Allergies Explained - go back to home page Allergies

Grass pollen discharging granules on exposure to water - picture by Dr H Morrow Brown

Dust Mite - picture by Dr H Morrow Brown

Dr H Morrow Brown MD
General Medical Council Registered Specialist
for Allergy and Respiratory Medicine


Food Allergy and Food Intolerance

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Food Allergy

Wheat, milk, bread and eggsFood allergy is when eating a tiny amount of a specific food causes an obvious rapid reaction in any part of the body, or all over the body as in anaphylaxis,. What has happened is that an antibody called IgE has been developed towards that specific food, it is circulating in the blood, and can be detected by the RAST test. This IgE antibody sticks to the surface of special cells called ‘mast’ cells, which are to be found in the lining of the blood vessels, the bronchi, the nose, the eyes, and all over the body especially in the skin. When molecules of food are absorbed from the gut into the blood they contact the IgE antibody on the surface of these primed mast cells which triggers them to disintegrate and set free a variety of nasty chemicals, one of which is histamine.

Antihistamine tablets in foil-backed wrappingThese chemicals, usually referred to as ‘mediators’, then cause the allergic reaction to take place. Various drugs, such as antihistamines, will block these reactions to a varying extent. The intensity and speed of reaction depends on how sensitive the patient is, and how much of the food has been eaten, therefore anything from a sudden collapse to a slight swelling of the lips is possible.

A skin prick test introduces a very tiny amount of the allergen into the skin where it comes into contact with the mast cells which are already primed with specific IgE. for all the allergens to which the patient is sensitised. If the skin testing extract contains the specific allergen which reacts with specific IgE on the surface of the mast cell, that cell will explode releasing ‘mediators’ into the skin which produce itching and then secretion of fluid, producing an itchy wheal if the skin test is positive. The specific allergen can be compared to a key, which turns on the patient’s reaction only if it fits the specific IgE antibody (or lock) on the mast cells.

Food Intolerance
Problems investigated by allergists usually include anaphylaxis, acute food allergies, asthma, hay fever, perennial rhinitis, allergic conjunctivitis, urticaria and sometimes eczema. Some allergy specialists have a major interest in the immunological aspects of allergy, and are less interested in food intolerance where diagnostic tests have yet to be developed, and manipulating the diet is the only way to establish a diagnosis.

Girl who is being a fussy eaterSometimes, after reading an article in a magazine, patients with chronic problems may ask their doctors if the cause of their troubles could be in their food. This possibility is often rejected out of hand because the British medical profession are unaware that such a wide range of disease can sometimes be caused by allergy or intolerance to foods.

Until large trials of elimination diets in a variety of chronic conditions are carried out it will never be known how often food is a causative factor in many illnesses, but this is unlikely to happen because of the current tendency to suppress symptoms with medication as the first approach to treatment. Both patients and doctors want a quick fix.

Intolerance to foods presents much less well defined patterns of illness than food allergy, mainly because the association between consumption of a normal amount of the food and its adverse effects is often delayed by some hours, often the next day, or may even build up over several days. These slow reactions make it difficult to obtain clear-cut evidence if food is involved in causing the problem or not.

Skin and RAST blood tests are negative because IgE antibodies are not involved in intolerance to foods, and the actual mechanism which causes the symptoms is not completely understood. At the present time the only method which can be relied on to identify the food (or foods) causing a problem is dietary manipulation. This procedure requires some dedication and strict compliance by the patient, but when carried out properly very satisfactory results can be achieved which can revolutionise the lives of some patients.

Uncontrolled dietary manipulation can result in diets which are actually harmful, so it is very important to establish beyond doubt that the patient is truly intolerant of a specific food. To be sure it is necessary to demonstrate that the consumption of the same normal amount of the suspected food will produce the same effects after about the same time interval on two, preferably three occasions.

Looking at a blood sample in a test-tubeThere are many tests which promise to give quick answers, such as Kiniesiology, Vega testing, bio-energetics, and many others which are available in health food shops or from unqualified practitioners. Very expensive blood tests are advertised which claim to find IgG type antibodies against specific foods in a drop of your blood, but these tests which have never been subjected to acceptable clinical trials and are a waste of money.

Foods eaten daily or several times a week may not be suspected as a possible hidden cause of a chronic problem such as asthma which is controlled more or less effectively with drugs. Without trying an elimination diet for a trial period these hidden factors will never be found. Foods should be considered as a possible hidden cause of so–called "brittle" asthma, a term applied to many middle aged patients with severe asthma. This term "brittle" is simply a label which means unstable and difficult to control, and these patients are often completely dependent on oral steroids.

Changing the Organ

To make things even more complicated, the sensitised organ of the body sometimes changes over the years. For example a daily food, particularly milk, can cease to cause gut problems, and instead cause chronic eczema or asthma, as shown in the Comprehensive Diagram in the Introduction. Over a period of twenty years or more I have seen a few patients who begin with irritable bowel or mild colitis, get better with a milk free regime, then get careless about diet and develop arthritis, followed years later by asthma due to a different food. These remarkable patients often observe the connection themselves, but unfortunately have their ideas rubbished by family doctors and even by consultants in the various special departments they have been referred to, as they develop trouble in skin, joints, gut, etc. Case-histories elsewhere in this website illustrate these unusual cases. Food Intolerance is a very ill-defined condition, and there are no reliable blood tests which will tell you what not to eat to get better.

Non-Allergic Gut and Respiratory Problems

Infections, Toxins, Digestive Deficiencies, Chemical additives, Coeliac disease and Food Aversion

Everyone knows that vomiting and diarrhoea can be caused by an infection, such as salmonella, or because the food contained some toxic or poisonous substance which the body is rejecting by vomiting or diarrhoea. Sometimes people develop a psychological aversion to a food which will make them sick if they eat it For example, when an orthodox Jewish lady was told that what she had just eaten and enjoyed was pork she promptly vomited.

Sweets with strong coloured dyes in their shellChronic bowel disorders have many causes, as well as allergy or intolerance, so it is premature and unwise to jump to conclusions that a complaint is caused by an allergy, or that specific foods are causing it. For example insufficient lactase essential for digestion of milk causes diarrhoea, or gluten may cause Coeliac disease. Additives such as sulphites, flavouring agents, MSG, preservatives, and dyes sometimes cause problems, but less often than usually thought to be the case..

Abdominal symptoms can have many causes, so it is essential to consult the doctor who will, if considered necessary, arrange for an investigation by a gastroenterologist to exclude more serious possibilities before assuming that the problem is related to food.

Woman holding her abdomen, in some painSevere diarrhoea on holiday may damage the lining of the gut so that, after recovery from the acute phase, chronic problems persist. Several cases have been seen whose “irritable bowel” cleared up after avoiding milk and milk products. Reintroduction of milk a few months later caused no relapse, suggesting that the damage to the lining of the gut had produced a temporary intolerance of milk, or a temporary deficiency of the enzymes needed to break the milk down for digestion.

Abdominal symptoms can have many causes, so it is essential to consult the doctor who will, if it is considered necessary, arrange for an investigation by a gastroenterologist to exclude serious possibilities before jumping to the conclusion that the problem is related to food.

Coeliac disease is a different sort of allergy where gluten, mostly derived from wheat, causes a reaction in the wall of the gut which destroys the lining and prevents the normal absorption of nutrients, especially fats, resulting in diarrhoea, malnutrition, and many other problems. This is very important to discover because with total avoidance of gluten the wall of the gut heals and regenerates, and a complete cure is to be expected, but gluten has to be avoided permanently. In recent years blood tests for Coeliac disease have been improved and made more sensitive, and as a result milder forms of this disease have been found to be much commoner than was previously thought.

Coeliac disease is not usually classified as an allergic disease, as the antibodies are not the IgE type, and it usually falls within the specialty of gastro-enterology, but the blood tests are available to any GP through the NHS. If in doubt, ask for a test

Farmers lung, bird fanciers lung, and similar problems are caused by the inhalation of organic dusts at work or in the home environment from keeping birds, and are usually handled the Respiratory Disease Consultants. These serious lung problems are to be found in farmers, bird breeders, and pigeon fanciers, and anyone exposed to organic dusts. These problems are not related to diseases caused by inhaling inorganic asbestos or silica containing dusts which cause silicosis and mesothelioma. The cause is a reaction of the immune system to these inhaled dusts, with the development of a different type of precipitating antibody response which is not IgE.

BudgieBlood tests are available to any GP, and have been greatly improved in recent years, but the diagnosis should be made before irreversible damage to the lungs has occurred. Even one budgie is enough to cause this disease. Early diagnosis and removal of the bird will prevent unfortunate patients from becoming steroid dependent chronic invalids. I will never forget being asked to see a patient at home and found her lying on a couch right underneath the budgie’s cage! I would have been stupid not to realise the diagnostic significance of this scenario..

Coeliac disease, and lung diseases caused by an immunological reaction against an organic dust now have the great advantage that there are diagnostic blood tests available now which can lead to a diagnosis, but the possibility has to be suspected before these tests will be done. Today it is much less likely that a family doctor will know that a patient with chest problems is a prominent pigeon fancier because home visits are seldom carried out nowadays, there is little time for taking a full history, and patients do not always see the same doctor so there is no continuity of care.


"It is a paradox that while Britain has the highest incidence of allergic disease in the world, it also has the most inadequate allergy service"

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