Dr David Silk (consultant physician, Central Middlesex hospital, London) pointed out that irritable bowel syndrome (IBS) produced a significant demand on the health services. It was the gastrointestinal condition encountered most commonly by general practitioners and by hospital specialists in gastroenterology, resulting in 1.1m consultations each year and costing the NHS around £45.6m.
Moreover, it was a multisystem disorder affecting more than the gastrointestinal tract. Non-abdominal symptoms such as fatigue, backache, urinary frequency, fibromyalgia and sleep disorders were common. Such symptoms were seen by some sufferers as more intrusive than the classical symptoms of abdominal pain, distension and altered bowel habit.
The cause of IBS was not fully known, although it was likely to be multifactorial in origin with stress, gastrointestinal infection, abdominal surgery, eating disorders, pelvic disorders, food intolerances, antibiotic therapy and child abuse acting as possible trigger factors. Although psychological factors could play a role in the exacerbation of the condition, the idea that IBS was purely a psychosomatic condition was untenable.
Traditionally, IBS had been thought to be purely a disorder of abnormal gastrointestinal motility, but abnormalities of gut sensitivity were now assuming an equally important role, said Dr Silk. In addition, IBS was a heterogeneous condition, and three subgroups of patients, each with different gastrointestinal symptoms, had been identified - those with spastic colon syndrome, those with functional diarrhoea and those with a primary motility disorder of the gut.
Patients with spastic colon syndrome experienced symptoms such as incomplete evacuation and pain associated with increased frequency of stools; opening of the bowels resulted in pain relief. Those with functional diarrhoea tended to have no pain, but they experienced faecal urgency, and the passage of several soft stools, usually first thing in the morning.
Primary motility disorder of the gut was associated with abdominal distension, postprandial fullness, nausea and anorexia, and abdominal pain not relieved by opening of the bowels.
The fact that patients experienced different types of gastrointestinal symptoms meant that therapy had to be carefully targeted. For example, no single dietary intervention, such as dietary fibre, would help all sufferers. Discussing the role of dietary fibre in IBS, Dr Silk pointed out that evidence of benefit from clinical trials was inconclusive. This was not surprising since trials had been limited by small numbers of patients, the use of single fibre sources, inadequate doses and a high placebo response.
In addition, the failure to understand that there were different sub groups of patients had led to negativity in the results. It was inconceivable that patients with motility disorder of the gut - experiencing symptoms of pain, gas and bloating - could obtain any benefit from fibre. Moreover, insoluble fibre, such as bran, could actually make the symptoms worse.
Patients with functional diarrhoea could benefit from soluble fibre because it was extensively degraded in the colon to produce short chain fatty acids - compounds that stimulated sodium and water reabsorption in the colon. Patients with spastic colon who had symptoms of diarrhoea would not benefit from fibre, while those with constipation would.
However, patients with spastic colon and constipation might not be suffering from IBS at all - the proper diagnosis could be slow transit constipation. The best thing to do with these patients was to increase their fibre and fluid intake and if there were no further problems, remove them from the "IBS list" so that they were not "labelled". Concluding, Dr Silk said that fibre had a role to play in the management of IBS, but only in carefully selected groups of patients.
According to Professor Jonathan Brostoff (consultant physician, Middlesex hospital, London), there was evidence that "yeast" was involved in some cases of IBS, and some patients had reduced numbers of lactobacilli and bifidobacteria (so-called "friendly" bacteria) in their guts. Indirect evidence came from the use of tetracyclines, which, when added to a standard stool population, increased yeast production and reduced counts of lactobacilli and bifidobacteria.
Lactobacilli might induce immunological hormones, which could alter mucosal response in the gut, and there was some evidence that different grains, such as wheat, oats and rice, altered the gut flora to varying extents. Low yeast diets had often been promoted for IBS, and although they were not a panacea, in the right patients, they could be successful, Professor Brostoff concluded.
Ms Gail Pollard (dietitian, Middlesex hospital) described the low yeast diet used at the Middlesex hospital. She emphasised that it was a low yeast rather than a no yeast diet. It was difficult to avoid yeast entirely without resorting to a diet consisting of elemental enteral feeds. Because sugar was considered to the main nutrient for yeast, the diet she recommended was low in both sugar and yeast. The initial diet involved cutting out cheese - yeast could be present in all cheese, not just blue cheese - and changing the type of bread eaten to soda bread, scones, poppadoms, chapattis and any other unleavened bread. Most alcoholic drinks had to be avoided, but because spirits were a highly distilled product, in which there would be little or no yeast left, they could be consumed in moderation.
All foods containing sugar had to be avoided. Although some people recommended avoidance of fruit, Ms Pollard recommended the consumption of two portions a day - preferably peeled to remove the yeast - because fruit was considered to be such an important part of healthy eating. Once the diet was established, symptoms could improve and foods containing yeast and sugar could be gradually - and often successfully - reintroduced, she said.
Dr John Hunter (consultant gastroenterologist, Addenbrooke's hospital, Cambridge) said that there was evidence of abnormal colonic fermentation in IBS, which could be associated with food intolerance. A trial at Addenbrooke's had shown that colonic hydrogen production was higher in patients with IBS than controls, and the use of an exclusion diet reduced both gas production and symptoms. Future developments in the management of IBS might therefore be related to modification of gut flora and there was much interest in the potential role of prebiotics and probiotics in this area. However, a trial of oligofructose (a prebiotic) at Addenbrooke's had shown no therapeutic value in patients with IBS, he said.