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Food Allergy & Intolerance


Food Allergy & Intolerance


Michael Sellar

An allergy is any reaction to a food or something in the environment that gives rise to an immune response. Originally, there had to be a positive skin prick test before a diagnosis of allergy could be given.

For a food to be described as an allergen (an allergy causing substance), there had to be a fairly immediate and violent reaction to it, involving swelling of the lips and mouth, vomiting, and in the most serious cases, anaphylactic shock. This is now described as classical food allergy.

In the 1960’s, immunoglobulin E (IgE) was discovered. This antibody was shown to be the main culprit in allergy. A way of measuring the level of these antibodies to a specific allergen was soon developed called a radioallergosorbent test (RAST). Some doctors only accept a positive skin prick test or RAST as proof of allergy.

The problem with this is that not everybody fits into this neat category. It is possible for there to be an immune reaction that doesn’t involve IgE. The results of these tests would be negative in such cases. It is possible for there to be no immune system involvement at all, although chemical messengers are released in the same way as if there was an overproduction of IgE.

It is possible to have reactions to food that are quite different from classical allergy yet give rise to a wide range of symptoms. These are usually called food intolerances.

There are 5 classes (isotypes) of antibodies. IgA, IgD, IgE, IgG and IgM. Unlike the other isotypes, IgE molecules attach themselves to mast cells, (connective-tissue cells similar to basophils except that they do not circulate in the blood). The main purpose of IgE is to protect the body against invasion by parasites, and so most mast cells, although found all over the body, are more common around the nasal passages, bronchi, and intestines. Up to 100,000 IgE molecules can reside on the surface of each cell.

When the allergen enters the bloodstream, it attaches itself to the antibody. It has to cross link two or more antibodies to trigger the mast cell to explode, discharging histamines and other chemicals. Each of these chemicals has an effect on other tissues, producing inflammation and smooth muscle contraction.

Although the body should only be making IgE in response to parasitic invasion, for some reason the mechanism goes wrong and innocuous substances come under attack. And just to complicate things, although allergy prone people would be expected to have a higher IgE level in the blood, not all do. And some people who have higher levels in the blood are symptom free.

To act as an antigen, i.e. to give rise to antibodies, the molecule has to be above a certain size. Most antigens are proteins. Smaller molecules are thought to be able to combine with proteins. Certain foods are more allergenic than others, though it isn’t clear why.

Although food allergens would be expected to cause symptoms in the mouth, they can be responsible for asthma or eczema. Similarly, inhalant allergens can cause skin problems.

Where allergies are inherited the term atopic is used. Faulty genetic information is known to be responsible in these cases, although other factors are also at work.

Although most allergies begin at an early age, the initial exposure to the allergen cannot cause symptoms because no antibodies have yet been formed.

A reaction might occur on initial exposure to a food if molecules have passed from mother to baby before birth or during breastfeeding. The symptoms of allergy often disappear as the child grows although some believe that symptoms are merely suppressed and recur possibly in a different form in adulthood. Food allergies can be responsible for any of the classic allergy diseases: asthma, eczema, hay fever, urticaria, and rhinitis.

Immune Complexes

Not all food allergies are caused by IgE. It is not unusual for food molecules to enter the bloodstream after a meal. Peyers Patches - part of the immune system that lies in the wall of the intestines - samples the gut contents and communicates how the rest of the immune system should respond. Since food is not a threat to the body, non-inflammatory IgA antibodies are formed and link up with any food molecule antigens that are absorbed.

These immune complexes are normally cleared by phagocytes in a few hours. It is believed, although not proven, that in allergic people the gut wall may be more leaky than usual, creating a large number of immune complexes that are difficult to clear and end up deposited in blood vessels, causing pain in the joints, skin rashes, and kidney damage.

False Food Allergy

Some food molecules are able to fool the mast cells into exploding and thereby releasing histamine and other chemicals even though no IgE antibodies have been formed to the food.

Several groups of compounds found in food are known to have this effect. These are lectins, found in peanuts, beans, peas and lentils; peptides, found in fish, prawns, shrimps, crabs, lobsters, pork, egg-white, tomatoes, strawberries, alcohol and chocolate.

Other chemicals that can do the same are found in buckwheat, sunflower seeds, mango, mustard, fresh pineapple and papaya. A modified RAST is able to distinguish between true and false food allergies. Magnesium deficiency affects around half the sufferers of false food allergy. This mineral is known to affect sensitivity to and release of histamine.


A leaky gut will allow more histamine, which is formed in foods by the action of certain bacteria, to get into the bloodstream. This can give rise to headaches, rashes, sickness and diarrhoea. The chief culprits are fresh mackerel and tuna, tinned fish, well ripened cheeses, sauerkraut, continental sausages, many alcoholic drinks. People with chronic urticaria are particularly susceptible to histamine in foods.

Food Intolerance

Intolerance differs from allergy in a number of ways. With allergy the immune system is considered to be involved. With intolerance the immune system has not been shown to be involved, although that doesn’t preclude the possibility.

Allergic reactions are fairly immediate. With intolerance the reaction can be many hours or even days later.

People can be allergic to foods that are rarely eaten. The intolerant patient reacts to foods that are eaten regularly. Even the tiniest smear of an offending food can provoke an allergic reaction. Larger amounts are needed to provoke intolerance.

Allergic people may remain that way for life. Intolerant people may become tolerant to the food eventually if it is avoided for a long time.

Allergic people do not crave the offending foods. The intolerant person often does. The allergic person has a limited range of symptoms. With intolerance, the symptoms can be many and varied, can come and go, and vary in intensity.

Allergies are confirmed by skin prick and RAST. Intolerances are confirmed by an elimination diet, although a number of other tests have been devised.

Why Does It Occur?

This is unknown, but some believe it is a failure of the body to adapt to the change in diet over the last 10,000 years. From eating a variety of wild plants and animals, man started to farm, cultivating wheat, keeping hens and cattle for beef and dairy foods. In evolutionary terms this is a very small amount of time. Others believe that it is more a problem of improper weaning.

How common the problem of food allergy and intolerance is, varies greatly from conservative orthodox doctors who consider the problem to be quite rare, to others who suggest that virtually everybody is intolerant to one or more foods even if they are not aware of it.

Those that believe the problem to be quite common suggest that the symptoms of food allergy and intolerance are extremely wide ranging. Over 100 symptoms have been put into physiological categories by Dr. Mandell, author of Dr. Mandell’s 5-Day Allergy Relief System. The most common symptoms are gastrointestinal in nature: diarrhoea, constipation, wind etc. Others include headaches, fatigue, depression, anxiety, hyperactivity in children, recurrent mouth ulcers, muscle aches, ulcers, nausea, joint pains, and water retention.

Irritable Bowel Syndrome

This is one of the most common gastrointestinal problems. Symptoms include: absence of a regular pattern of bowel movements; frequent diarrhoea, constipation, or alternating bouts of each; bloating or swollen abdomen; abdominal pain or cramps; excessive gas. Related symptoms may include fatigue, depression and anxiety.

A number of studies have implicated foods. One study showed that improvement was most likely where diarrhoea was the most dominant symptom. 9 out of 17 patients improved significantly on a two week elimination diet of lamb, fresh white fish, cabbage, carrots, peas, ‘Ryvita’, milk-free margarine and black tea.

14 out of 21 patients eating only lamb, pears and distilled or spring water for one week reacted to specific foods introduced one at a time. Wheat was the most common culprit.

A large study of 188 patients found that 65% of them benefited on an elimination diet, and could identify the offending foods when they were reintroduced. The commonest offender was wheat.

Crohn’s Disease

Dr. Hunter of Addenbrooke’s Hospital, Cambridge reports that 80% of his patients recovered on an elimination diet. They reacted to specific foods when reintroduced. Of those, 80% have stayed well by keeping away from the foods they reacted to. Another trial has confirmed the good effects of eliminating the intolerant foods with a long term recovery rate of 50%.


During a migraine attack, the blood platelets clump together, releasing a large amount of serotonin causing the blood vessels in the brain and throughout the body to constrict. The body counteracts the effects of this, but this causes the blood vessels to dilate more than normal.

Until recently, the most popular theory to explain what caused the platelets to clump together in the first place was that tyramine and phenylethylamine found in the brain and in certain foods are not broken down properly by the platelets in migraine sufferers. The foods rich in these amines being chocolate, red wine and cheese. However only a small percentage of sufferers are affected by these foods.

When a broad dietary approach is used a success rate of 80-90% has been achieved. Many studies convincingly demonstrate the benefits of eliminating intolerant foods. In a 1979 study of 52 migraine patients, 85% became headache free after eliminating wheat, oranges, eggs, tea, coffee, chocolate, milk, beef, corn, cane sugar and bakers yeast.

A study published in The Lancet in 1983 involved 88 children with severe and frequent migraine. 78 of them recovered completely on an elimination diet and another 4 ‘improved greatly’. Only 6 children did not respond. 8 continued to remain well even when foods were reintroduced into their diet. 74 children were shown to be affected by particular foods. 40 children were retested double blind, 35 of whom reacted to a tin of food containing the suspect food but not by the placebo. A most impressive result. This particular group of children also suffered from many other problems such as epileptic fits, hyperactivity, abdominal pain, diarrhoea, mouth ulcers etc. In the majority of children these problems cleared up as well.

Rheumatoid Arthritis

It is thought that around a third of patients can stay symptom free by avoiding the foods they are sensitive to. In one study 33 out of 45 patients considered their condition to be ‘better’ or ‘much better’ following dietary therapy.

Multiple Sclerosis

Chocolate has been implicated in some sufferers. Cutting it out of the diet has stopped any further decline. The other main incriminating products are milk, tannin, caffeine, and yeast.

Mental Symptoms

There are many well documented cases of serious mental disorders, the root of which has been found to be food sensitivities. Symptoms reported apart from anxiety and depression include poor concentration, poor memory, confusion, mental exhaustion and fatigue, irritability, violent mood swings and aggression.

As early as 1954, Dr. Speer described ‘allergic tension fatigue syndrome’ in children. The most commonly implicated foods being milk, wheat, egg, beef, corn, cane sugar and chocolate. In adults the term ‘cerebral allergy’ has been used.


Some practitioners believe that excess weight has more to do with water retention than fat. Food intolerance is said to cause the peripheral arterial capillaries to leak fluid. There is no doubt that many people are able to lose weight once the foods that they react to are eliminated.

Testing For Food Intolerances

Some practitioners start off their patients with just turkey and pears or turkey, pears and rice. Others allow the patient to eat a dozen or so foods not often eaten. An alternative is to eat a diet of rare foods; exotic and unusual foods that the patient may never have eaten before. Another alternative is a rotation diet. Allowed foods are separated into groups of four. The foods in each group are the only ones eaten each day, so there is a four day separation between each type of food. Another alternative is to leave out the most common foods that people react to only.

There is always the problem of compliance when dealing with suspected food intolerances in this way. An alternative is to use blood tests.

There are two blood tests available that have a reasonable degree of accuracy. The first is the cytotoxic test which observes whether white blood cells react with each food extract. This is considered to be up to 80% accurate under best conditions.

The problem in the past has been that it needed to be carried out under strict conditions with an expert operator and was rather subjective. Now however these drawbacks have been eliminated with the new automated version that is now available using a haematology analyser.

The second is called the Enzyme Linked Immunosorbant Assay. This measures the IgG antibody reactions to each food. It is claimed to be 95% reproducible.

There are also other tests used by complementary health practitioners such as NAET. For details of this test and others please go to
Food Allergy & Intolerance

This article was first published in Enzyme Digest No.s 28 and 29 1996

Any health and medical information published on this website is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.