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Irritable Bowel Syndrome

Irritable bowel syndrome or “IBS” is a common disorder of the gut characterised by bouts of abdominal pain, bloating and often a mixture of diarrhoea and constipation. On testing, there is no obvious abnormality in the gut such as inflammation, infection or tumour. It most commonly affects adults in their 20’s to 40’s and affects as many as 1 in 3 people in Europe and the US.

Irritable bowel syndrome is usually a diagnosis made by exclusion of any detectable abnormality in the gut and the term IBS tends to be used as a catch-all, despite people having a range of different symptoms and presentations. Conventional treatments are generally rather limited and it is no surprise that many people seek help and advice from complimentary medical practitioners. 

Specialist in this area:
Prof Jeremy Sanderson
Dr Jason Dunn
Dr Phil Berry

Bloating and fementation in IBS

In fact, although there is a lot of overlap, IBS can be broken down into a number of conditions with varying influences which, importantly, need very different treatment approaches. These are as follows:

Post-infective IBS

This is one of the commonest forms, usually comprising a tendency to loose stools and gas, coming on after an acute episode of gastroenteritis (eg travel diarrhoea or food poisoning). In most cases this resolves with time. Specific intolerances are common, especially milk products (lactose intolerance). Treatment generally involves keeping the diet simple and non-stimulatory and reassurance that normality will return with time (usually weeks or months but can be years). More specific diets such as the low FODMAP diet can help, probiotics, and occasionally antibiotics either if persisting infection (eg Giardia) is present or there is good evidence of small intestinal bacterial overgrowth (SIBO) present (see separate section on SIBO).

Constipation-predominant IBS

This is also very common and in most people should be referred to as constipation rather than IBS. Constipation can mean many different things in different people including infrequent bowel actions, passage of hard stools and lack of an urge to go to the toilet. There is often abdominal pain and particularly bloating and gas. The right treatment depends on determining the cause which can relate to slow transit through a colon, mechanical emptying problems, occasionally general health problems and issues with diet and lifestyle. An increase in fibre, particularly wheat, usually leads to more bloating rather than benefit and appropriate dietary advice in this group is very important. Newer medical treatments are also available for refractory cases (linaclotide, prucalopride). Mechanical emptying problems are often best managed by assessing the physiology and anatomy of the lower part of the bowel and techniques such as biofeedback or, in some cases, surgery can help significantly. 

Diarrhoea-predominant IBS 

This is perhaps the least well understood variant of IBS in which patients develop loose stools, often without pain but there may be gas and bloating, with no clear trigger. Diarrhoea is common after meals (giving a sense that food goes straight through) and “intestinal hurry” is quite a good description for the condition. There are many causes of diarrhoea predominant IBS, some unknown, but includes stress and anxiety, microscopic inflammation, changes in the bacterial flora and bile salt related diarrhoea. The role of bacteria is controversial but there is almost certainly a group of people, particularly with bloating as well as diarrhoea, who may have an overgrowth of bacteria in the small bowel (SIBO) and who may benefit from antibiotics and/or probiotics – see SIBO and Breath test section.

Mixed or “alternating” IBS 

In this group, patients tend to vary between diarrhoea and constipation – i.e. there is no fixed pattern. This group is perhaps the one in which stress and anxiety plays a bigger part in the cause. Whether this is because stress leads to altered diet and lifestyle (no time to look after yourself!) or a direct effect of the stress, for example on the nerves of the gut, is uncertain. The gut has more nerves than the brain so it is no surprise that stress and anxiety will have a profound impact (just think how most people are when they go for an interview). It is difficult to determine the factors contributing to symptoms in any particular person but it is important to treat each case individually as a different mix of factors is present in everyone. Whilst diet and lifestyle changes are important in most, addressing psychological issues formally may also be important, for example with cognitive behavioural therapy (CBT), psychotherapy and, in some cases, anti-anxiety drugs. 

Causes and Diagnosis of IBS

Is food allergy a factor in IBS? 

Many patients ask about food allergy, for obvious reasons. In fact, true food allergy is rare (an allergic reaction is generally an acute reaction to a specific food such as peanut or seafood allergy). Most patients (in fact nearly all) with IBS do not have a food allergy. Food intolerance, on the other hand, is more common but difficult to define. The gut is designed for food and therefore, by definition, meal related symptoms are a food intolerance. Specific food intolerances are common in IBS. Milk (lactose) intolerance is often present in post-infective IBS but less often in other cases. Wheat intolerance is much talked about and is certainly a common problem in IBS. The main problem with wheat relates to excessive fermentation (not an allergy) and the main symptom is therefore bloating. 

Bloating and Fermentation in IBS 

Bloating is one of the commonest presenting symptoms in IBS, particularly in women. Bloating is caused by excessive intestinal gas production. In a few cases, especially those who eat fast, belch and bloat very quickly, swallowing of air is the problem. This is usually obvious to the doctor although not well recognised. Most bloating, however, comes from gas production lower down the gut at the end of the small intestine and, in particular, in the colon. Here there are huge numbers of bacteria, some of which are expert at fermenting plant fibres into gas (including hydrogen, methane, carbon dioxide and hydrogen sulphide). Constipation often accompanies bloating – stool is composed mainly of bacteria so slow passage of stool around a long colon is going to be a perfect recipe for fermentation and therefore bloating and gas. Diets which reduce this are those that reduce wheat and insoluble fibres and fermentable vegetables such as broccoli, greens and beans (pulses). These are, of course, the very foods that we are persuaded to eat in a healthy diet so advice to remove them comes as a surprise. It is, however, often very successful. The low FODMAP diet is a more comprehensive diet removing fermentable carbohydrates and is perhaps the most successful diet in IBS. The dietitians at London Bridge Hospital are trained in the use of this and other diets and referral to see a Dietitian is therefore a common outcome after a diagnosis of IBS has been established. 

Breath testing

Breath testing is commonly used in the assessment of IBS symptoms (and occasionally in other patients eg in Crohn’s disease). The tests are designed to detect two specific carbohydrate intolerances – lactose and fructose maldigestion, and to look for evidence of small intestinal bacterial overgrowth (SIBO), either using lactulose, glucose or both as substrates for the test. The test involves ingesting a specified amount of the substrate solution (lactose, fructose, lactulose or glucose) and then measurement of hydrogen are taken from exhaled breath over the next 2-3 hours. Hydrogen is one of the products of carbohydrate fermentation in the gut which is absorbed into the blood, travels to the lungs and comes out in the breath. It is therefore a rather convenient and non-invasive way of assessing symptoms such as bloating and diarrhoea that might arise from abnormal gut fermentation. The results can then be used to tailor dietary treatment. If SIBO is present, antibiotics might be used in addition to diet. Other changes can also be determined by breath testing such as high methane production which correlates well with slow transit through the colon and hence constipation. 

Small intestinal bacterial overgrowth (SIBO)

SIBO is not a new concept but has only recently been proposed as a factor in certain cases of IBS. Traditionally, it occurred following surgery where parts of the gut were bypassed or, for example, in conditions where the nerves and hence motility of the gut were affected such as diabetes mellitus, amyloid, sceloderma etc.

In IBS, particularly those with diarrhoea (often smelly) and bloating, some patient appear to have evidence of bacteria in the small intestine as evidenced by an early rise in hydrogen following lactulose or glucose (on a breath test). Normally it takes 90-120 minutes for carbohydrate to reach the large intestine (colon) where bacteria are present in large numbers and hence a rise in hydrogen will occur at this time point. SIBO is suggested by a rise earlier than this, particularly if earlier than 60 minutes. 60-90 minutes may reflect rapid transit to through the small intestine. 

Direct sampling if the small intestine used to be undertaken but is not proven as a technique in IBS related SIBO (unlike classical SIBO described above). However, this might be a test undertaken in certain cases.

If present, SIBO can be treated with specific antibiotics. This could either be general antibiotics such as ciprofloxacin, co-amoxiclav or metronidazole and the newer, non-absorbable antibiotic, rifaximin. Other measures to help prevent recurrence include using low dose erythromycin to speed gut motility and clearance of bacteria and dietary approaches, especially the low FODMAP diet. Repeated antibiotics are sometimes needed as relapse after treatment is relatively common.

The use of antibiotics in this setting is controversial and should always be discussed carefully with the patient. Good antibiotic stewardship means that antibiotics should only be use where absolutely necessary and hence the evidence of SIBO must be compelling and, ideally, symptoms not responding to diet alone. 

Is Candida a real problem in IBS?

The answer to this is almost certainly yes. It is controversial and overstated but there is clearly a group of women (sometimes men too) who have a tendency to genital candida (thrush), perhaps other fungal infections eg nail or skin, and have bloating, sometimes diarrhoea but maybe constipation. Patients often have fatigue (sometimes referred to as a brain fog) and general symptoms. Foods containing yeast make the symptoms worse, such as bread, marmite, wine and beer (but not spirits) and sugar will also do the same as it promotes yeast driven fermentation. There is no proof of an overgrowth of candida (or other yeasts) in the gut but it makes sense and diets avoiding yeast and sugar can help (they are also very difficult as avoiding sugar leads to excessive tiredness). Antifungal drugs can also help (eg nystatin, itraconazole). 

Irritable bowel syndrome Treatment 

The approach to treating Irritable Bowel Syndrome at London Bridge Digestion

London Digestion consultants have built up an interest in treating Irritable bowel syndrome, partly through experience as Gastroenterologists for many years but also through a research interest in the bacterial flora of the intestine. The approach to IBS is holistic and individualised, particularly in difficult cases where a number of concerns and misconceptions may need to be addressed. Endoscopic investigations are very important (endoscopy / colonoscopy) to rule out other conditions such as Crohn’s disease, colitis, coeliac disease and bowel cancer but non-invasive tests such as stool and blood often suffice (especially in younger patients). We also offer breath tests to look for bacterial overgrowth and lactose intolerance, consultation with a specific GI dietitian, and referral where necessary for specific other treatments (for example CBT). 


In many cases IBS can be easily resolved – in others it can be very difficult but an individualised thorough approach usually gets most people substantially better and able to focus more on enjoying life and work rather than focussing on their stomach and bowel.

Specialists in this area
Prof Sanderson
Dr Dunn
Dr Berry