimes associated with rumbling noises and flatulence (wind). The abdomen may feel tender. Belching and passing wind through the back passage can ease this. Nausea can occur but vomiting is not usually a feature of IBS. 
• Alteration in bowel habit, which may be constipation, diarrhea or an alternation between the two. Bowel habit varies enormously between individuals, though most people have their own pattern. The change in bowel habit may be in the frequency of action, the form of the motions, or associated urgency (rushing to go). There may be some discomfort or difficulty in opening the bowels. A sensation of incomplete emptying is common. Ineffectual straining to pass a motion (tenesmus) and a sharp pain felt low down inside the back passage (proctalgia fugax) are also common. Incontinence can occasionally occur, causing great embarrassment and anxiety. 
  

Though some of these symptoms may be embarrassing or distressing, it is important to tell the doctor about them. Worrying in silence may make them feel even worse. Remember, they happen to a lot of people. 

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 The cause of IBS is not fully understood yet. Research has shown that the bowel in IBS sufferers is more sensitive than usual and this sensitivity sets off a reaction which causes the symptoms. Understanding the normal muscle control in the bowel helps to explain what happens in IBS. 

The bowel is a muscular tube which propels food from mouth to anus, allowing nutrients to be digested and absorbed along the way. The colon (large bowel) links the small bowel to the rectum and anus (back passage), and is the source of most of the symptoms of IBS. It acts as a reservoir for the semi-liquid residue of the digestion of food, and absorbs water and salts from this, leaving a more formed motion to be passed. Regular muscular contractions propel the contents through the colon. If the bowel is overactive, the contents pass more rapidly and the patient gets diarrhoea, whereas sluggish activity causes constipation. Muscle spasm in the bowel causes discomfort and cramping pain. Eating a meal, or the presence of gas in the bowel, can trigger contraction and spasm, causing symptoms. 

Anxiety, depression and stress related pressures of life are commonly associated with IBS. Feeling low may occur as a result of distressing bowel symptoms, but in some it occurs spontaneously and seems to aggravate the problem. Symptoms of IBS may increase stress because of fears that there is some serious disease present. 

The nature of the diet, eating habits and lifestyle also influence the way the bowel functions. Too much, or too little, dietary fibre; too much fat; or a very rich or spicy diet may all upset the working of the bowel and trigger the symptoms of IBS. 

Alcohol, coffee, tea and smoking can all act as stimulants to the bowel and provoke an attack. For some people, certain foods may have the same effect. However, often there is no obvious precipitating factor. 

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Investigations are important to exclude other more serious bowel disorders that can produce similar symptoms to those of IBS. The history of the symptoms and a physical examination will help to establish the diagnosis. In many young patients, the doctor may diagnose with a few initial investigations and treat the disorder. In older patients who develop new digestive symptoms, the doctor will do more extensive investigations to exclude other bowel disorders. Laboratory tests, x-rays and endoscopy (internal examination with an instrument) may be done to exclude other digestive disease. The response to a trial of treatment may help to establish the diagnosis. If some of the symptoms are not typical, such as weight loss or blood in the motions, full investigation is essential. 

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Although the irritable bowel syndrome may produce troublesome symptoms, it does not lead to serious complications. It is important to know and understand this. An explanation of the disorder and how symptoms are produced helps to relieve anxiety and allows the patient to cope better with the symptoms. If attacks are infrequent or mild, this insight may be sufficient. Reassurance that more serious or progressive disorders are not present is also important. A knowledge of what provokes an attack may help individuals control their symptoms more effectively and prevent attacks, or at least help them to cope better. 

Advice on diet, eating habits and lifestyle helps many IBS sufferers. A well-balanced ‘healthy’ diet, taken as regular meals, will reduce symptoms. Some patients benefit from increasing the fibre content of the diet and others may be helped by reduction in fibre intake. Important foods containing fibre are cereals, fruit and vegetables. Fibre supplements prepared from plants can be prescribed or obtained from the chemist, but these should not be used without first discussing the symptoms with a doctor. 

Foods which are high in fat often provoke symptoms and should be avoided. Rich or spicy foods can also cause attacks. People usually are aware of particular foods which upset them, but may not associate attacks with common foods such as dairy products, bread and cereals, which can trigger symptoms. Large, infrequent meals challenge the digestion much more than small, frequent ones, which often help to reduce symptoms. 

Patients who relate their symptoms to stress or anxiety usually benefit from a better understanding of the condition. Sometimes counseling in stress management is helpful. Others with more severe symptoms may benefit from hypnotherapy. If anxiety or depression are a major part of the problem, psychotherapy may help. Treatment with an antidepressant may also reduce symptoms. 

Antispasmodic drugs help some patients, but response is variable. Constipation may require additional laxative treatment under medical supervision. Diarrhea can also be controlled, particularly if it is limiting activity, mobility and lifestyle. 

In many cases, reassurance, explanation and symptomatic treatment are all that is required and regular medication is not necessary. 

Read also: What medication is there for IBS?.

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Despite considerable research, the cause of irritable bowel syndrome remains in-completely understood and there is, as yet, no cure. It is well established that the symptoms of IBS are due to the way in which the bowel functions, rather than any specific disease of the bowel. With new research methods, which the Digestive Disorders Foundation is supporting, it is becoming possible to monitor the functioning of the bowel and to understand it better. It is hoped that this will provide more specific and effective treatments for the troublesome symptoms of this common condition. Fortunately, most patients’ symptoms are reasonably controlled most of the time by the treatments outlined. For some, the symptoms often resolve on their own with time. However, there is a continuing need to sustain further research into IBS, to help relieve the symptoms for sufferers and to advance our understanding of the functioning of the bowel.

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