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Food Allergies And Irritable Bowel Syndrome

Food Allergies And Irritable Bowel Syndrome

Food Allergies And Irritable Bowel Syndrome


Many people are very willing to attribute all their digestive and irritable bowel problems to their diet. Sometimes they are right. But at other times, people can become totally obsessed with avoiding food that they think has previously upset them, refusing to accept continuing symptoms as evidence that their strategy has failed. If only someone would tell them what to eat and what not to eat, they feel all would be well. By contrast, doctors are mostly very sceptical about dietary interventions for irritable bowel, and they may show little interest in people’s diet and offer little or no advice in this area. But both these extremes are unjustified. The purpose of this chapter is to describe how certain food allergies or intolerances can produce irritable bowel syndrome (IBS)-type symptoms, and which diets are worth trying.

Why are doctors sceptical about dietary interventions for irritable bowel syndrome?

Doctors receive little training in nutrition and dietetics. They may see their role predominantly in terms of diagnosing and treating illnesses that have more ready cures. After diagnosing irritable bowel syndrome, the only dietary intervention that some doctors know of is to increase the fibre intake. But more fibre only helps a minority of irritable bowel syndrome patients, and the failure of this approach is taken as evidence against a dietary strategy. Moreover, patients readily tell their doctors of dietary changes that they have tried, and since people go to their doctors to report symptoms, the failure of their own dietary manipulations is taken as further proof that dietary interventions fail. Indeed, doctors can be very sceptical about anyone’s ability to undertake any lifestyle change, however important it might be.

Finally, doctors like to use standard treatments that apply to most people with a given condition. This isn’t just because it’s easier and quicker to prescribe a treatment than to individualise it. By recommending ‘standard’ treatments, we get a feeling for how well they work and for the possible side effects. Otherwise it becomes more difficult to judge whether any apparent detrimental effect is a consequence of the treatment or of the condition being treated. With this knowledge, doctors can become very good at individualising drug-based treatments.

When it comes to dietary treatments, it becomes far more difficult. There is a lack of knowledge in general, as well as training, particularly among doctors. But more than that, there is a huge variability between people in their response to food. This means that there is no ‘irritable bowel syndrome diet’. If a dietary approach is to be successful, the diet needs to be individualised. This can be very time-consuming, and there is no guarantee of success.

What is the difference between a food allergy and a food intolerance?

Some people have unpleasant reactions to specific foods that most people find harmless. In an allergy, this adverse reaction is mediated by the immune system. In other words, the cells and antibodies designed to protect us against infection mistakenly target specific foods or components of foods. The symptoms are caused by the reaction of the immune system rather than by the food itself. A minute amount of food to which an individual is allergic can elicit a dramatic, even life-threatening, reaction. Chemicals secreted into the bloodstream by cells of the immune system are spread throughout the body, causing symptoms such as swelling of the face, difficulty breathing and a fall in blood pressure. The reaction can be severe enough for an individual to collapse to the floor, and may be lifethreatening. Fortunately, such reactions are rare.

By contrast, a food intolerance does not involve the immune system. The adverse reaction to the food is caused by the direct chemical effect of the food or its components. Such reactions can be divided into three main groups. First is toxic or pharmacological. That is an expected reaction due to the known action of the food. For example, eating large amounts of rhubarb will cause loose stools in most people because rhubarb contains a natural laxative. Second, some people have a deficiency in their metabolism that leads them to react adversely to foods that are harmless to most people. Lactose or dairy food intolerance due to the absence of the enzyme lactase is an example of this. Third, some people react adversely to food, but the mechanism is unknown.

Does it matter if it’s a food allergy or a food intolerance?

With a food allergy, the reaction can occur following a minute dose because it is amplified by the immune system. With a food intolerance, the extent of the reaction depends on the dose, so small amounts may be tolerated.

If my irritable bowel syndrome is caused by a food allergy, does it matter for my longterm health if the allergy isn’t identified?

Allergies that affect the respiratory system or cause facial swelling that may interfere with breathing can be life-threatening. People have died from nut allergies. But no one has died from irritable bowel syndrome. As far as we know, food allergies and intolerances that produce irritable bowel syndrome-type symptoms do not cause any long-term damage. The only exception to this is coeliac disease, which has been associated with an increased risk of cancer and osteoporosis if it goes untreated.

Last night my wife cooked cabbage mixed with bacon and spices. It was delicious, but in the night and today, I’ve had terrible pains in my lower abdomen. The pain has been coming and going in spasms, I’ve felt bloated, there has been a lot of noise from my tummy, and my stools have been loose. Do I have irritable bowel syndrome, or am I intolerant of cabbage?

It may be neither. The most likely explanation is that your bowel is just reacting normally to a quantity of fibre or spice that it isn’t used to. Fibre will bulk up your stool, holding water and gas in your bowel, and thus distending it. The spices may have stimulated more muscle activity. The result is bloating, spasm and loose stools. If you continue to eat this food, your bowel will probably adjust with time. For now, try smaller quantities.

I can understand how you could attribute your symptoms to the cabbage. My point is that the simpler explanation above is more likely. You may well have experienced similar symptoms in the past with other foods. If you attempt to avoid them all, your quality of life will suffer. Remember it may have been the quantity of cabbage that caused the problem, or it may have been the spices, or perhaps it was something else entirely.


Foods Commonly Implicated With Irritable Bowel Syndrome

Which foods are most commonly involved in food allergy? And what symptoms do they cause?

Only eight foods or food groups are responsible for the vast majority of antibody-mediated food allergies. They mostly cause reactions affecting the entire body and are thus easily distinguished from irritable bowel syndrome. In each case, antibodies called IgE antibodies are produced to react with a specific constituent of the food. The antibodies are present on the surface of specialised immune cells in the gut called mast cells. These cells make a variety of chemicals such as histamine that they store in granules within the cell. When an IgE antibody on a mast cell reacts with its specific food, the mast cell releases its granules. The chemicals released from the granules are then distributed in the bloodstream.

The reaction these chemicals produce often affects the whole body more than the gut. Swelling, especially of the face and lips, is caused by leakage of fluid from the blood vessels. The blood pressure falls because fluid has been lost from the circulation. Breathing can be difficult because of muscle spasm in the airways and fluid leakage into the lungs. In the skin, a localised leakage of fluid can cause an itchy rash called urticaria (hives). The gut responds with diarrhoea, vomiting, nausea and pain.

The severity of the reaction depends on how sensitive the individual is to the food and how much of the food has been taken. The reaction can be treated with antihistamines and adrenaline (epinephrine). In some cases, it can be prevented by a drug called sodium cromoglicate, which acts to stabilise mast cells and reduce their propensity to release their granules.

These food allergies are clearly nothing to do with irritable bowel syndrome.



The Food Groups Causing Antibody-mediated Food Allergy

Food Group




Cows milk

Up to 2% of infants are affected by this. Most become tolerant to cows milk by 2years of age.


This usually affects only infants and children, is usually mild and is usually outgrown.


This mostly affects infants and children but has also been seen in adults.


Antibody-mediated wheat allergy is different from coeliac disease. It is usually mild and predominantly affects infants and children.


The peanut is not a nut but a member of the legume family. Peanut allergy is claimed to affect up to 0.5% of the population. In contrast to other allergies that also begin in childhood, it is often not outgrown.


This is less common than peanut allergy. It can be outgrown, but it has been seen in adults.

(shrimps,crab,lobster crayfish etc)

In contrast to other allergies, this one seems to be more common in adults than children. It is also more common in Asia.

Tree nuts
(almond, hazel, walnut, brazil, cashew, pistachio, etc)

Tree nut allergy may affect as many as 0.4% of the population. as with peanut allergy, it is not outgrown.


Which foods are the most frequently implicated in irritable bowel syndrome?

The most commonly incriminated foods are milk, eggs, nuts, wheat and fish.


Milk And Dairy Products

Milk is an important nutrient, providing almost half the calcium of the average British diet. It is also rich in vitamins and other minerals. Semi-skimmed milk is usually less than 2% fat. A daily glass of semiskimmed milk provides a 6-year-old with all the vitamin B12, around half of the calcium, phosphorus and vitamin B2, about one third of the protein, potassium and iodine, and around one tenth of the vitamin A, vitamin B1, niacin, vitamin B6, folate, magnesium and zinc that he or she needs each day.

A few people are allergic to milk. More people may have lactose intolerance.

What’s the difference between cows’ milk allergy and lactose intolerance?

Cows’ milk allergy is caused by an immune reaction to milk proteins. In lactose intolerance, there is no immune reaction; the symptoms are instead caused by a failure to digest lactose (the sugar in milk).

Cows’ milk allergy occurs in up to 2% of infants, usually within the first 3 months of life. Some infants fed entirely on breast milk can become exquisitely sensitive to cows’ milk, but in most the reaction is mild. The major symptoms are vomiting, diarrhoea and abdominal pain occurring within minutes to an hour of the milk being given.

In a few cases, the reaction is more serious, with facial swelling, wheezing and a fall in blood pressure. This is called anaphylaxis, and it occurs because immune cells in the gut carrying antibodies against the milk proteins have released large amounts of histamine and other chemicals into the bloodstream. These chemicals cause fluid to leak out of the blood vessels, causing swelling and a fall in blood pressure. At the same time, they can cause spasm of muscle in the airways of the lung, leading to wheezing and breathlessness. Fortunately, anaphylaxis is rare. The symptoms of cows’ milk allergybecome less severe with age, and most children are tolerant of milk products by 2 years of age.

Lactose intolerance occurs because most humans lose some of the ability to digest lactose in adulthood. Lactose is the sugar in dairy products. If it is undigested, it passes through the small bowel into the large bowel where, by holding water within the bowel, it causes diarrhoea. Some of the lactose is digested by bacteria to produce gas. The immune system is not involved, and the severity of the symptoms depends on the amount of lactose ingested. Most lactoseintolerant individuals can tolerate small amounts of lactose.



Probably the most frequent dietary advice given to people with irritable bowel syndrome is to increase the amount of fibre in their diet. They are exhorted to eat wholemeal bread, bran, wheat crackers and other high-fibre foods. Yet one of the foods most commonly reported as exacerbating irritable bowel syndrome is wheat. This contradiction shows why people with irritable bowel syndrome should take all dietary advice from non-dietitians with a pinch of salt.

I know that coeliac disease is related to wheat. Is coeliac disease a food allergy?

Yes, but in contrast to the food allergies described above, the immune reaction is not mediated by antibodies, but by cells localised to the small bowel. In coeliac disease, there is an abnormal immune response to gliadin, a constituent of wheat, rye and barley. This results in inflammation and damage to the lining of the small bowel. Symptoms arise because food cannot be properly digested and absorbed. Although antibodies to gliadin are present in the blood – and this is used as a screening test for coeliac disease – the antibodies are not involved in the disease process itself.

What is the difference between wheat intolerance and coeliac disease?

Some people with irritable bowel syndrome feel much better on a wheat-free diet. When tested, they do not have coeliac disease, and other than provoking their irritable bowel syndrome symptoms, wheat does them no harm. The mechanism behind this effect is unknown. It may be something in the wheat that they are unable to digest, or which bacteria in their bowel readily ferment to gas; or it may simply be that wheat-free diets include less fibre. In any case, it is reasonable to continue a wheat-free diet if your irritable bowel syndrome responds to it, but the diet does not have to be strict or indefinite. By contrast, the gluten-free diet in coeliac disease has to continue indefinitely and be strict. Otherwise, the reaction to gliadin will recur and persist.



What are lectins?

Lectins are naturally occurring plant proteins that are able to bind carbohydrate molecules. After they have been eaten and absorbed, the lectins can combine with carbohydrate molecules on the surface of cells, causing them to stick together. The damage can be extreme. For example, the poison ricin is a lectin derived from the castor bean, and as little as 500 µg can kill an adult.

Over 100 different lectins have been identified in foods, and it is tempting to speculate that they have some effect on our health and well-being. However, it is also possible that some plant lectins actually protect against some cancers, whereas others may cause disease. Some foods commonly implicated in irritable bowel syndrome have been shown to contain lectins so this has made people interested in their role in irritable bowel syndrome.

So which foods contain lectins?

Lectins are present in plant foods, particularly in the peel. The table below gives a list (albeit an incomplete one) of common lectincontaining foods.

Foods Containg Lectins






Broad beans




Castor (oil) beans








Green peas












Red kidney beans




Runner beans




Soya beans





Does anything happen to lectins during cooking?

Most lectins in foods are deactivated and broken down by cooking. However, some lectins are remarkably heat resistant, including those of wheat, tomato, carrot, corn, rice, peanut and banana. The increasing popularity of diets containing raw and relatively unprocessed foods probably means that some people are consuming more lectins now than at any time in human evolution. The ‘stoneage diet’ (see later in the section) is low in lectins, although it was not designed with lectins in mind.

Do lectins contribute to irritable bowel syndrome?

Some people with irritable bowel syndrome are much better when they avoid raw vegetables and fruit, or wheat. It is tempting to suppose that this improvement is a consequence of ingesting fewer lectins, but at present this is merely a guess.


Other food constituents that can have effects contributing to irritable bowel syndrome

What does dietary fibre do?

Dietary fibre is indigestible plant carbohydrate (primarily cellulose pectins and lignins from the plant cell wall). It passes through the small bowel undigested to the large bowel, where bacteria partially metabolise it into gas, fluid and short-chain fatty acids. The short-chain fatty acids are absorbed by the large bowel and form an important nutrient. Most of the rest passes through in the stool along with water and gas trapped within it, and the bacteria living on it. Fibre therefore produces a softer, wetter, bulkier stool that is easier to pass.

Whenever I eat anything with a high fibre content, I get diarrhoea. Could I be intolerant or allergic to fibre?

You can call it an intolerance if you like, but actually looser stools are a natural consequence of eating more fibre, so there’s nothing wrong.

What’s the effect of caffeine?

Caffeine is a constituent of coffee, tea, cola and chocolate. It’s thought to act by competing with the compound adenosine for its receptor on the cell walls. Adenosine is continually present in small amounts in the fluid surrounding all the cells in the body. It reacts with a receptor on the cell surface and acts to ‘dampen down’ cell activity. By competing with adenosine, caffeine acts as a stimulant throughout the body, producing a multitude of effects to a greater or lesser extent in different people.

Caffeine is a drug of addiction. Withdrawal symptoms include irritability, fatigue and headache.

The Effects Of Caffeine


Physiological effects

Possible adverse effects with high doses in susceptible individuals


Decreased fatigue
Elevated mood

Agitation and nervousness

Heart and circulation

Increased heart rate
Higher blood pressure

Abnormal heart rhythms
High blood pressure

Gastrointestinal system

Increased acid production
Decreased pressure in the lower oesophagael sphincter, the muscle that stops the stomach contents regurgitating
Increased water and salt secretion by the bowel
Increased bowel muscle activity

Dyspepsia (indigestion)


More urine being produced (diuresis)

Mild dehydration


What is the effect of salt?

In the long term, excess salt in the diet may contribute to cardio – vascular disease. However, eating a meal with much more salt than you are used to can cause more immediate symptoms such as headache, thirst and bloating. These symptoms are probably due to fluid shifts within the body, initially from the bloodstream into the gut, and then from the rest of the body into the bloodstream.

Salt is sodium chloride, and it’s the sodium that is the active component. In a Chinese meal, large amounts of sodium can be eaten as monosodium glutamate. It is therefore not uncommon to feel thirsty and bloated after a Chinese take-away.

What is monosodium glutamate, and what effects does it have?

Monosodium glutamate is the sodium salt of glutamic acid. Glutamate is a naturally occurring amino acid (a basic building block of protein) that is found in nearly all foods, especially highprotein foods such as dairy products, meat and fish, and in many vegetables. Foods often used for their flavouring properties, such as mushrooms and tomatoes, have high levels of naturally occurring glutamate.

Monosodium glutamate added to foods has a flavouring function similar to the glutamate that occurs naturally in foods. It acts as a flavour enhancer and adds a fifth taste, called ‘umami’, which is best described as a savoury, broth-like or meaty taste. In the European Union, monosodium glutamate is classified as a food additive (E621), and regulations are in place to determine how and when it can be added to foods. Typically, monosodium glutamate is added to savoury prepared and processed foods such as frozen foods, spice mixes, canned and dry soups, salad dressings and meat- or fish-based products. In some countries, it is used as a table-top seasoning.

Some people are sensitive to monosodium glutamate and suffer from what has been termed the ‘Chinese restaurant syndrome’. About 10–20 minutes after a meal containing monosodium glutamate, they develop chest pain, flushing of the face and headache. The mechanism behind this reaction is unknown. The chest pain is not due to heart disease but is more likely to be caused by spasm in the oesophagus. Although this reaction has been associated withfood containing large amounts of monosodium glutamate, such as Chinese food, the monosodium glutamate itself may not always be to blame as such foods also contain histamine, which produces similar reactions in the body during allergic reactions.

If histamine may be a culprit, which foods contain large amounts of histamine?

Histamine is one of the compounds released during an allergic reaction. It can have effects throughout the body that depend on where and how much histamine has been released. In a food allergy, histamine may be released from mast cells in the gut.

Interestingly, however, some foods can contain significant amounts of histamine, which can then be absorbed from the gut. If you have enough of them, a typical histamine reaction can occur, mimicking an allergic reaction. The symptoms may include urticaria (an itchy raised transient rash, also called hives), gastrointestinal symptoms such as abdominal pain, diarrhoea, nausea and vomiting, and facial flushing. Why some people are affected and others not probably relates to the variation in our ability to break down histamine before it is absorbed, and after it has been absorbed when it passes through the liver. The effects of histamine can be prevented by antihistamine tablets, which can be purchased over the counter.

Foods containing considerable amounts of histamine are yeast extracts, fish, chocolate, alcoholic drinks, and fermented products such as cheese, soy products, sauerkraut and processed meat. Histamine is produced in food by bacteria and yeasts. As a result, food that is overripe or decaying, especially fish and meat, may have very high quantities of histamine. Marmite has a particularly high concentration of histamine.

Scromboid poisoning is a severe reaction occurring 5 minutes to an hour after eating food containing large amounts of histamine, usually rotting tuna or mackerel. Symptoms are flushing, headache, dizziness, burning of the mouth and throat, nausea, vomiting, diarrhoea and palpitations.

What is the effect of spicy foods?

The typical effect of eating a highly spiced meal is an immediate feeling of fullness that can last for hours or even through to the next day. This may be because highly spiced food moves through the small intestine more slowly, as one study has shown. In spite of this, 60% of the people studied experienced mild diarrhoea, implying that spicy foods had opposite effects on the small and large intestines. Slowing down of the small intestine leads to bloating, while speeding up of the large bowel means that its contents are expelled as diarrhoea. There is currently no explanation for the effects of spicy foods on the gut. Many people with irritable bowel syndrome find that their symptoms are exacerbated and take care to avoid spicy meals.

What is the effect of alcohol?

Alcohol can certainly cause and exacerbate gastrointestinal symptoms. It is a common cause of heartburn and other indigestion pains as well as diarrhoea. It is also possible that an individual is sensitive to the food from which the alcohol was derived rather than the alcohol itself. Interestingly, alcohol may also amplify the food intolerance response. So a meal containing wheat, for example, may only cause a problem if it is accompanied by alcohol. This can cause confusion when testing foods, but it may also be readily apparent from a food diary.

What about meat?

Meat, especially beef, gained a bad reputation for health when diets high in animal fat were associated with an increased risk of cardiovascular disease, strokes and heart attacks. But when trimmed of visible fat, beef is actually usually less than 10% fat. It is also an excellent source of protein, iron, zinc and the B vitamins. When it comes to food allergy, meat barely gets a mention; compared with other foods, meat intolerance is uncommon.

Meat contains virtually no fibre. Consequently, if you have constipation- predominant irritable bowel syndrome, a diet high in meat may make you worse. Conversely, people with diarrhoea-predominant irritable bowel syndrome may do better with more meat and fewer vegetables.

What about a vegetarian diet?

The vegetarian diet is inevitably high in fibre. So bloating, wind and diarrhoea will tend to be worse.


A Dietary Approach To Irritable Bowel Syndrome

What is an elimination diet?

An elimination diet is one in which specific foods or groups of foods are totally avoided. If a person’s symptoms are due to specific food allergy or intolerance, avoiding that particular food should resolve the symptoms within 4–7 days. Reintroducing the food will lead to a recurrence of the symptoms, confirming the diagnosis. Elimination diets can therefore be used to diagnose and treat food allergies and intolerances. But in practice it isn’t as easy as that.

When is it worth trying an elimination diet?

Food allergies and intolerances generally do not cause constipation, so it’s only worth considering an elimination diet if diarrhoea is a predominant symptom.

How do you decide on which food to avoid?

There are a number of possible approaches.

You can avoid specific foods because you have associated them with symptoms. Keep a detailed food diary to guide you in choosing which foods to avoid.

You can avoid a few certain foods because they are known to commonly cause symptoms.

You can try a very restricted diet designed to be free of the more commonly non-tolerated foods. Once the symptoms have resolved, other foods can be reintroduced (called a food challenge) in the hope of identifying which specific food or foods are responsible for the symptoms.

How does a food diary help?

A diary detailing food consumed, along with any symptoms, may show which foods are associated with which symptoms, guiding you in your choice of foods to eliminate from your diet. It may also show that there is no connection between your diet and your symptoms. Ideally, you should detail all food and drink consumed, bowel movements, mood, stressful events, medications, exercise and symptoms. But even a simple list of just food and drink may be better than relying on memory.

You should keep a detailed food diary for at least 5 days, including a weekend, and ideally for longer. A simple food diary can be a few sheets of paper or a notebook. You can then extra add columns for any information that you feel is relevant.

I’ve tried to avoid foods that seem to be associated with my symptoms, but my symptoms keep recurring. What can I do?

Most people approaching a physician or dietitian for help will already have tried to avoid foods that they believe are associated with their symptoms. Even if they are still avoiding certain foods, the strategy has failed to completely resolve their problem.

There may be a number of possible explanations for this failure. First, we all eat mixed meals, so it’s very difficult to know which specific ingredient caused the problem. You may have eliminated the wrong food. A detailed food and symptom diary may suggest which foods to try avoiding.

Second, the food to be avoided may be widely used in the food industry and may thus be inadvertently ingested. Eggs, wheat and milk are examples of foods to which people are frequently intolerant or allergic but which are used in a huge range of products and may not be included in the ingredient list. For example, egg white or milk is used in clarifying wine.

Third, not all the foods causing the problem have been eliminated. And finally, the problem may not actually be a food allergy or intolerance.

I’ve got diarrhoea-predominant irritable bowel syndrome. Which foods or groups of foods is it worth trying to avoid?

There are several relatively straightforward dietary manipulations that are worth trying.

A lactose-free diet – Avoid dairy products, including milk, butter, cheese and yoghurt. If you have lactose intolerance, there should be a dramatic improvement within a week. You can then reintroduce lactose to confirm the diagnosis. Even if the diagnosis is confirmed by re-testing, you may still be able tolerate small amounts of dairy products – yoghurt and hard cheese contain relatively little lactose. In addition, lactose tolerance may return in time so it’s worth re-testing every few weeks or months.

A fructose- and/or sorbitol-free diet – These sugars can be difficult to digest, and diarrhoea occurs in some people if they are ingested in large quantities. Foods containing significant quantities of fructose are listed in the table below.

Fructose In Food



Fructose content
(g per 100g serving)









Cola drinks








Sorbitol, a polyol (a sugar alcohol), is a bulk sweetener found in numerous food products, including sugar-free sweets, chewing gums, frozen desserts and baked goods. It is also used as a base for medical products. Sorbitol is about 60% as sweet as sucrose with one third fewer calories. It has a sweet, cool and pleasant taste. Sorbitol is slowly converted to fructose in the intestine and may be poorly absorbed.

Sorbitol is known to cause diarrhoea in doses of more than 50 g a day. But some people may be more sensitive and suffer from diarrhoea and bloating at far smaller daily doses. Unfortunately, food labels may not state the quantity of sorbitol contained. In fact, despite the inclusion of sorbitol, the label may state that there is no added sugar. A sugar-free chewing gum probably contains 1g of sorbitol per stick of gum, and some ice creams may contain much more. If you eat a significant quantity of ‘sugar-free’ products, it is very easy to ingest a sufficient quantity of sorbitol to produce diarrhoea.

A caffeine-free diet – A high intake of caffeine not only stimulates the gut but may increase nervous tension that could increase gut irritability.

A wheat-free diet – Some people with irritable bowel syndrome, especially those in whom diarrhoea and bloating are the main symptoms, feel better on a wheatfree diet even if they do not have coeliac disease.

We do not know why this should be, but there are several possibilities. Wheat fibre is one of the more laxative types of dietary fibre, so it is hardly surprising that eating less of it will improve diarrhoea-predominant problems. However, wheat may also be involved directly in food allergies, and it is in addition a source of dietary lectins (see earlier in the section).

An alcohol-free diet – A high intake of alcohol will certainly damage and irritate the gut, causing nausea, pain and diarrhoea. In severe cases, it can take 4 weeks of abstinence to resolve.

I haven’t had any success with simple dietary manipulations. Now I want to try a more stringent elimination diet to see if this will improve my symptoms. What kinds of diet are available?

There are many suggested diets. Some possibilities are detailed in the tables and lists below. The rationale for such diets is twofold. First, trying to avoid particular foods can be difficult because many food products contain a mixture of ingredients. So diets that tell people what to eat rather than what not to eat are simpler to apply. Second, the more stringent the diet, the better the chance that the offending food or foods have been eliminated.

Once a symptom-free state has been established, it is possible to reintroduce foods one at a time (food challenge), with the aim of establishing which food or foods cause the problem.


The wheat, milk and egg-free diet

Wheat, milk and eggs are three common allergens that frequently come together in prepared food. So although it is possible to avoid one or other of these foods, some specialists recommend a diet that excludes all three.

Avoiding wheat – Foods with wheat may be labelled as containing any of the following: wheat grain, starch, flour, bran and farina. People with wheat intolerance or allergy should also avoid ‘gluten-free’ wheat starch as it is probably not the gluten to which they are reacting.

Baking powder, salad dressings, sausages, many gravies and many alcoholic drinks, including beer, lager and whisky, are also culprits. Even so-called ‘pure’ rye flour may contain wheat as the seeds are frequently contaminated. In any case, people who react to wheat are likely also to react to rye and barley.

Avoiding milk – Foods may be clearly labelled as containing milk or dairy products, but it should be noted that casein, caseinate, lactose and whey are also derived from milk. Even ‘non-dairy’ milk or cream substitutes may contain one of these derivatives. Many medicines contain some lactose as a base, as do artificial sweeteners.

Some foods should be assumed to contain milk or milk derivatives unless otherwise stated. These include non-dairy ice cream, chocolate and other sweets, margarine and bread.

Avoiding eggs – Egg derivatives include vitellin, ovovitellin, livetine, ovomucin, ovomucoid and albumin. They are used in many common foods, including cakes, biscuits, bread, croissants, pastry, meringues, icing and sausages. Egg is also used in the production of wine, some instant coffee and root beer.


The stone-age diet

The stone-age diet looks back to an age before dairy products and grain became a staple part of our diet. Fossil evidence from groups of hunter-gatherers suggests that the daily diet was derived primarily from animal-based foods. In particular, our ancestors enjoyed animal organ meats like liver, kidney and brain – meat-foods that are extremely rich sources of nutrition. Stone-age humans did not consume much dairy food, nor did they eat high-carbohydrate foods such as legumes or yeast-containing foods, or cereal grains. It is said to be free of the more commonly non-tolerated foods and also contains fewer lectins.

Foods allowed in the stone-age diet.

Fresh or frozen meat – any kind

Fresh or frozen fish – any kind

Fresh or frozen poultry – any kind

Fresh vegetables – any kind (including sweet potato) but not potato, tomato or soya

Fresh fruit – any kind except citrus fruits

Grain – rice, rice cakes, noddles

Grain substitute – buckwheat, quinoa

Drinks – spring water, additive-free juices of allowed fruits, herb and fruit teas

Seasoning – sea salt, fresh pepper, fresh herbs

Nuts – allowed unless there is a known allergy

Oils – olive oil, sunflower oil, safflower oil



Foods not allowed are:

cereal grains

milk and all dairy products






citrus fruits (orange, lemon, grapefruit, etc.).

The diet can be changed if allergy or intolerance to one or other component is suspected.



The ‘few-foods’ diet

This diet provides a minimal set of foods thought to be the least likely to produce an allergic or intolerant response.

Are there any problems with elimination diets?

Many people who may benefit from the diet initially suffer withdrawal effects over the first few days of the elimination diet. Headache is the most common symptom, but nausea, diarrhoea, fatigue, aching limbs, weakness, agitation and depression can also occur. Withdrawal symptoms are likely to be worse in people who were accustomed to drinking significant quantities of coffee and alcohol. Food cravings may also occur and may be severe. It is worth making a note of the craved-for food as it may subsequently prove to be responsible for the original symptoms.

Elimination diets are only for short-term diagnostic use. They are unlikely to be nutritionally adequate in the long term. Once the original symptoms have been resolved, foods are sequentially reintroduced to establish which food or foods are the cause of the problem.

Foods allowed in the few-foods diet







Sweet potatoes





Cooked carrots

Safflower oil

Sea salt

Olive oil



How long should I continue an elimination diet before reintroducing foods?

If the original symptoms were occurring daily, you can begin to test foods as soon as they have cleared. Otherwise, you have to continue for sufficiently long to be sure that the symptoms have improved. If withdrawal symptoms occur, the diet should be continued until these have passed and there have been 2–3 days of freedom from symptoms.

How long should I try each newly introduced food for?

This depends on the symptoms you suspect have been caused by the food. Some reactions can occur within minutes. Others such as eczema or joint pains may take 2–3 days to appear. In general, gastrointestinal symptoms will take less than 8 hours to show up. In other words, if you suspect that milk gives you diarrhoea but don’t have diarrhoea for 8 hours after drinking a pint of milk, you can conclude that the milk is innocent. You can continue to drink milk and try another food.

In general, one new food is reintroduced every fourth day, initially in small amounts, and then in normal servings on the next two days. If no reactions are observed for three consecutive days, the food can be included freely in the diet. What if I still have symptoms despite a strict diet such as the stone-age diet or the few-foods diet? It is possible that you are inadvertently still eating a food to which you are sensitive. But it is probably more likely that your symptoms are not caused by a food intolerance or allergy. The process of eating and digesting, the function of your gut, or the signalling process between your gut and your brain may be at fault, but the problem is not related to a specific food or foods.

How effective is the dietary approach as a treatment for irritable bowel syndrome?

In some studies, almost half the people who complied with a highly restricted elimination diet responded. In other studies using similar methods, fewer than 1 in 6 people improved. Once the subjects had responded such that they had no, or minimal, symptoms, individual foods were reintroduced in order to identify the specific foods causing the symptoms. This is known as a food challenge. In general, people reporting diarrhoea were more frequently successful with this approach than were those with constipation.

How many foods are people with irritable bowel syndrome usually intolerant to?

There is great variability between individuals. In those who are studied, about a third have between two and five food intolerances, about a third are intolerant to 6–10 foods, and a third are intolerant of more than 10 foods. Only about 1 in 20 are intolerant of just one food.

Can antibody testing help determine which foods to eliminate?

Possibly. In one study, the presence in the blood of an antibody called IgG antibody to various foods was determined for each individual participating. For each person, two diets were devised – one excluding all the foods to which the person had antibodies, and another, called the sham diet. The sham diet eliminated the same number of foods as the true diet, but these were foods to which there were no antibodies. The researchers tried to make the sham diet as difficult to follow as the true diet by eliminating the same number of staple foods in each diet. All the people participating had irritable bowel syndrome. They were randomly allocated to follow a true or a sham diet, but they did not know which diet they were following. They continued the diet for 12 weeks and assessed the severity of their symptoms by completing a questionnaire.

The diets were difficult to follow, and almost a third of theparticipants in the study withdrew. But of those who continued the diet, either fully or partially, 28% improved on the true diet compared with 17% on the sham diet. About a third of individuals were able to adhere fully to the diet, and over half of these showed a significant improvement.

It is possible that testing for antibodies to food in the blood may be useful in determining which food to avoid. Such testing is not available on the NHS but is available commercially from Yorktest Laboratories (see the Appendix for details); it involves just a fingerprick blood sample.

Is there any alternative to an elimination diet for food allergy?

There is a drug called sodium cromoglicate that is thought to act by stabilising mast cells. These are the cells that react to the food allergen, releasing chemicals such as histamine, which cause the adverse reaction. Sodium cromoglicate is used in other allergic conditions such as asthma, and although it occasionally causes nausea, it is usually free of side effects and safe to take even in children. In one study, it was found to be as effective as an elimination diet, but this success has not been repeated. Unfortunately, sodium cromoglicate is not cheap – currently about £70 a month.

Are there any side effects from changing the diet?

Diets can affect our well-being. This is noticeable even to normal people when they eat a different diet on holiday. In the first few days, you can get withdrawal symptoms including irritability, fatigue and headache. Food cravings are common. Eating too little, especially eating too little carbohydrate, will result in ketone production from the fat stores. While this helps you to lose weight, ketones also cause nausea, headache, abdominal pain and fatigue.

If your new diet involves eating more fibre, then more bloating is almost inevitable in the first few days or even weeks. If your main problem is diarrhoea, more fibre may exacerbate it. Eating less fibre may help with bloating, but it may also contribute to constipation.

In the longer term, nutritional deficiencies are a worry. Iron deficiency is very common in vegetarians. People who avoid dairy products risk taking insufficient calcium in their diet. The longer we live, the more of a problem weak bones become.

Dieting can be socially restrictive and a terrible annoyance to the rest of the family. Keeping a detailed food diary, although possibly the most useful first step, can be enormously time-consuming, selfindulgent and the first step towards developing a food obsession. So if you keep one, keep it only until you have a result one way or the other.



A dietary approach to irritable bowel syndrome may work for some people some of the time, but opinions differ on how effective it is and what to try first. It is more likely to work in diarrhoea-predominant irritable bowel syndrome because constipation is unusual in food allergies and intolerances.

A dietary approach inevitably involves a lot of work, discipline and, most of all, experimentation. How much effort you wish to expend is your decision. Be aware of the huge variability between people, and be sceptical of ‘miracle’ diets. There is often variability for the same person too: what affects you today may not upset you tomorrow. This may be apparent from your food diary, and it implies that dietary manipulation will be unsuccessful. You may need to fall back on the famous saying by the American author Mark Twain, ‘Part of the secret of success in life is to eat what you like and let the food fight it out inside.‘



Food intolerance or allergy may be responsible for or exacerbate symptoms of irritable bowel syndrome.

People vary hugely in their response to specific foods.

People vary over time. What may upset you today may not upset you tomorrow, and vice versa.

Food allergies and intolerances generally do not cause constipation.

People may be intolerant or allergic to multiple foods.

Dietary interventions can be difficult and time-consuming, and there is no guarantee of success.

An allergy involves the immune system, which amplifies the reaction, so a very small amount of the offending food can produce a severe effect.

A food intolerance does not involve the immune system, and the effect of the offending food depends on how much of it is taken. Small amounts may be tolerated.

The foods most commonly implicated in food allergy are cows’ milk, eggs, fish, wheat, peanuts, soyabeans, crustaceans and nuts.

The foods most commonly implicated in irritable bowel syndrome are milk, eggs, wheat, nuts and fish.

Caffeine, spicy foods and alcohol can all exacerbate the symptoms of irritable bowel syndrome.

Meat intolerance is uncommon.

A food diary may show you whether there is an association between your diet and your symptoms, and suggest which foods you could try to avoid.

If a person’s symptoms are due to specific food allergy or intolerance, avoiding that particular food should resolve the symptoms within 4–7 days.

The most commonly attempted diets are the lactose-free diet and the wheat-free diet.

Beware of ‘miracle’ diets: there is no proven ‘irritable bowel syndrome diet’. Finding the right diet for you can involve a lot of hard work, diary-keeping, experimentation, discipline and luck!

Beware of avoiding so many foods that your diet becomes nutritionally inadequate. Seek professional advice from your doctor or dietitian.

As with any treatment, there is no guarantee of success, and there may be side effects.