Food Allergies

Helen Stracey

• Éditeur: Collins
• Année: 2010
• ISBN:
  9780007379644
• Sujet: Medicine
• Sous-sujet: Diseases & Allergies

This one-stop practical guide will show how to understand the allergies of yourself, your family and your friends. To make your progress easier, it comes in a handy two-colour format with expert tips and advice throughout.

1
Understanding food allergy

Food allergies or food intolerance can trigger a host of unpleasant and in some cases frightening, violent and potentially fatal responses. Symptoms can express themselves all over the body and can range from swelling of the mouth, rashes and inflammation to wheezing and digestive problems. Currently there is no cure. Avoiding the offending food is the only viable solution and the key difficulty is identifying that food correctly. The good news is, however, that in many cases, scrupulously avoiding problem foods can mean that allergies are outgrown, particularly in childhood.

Allergy or intolerance: what is the difference?

Food allergies and intolerances are on the increase, particularly in the Western world and in children, yet they still remain a rarity in the developing world. Confusion, misinformation and controversy cloud the topic. Diagnosis can be vague, opinion can vary from one GP to another and many medical professionals are wary of making incorrect diagnoses.

did you know?

In industrialized, highly developed communities, up to 20 per cent of the population experience adverse reactions to food and claim to be allergic to certain foods. However, estimates suggest that no more than five to eight per cent of children and one to two per cent of adults are affected by food allergy/intolerance and that less than one per cent of adults and one to two per cent of children are truly allergic to food.

The magnitude of the problem remains unknown, largely because the potential causes are numerous and can be difficult to identify. Many cases are mild enough to be undetected or may be misdiagnosed. Despite a dearth of statistics on the matter there is a consensus that true food allergy has increased significantly since the 1970s, particularly in the case of peanut allergy. Increased awareness and better understanding of allergies are insufficient to explain this increase. The rise in pollution levels, poor diet and certain immunizations have all been blamed for allergies in general, but the real reasons are still under investigation.

Food sensitivity

This is used as a general description to cover both allergy and intolerance. Accordingly food allergy or food intolerance are both types of food sensitivity. Some people can be ’sensitive’ to certain foods or chemicals in foods, or they can become sensitive at certain times of their life – for example, after illness, during a menstrual cycle, after a course of antibiotics, during pregnancy, in periods of stress or emotional problems and after ’overeating’ a specific food – but this does not necessarily mean they have a true food allergy or a definite pattern of intolerance.

Food aversion

This is not an allergy as such, but more of a psychological condition. It relates to a situation where a person strongly dislikes a food and believes that a food produces a particular reaction in them. Aversion usually stems from foods that are associated with sickness, nausea or gastrointestinal discomfort. So, in essence, a bad experience with food in one’s childhood can lead to aversion in later life and the belief that it causes symptoms. Sometimes the associated symptoms are similar to those resulting from intolerances, which can potentially lead to misdiagnosis. Interestingly, however, many children and seriously allergic people have a natural aversion to foods that they are genuinely allergic to – some experts believe that this is one of the body’s natural defence mechanisms.

Allergy or intolerance?

It is often very difficult to determine whether you have a food allergy or a food intolerance. The dividing line is so blurred. Many people mistakenly believe they have a food allergy when in fact they have food intolerance. One way to test this is that if you suffer from an intolerance you will usually be able to eat small amounts of problem foods without a reaction. In contrast, if you have a true food allergy, even a tiny amount of the food may trigger a serious allergic reaction. Symptoms of an allergy to any particular food also tend to appear much more quickly than the symptoms of an intolerance.

Food allergy

must know

Anaphylaxis

Pronounced anna-full-axis or sometimes called anaphylactic shock, this applies to the most severe allergic reaction, which can be potentially life threatening. Any food can cause anaphylaxis in susceptible people, if the allergy is severe. Reactions tend to become worse with subsequent exposure to problem foods.

A food allergy involves the body’s immune (defence) system and is a reaction that occurs when the body’s immune system overreacts to a normally harmless substance, known as an allergen. This can cause an immediate and sometimes a severe reaction – for example, irritation, disability and, in the extreme, death from anaphylaxis (see pages 101-102). In a true food allergy, the immune system produces antibodies and histamine in response to the specific food. The next time you eat even the smallest amount of that food the antibodies sense it and signal your immune system again to release histamine and other chemicals into your blood stream. It is this reaction by the body that causes symptoms. It is common for children to grow out of a food allergy, particularly allergies to eggs, wheat and cow’s milk. However, people with allergies to peanuts, nuts, fish and shellfish normally have the condition for life, even if they scrupulously avoid the food in question. Tests are available to test allergies that involve the immune response (see pages 77-79), but these are not clear cut. Positive tests do not necessarily imply a food allergy so a proper interpretation of results is necessary.

Food intolerance

A food intolerance describes an unpleasant reaction to an offending food. It is often triggered by foods that are both craved and eaten frequently. The jury is still out as to whether it involves the immune system, but as antibodies are not normally produced against the problem foods, it would seem that symptoms occur without the help of the immune system. The reaction and symptoms can be much more vague and slower to take effect; sometimes it can take from hours to days for symptoms to surface, making diagnosis difficult. The only reliable way to diagnose a food intolerance is to exclude completely the offending food/s to see if symptoms improve. If they do then the food should be reintroduced slowly to see if symptoms reappear. Symptoms can affect any part of the body, can be varied and are generally not life threatening. However, if you continue to eat a food to which you are intolerant, it could make you feel ill or affect your long-term health.

must know

Coeliac disease

This is a gut intolerance to gluten, a protein found in wheat and rye, and to similar proteins found in barley. The intolerance is permanent and treatment is by complete and lifelong exclusion of gluten from the diet. Coeliac disease is thought to be an abnormal immunological response rather than a lack of certain digestive enzymes. It is not considered to be a food allergy in the true sense of the definition.

Intolerances may well disappear if the food is not eaten for a few months, but they tend to recur if ever the food is eaten regularly again. Food intolerances can occur for a variety of reasons including:

Non-allergic histamine release Foods such as shellfish or strawberries can trigger the release of histamine (also released in true allergic reactions) and produce signs very similar to an allergy. Headaches, swelling, urticaria (nettle rash or hives), vomiting and diarrhoea are all common reactions. Foods with high histamine levels can produce similar signs (see pharmacological reactions below).

Metabolic defects The most common problem is lactose intolerance. A deficiency in lactase, the enzyme responsible for digesting lactose in milk causes a reduction in the body’s ability to digest lactose in all dairy products and results in an intolerance to milk. This kind of intolerance is more widespread in certain populations. For example, it affects between 50 and 90 per cent of people of Indian and Afro-Caribbean origin but only about 15 per cent of the Caucasian population. The percentage of sufferers in the UK is therefore quite low. There is some evidence, however, to suggest that lactose intolerance is increasing in the West – possibly because the high levels of dairy produce in our diet require high levels of lactase to digest them, and, as we age, most people’s lactase production declines. Furthermore, some experts believe that because inter-race marriages are much more common now, mixed-race children may carry the problematic genes.

must know

Vasoactive amines

These are normally deactivated in the body by the enzyme monoamine oxidase (MAO). People taking MAO-A inhibitor drugs (antidepressants) must avoid high intakes of foods high in vasoactive amines as they will slow the breakdown of these amines and lead to a dangerous rise in blood pressure.

Pharmacological reactions Some food substances can act like drugs particularly if taken in large quantities. The most familiar of these substances is caffeine, found in tea, coffee, chocolate and cola drinks. A large intake of caffeine can cause tremors, migraines and palpitations.

Other pharmacologically active substances found in food include the vasoactive amines (see must know box): histamine, tyramine, tryptamine and serotonin. These are powerful vasoconstrictors capable of producing in susceptible people symptoms such as urticaria (nettle rash or hives), facial flushing and headaches, nausea and giddiness. Tyramine can trigger migraine in some people. These vasoactive amines are present in many foods such as red wine, chocolate, cheese (especially if mature), fermented products such as blue cheese, sauerkraut and fermented soya products, yeast extracts, fish particularly if unfresh, pickles, microbially contaminated foods, some fruits such as avocados, citrus foods and bananas. The word ’vasoactive’ simply means that a substance causes the blood vessels to constrict or dilate – and this causes symptoms, such as flushing, palpitations, headaches and giddiness.

Monosodium glutamate (MSG) Commonly found in Chinese food and as a flavour enhancer. High amounts can cause flushing, headache and abdominal symptoms and may even mimic the symptoms of a heart attack with chest pain radiating to both arms and general weakness and palpitations.

must know

Allergic reactions

These are usually immediate, or occur at least within 72 hours of eating a particular food; they can be provoked by the tiniest amount. Food intolerance reactions tend to be much slower and are provoked by much larger quantities of food.

Food intolerance of unknown origin Reactions can be provoked by many foods and food products for which the reasons are vague. They may or may not be allergic reactions. Food additives, particularly tartrazine and sodium benzoate, can provoke urticaria, rhinitis (inflammation of mucus membrane in the nose) and asthma. Yeast products can provoke several reactions in some people, particularly skin disorders.

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Table des matières

• Cover Page
• Title Page
• Table of Contents
• Introduction
• 1 Understanding food allergy
• 2 Foods that cause allergy
• 3 Identification
• 4 Managing your allergies
• 5 Allergic children
• 6 Allergic illness
• 7 Preventing allergies
• Index
• Acknowledgments
• Copyright
• About the Publisher