Irritable bowel syndrome or irritable diet?
Irritable bowel syndrome (IBS) is a very commonly diagnosed functional bowel disorder, with an estimated prevalence of about 20 per cent in the general population. As it causes gastrointestinal symptoms it is little wonder that many patients consider that what they are putting into the 'top end' (food) is the cause of their ailments.
Indeed, various studies have indicated that anywhere between 20 and 55 per cent of IBS sufferers attribute their symptoms to adverse food reactions. It is estimated that genuine adverse reactions to food occur in only 3-5 per cent of the population as a whole, and therefore it is clear that in many IBS patients there are alternative explanations for the symptoms.
Adverse food reactions
Diet can lead to gastrointestinal symptoms, either through a genuine hypersensitivity reaction (allergy) or due to the much more nebulous concept of food intolerance.
· Food hypersensitivity/allergy
This is an IgE-mediated immunological reaction to food triggered by the release of inflammatory mediators in response to food allergens. It can either be immediate (minutes) or delayed (hours). The former is usually dramatic and obvious (such as nut allergy) and there is seldom any diagnostic doubt. But the latter can cause symptoms similar to IBS, such as bloating and abdominal discomfort, and this can lead to diagnostic uncertainty.
These reactions can be detected by IgE RAST tests to various food allergens. In some studies up to 50 per cent of IBS patients have positive RAST tests to one or more food antigens. But excluding the positive foods often leads to little symptomatic benefit, thereby calling into question the clinical relevance of positive RAST tests; as a result they are seldom used by gastroenterologists.
Some independent food allergists or nutritionists test for IgG levels to foods. IgG is raised to most foods we eat and a higher level simply reflects those foods we eat the most. There is no evidence linking raised IgG levels to clinical symptomatology whatsoever.
Overall, food allergy testing is not widely available on the NHS, not least due to the paucity of allergists, and the advice offered by alternative sector professionals is invariably of dubious worth. On the whole, genuine food allergies in adults are rare and, in the big picture of functional bowel disease, a very niche diagnosis. As a gastroenterologist I would only consider arranging RAST tests when the suspicion of food hypersensitivity was high and the need for a definitive diagnosis necessary.
· Food intolerance This term encompasses non-immunologically mediated adverse reactions to food, which resolve following dietary manipulation and are reproduced by food challenge. This includes direct effects of pharmacologically active constituents of foodstuffs (tyramine in cheese, caffeine in coffee) and enzyme deficiencies such as lactose intolerance.
Lactose intolerance is probably the most common and affects about 5 per cent of the UK population. Other common food intolerances are to wheat, fish, tomato, apple, citrus fruits and onions.
Lactose intolerance fortunately is easily diagnosable with a breath test, which is more than can be said for virtually all other suspected food intolerances and herein lies one of the biggest problems in IBS management. How do you prove or disprove to the (often convinced) patient that a food or foods are the cause of their GI symptoms?
The 'difficult' patient
The more common scenario is the patient with intractable symptoms convinced that something in their diet is causing their problems. How can such a situation be resolved? First, of course, the patient may be right, and therefore before the idea is completely dismissed it should be considered along the lines suggested above.
But it is more likely they are incorrect. What they may describe is urgency, diarrhoea or bloating whenever or shortly after they eat. This will make them think back to the last meal, identify whatever they ate and then avoid it. This will probably be acceptable for a little while until the next bout, when they will identify another food and avoid that as well. This can go on and on, resulting in a diet that can end up nutritionally deficient.
What this illustrates, of course, is an exaggerated gastrocolic response (the increase in small and large bowel motility in response to gastric filling) which is happening as a result of eating per se, rather than due to an adverse reaction to a particular food.
What can then compound the difficulties is when the patient says: 'Every time I eat this food I get problems therefore it must be the cause.' The difficulty here is that whenever they contemplate and attempt to eat the particular food there will be a lot of anxiety, and this factor will bring on the symptoms in its own right. But this will usually not be appreciated by the patient, whose opinion will only get further entrenched, and any suggestion that anxiety/psychological overlay may be relevant is either met with anger or falls on deaf ears.
The placebo response is a very useful concept and can work in up to 40 per cent of patients for any therapeutic modality tried in IBS, including food exclusion. It could, therefore, be very reasonably argued that if a patient is feeling better, even if only courtesy of a placebo response, then rather than questioning the reasons for such an improvement we should be delighted especially if management is proving difficult. This is fine as long as the diet is nutritionally adequate, but usually the story does not end there. When the response is due to placebo effect, symptoms inevitably return, leading to even greater demands from the patient.
There will always be situations where it is quite clear that no amount of persuasion will change a patient's view and then a formal, dietitian-led food exclusion and reintroduction diet can be very helpful. Here the diet is pared down to a bare minimum (rice-based) and gradually different foods are reintroduced. If no reaction occurs then the next food is added in. If there is a reaction then that food is withdrawn and reintroduced again more slowly. These diets, done properly, take many months to complete and a huge amount of willpower on the part of the patient. In my experience, few patients manage to last the course and it is therefore not an approach I use very often.
If a food is identified then the only advice that can be given is that it should be avoided. But coming up with an answer the patient can identify with can lead to better symptom toleration and a considerable easing up of pressure on medical services from that individual. Alternatively, if no answer is forthcoming, the patient may at least feel the issue has been looked into properly and then may be more amenable to suggestions of other mechanisms, such as psychological issues. Either way, food exclusion
diets do most certainly have their place.
IBS is difficult to manage successfully. Each patient will have a unique set of symptoms and circumstances (clinical and personal), an individualised way of coping (or not), and their own individual psyche. No one case is the same as the next, and this means management has to be tailored individually. It is not surprising, when faced with a complex interplay of many factors, that in situations of more entrenched difficulties simple remedies, be they medication or dietary manipulation, are rarely effective.
Sadly many gastroenterologists, as well as GPs, regard these patient as 'heartsink' and do not give them sufficient time or attention to properly explore the relevant issues. The reason for any referral is that both patient and GP need help, and simply ruling out organic pathology is usually not good enough.
An approach to the IBS patient
· The clinical picture is important. Food hypersensitivity or intolerance is much more likely to cause bloating and diarrhoea than constipation or pain.
· If symptoms have been ongoing for many years, the patient has normally been able to identify the culprit, if there is one.
· Where symptoms have other 'drivers' anxiety or stress a food aetiology is unlikely.
· In terms of investigations, an anti-endomysial antibody (sensitive marker for coeliac disease, especially if the clinical picture is diarrhoea-predominant), and a lactose breath test (if there is any suggestion of a link with dairy products) are useful.
· A symptom and diet diary can be helpful, although it is important not to make the patient too obsessive about their symptoms.
· Fibre and fibre-containing foods (for example green vegetables such as broccoli and cabbage) may lead to bloating.
· Insufficient fibre may exacerbate constipation.
· Fluid intake (non-fizzy drinks) of at least two litres per day is needed.
· Irregular meal times can be a problem, especially for shift workers.
· If the more standard medical approaches to symptom relief are not proving terribly beneficial, patients can try their own selective exclusion diets, tackling the more commonly seen intolerances, such as
dairy products, wheat
· As a general principle, supported by 15 years' experience, if no clear pattern has emerged by this point it is unlikely food hypersensitivity or intolerance is involved and I would usually not
pursue this matter any further. If a very obvious culprit has been
identified, and avoidance leads to symptom improvement or even resolution, then no further action is required other than continued avoidance. If genuine doubt remains then a formal food exclusion diet may be useful.