The following information is adapted from a leaflet published by the British Society of Gastroenterology & Digestive Disorders Foundation.

Introduction

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 diarrhoea (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.

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.
 

Causes

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.

Symptoms

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, diarrhoea 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.