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In the western world, 3-4 adults in 100, and 6-8 children in 100, are thought to have a food allergy. What’s more, these numbers seems to be rising each year. However, the severity of these allergies varies; in fact, many people mistakenly believe they are allergic to a certain food, but only about 1 in 5 people who report a food reaction actually have a true food allergy. One theory is that the rise in allergy cases is due to the numerous changes in children’s diet that last 30-40 years. Another theory, known as the hygiene hypothesis, is that children are increasingly growing up in “germ-free” environments and their immune system may not receive sufficient exposure to the germs it needs to develop properly. In this week’s article learn the facts about food allergies, their causes and symptoms, and how they can be managed.

What is a Food Allergy?

Food allergy is caused when the body mistakenly makes an antibody (a substance called IgE) to fight off a specific food. In other words, then that particular food is eaten (or in some cases the food is just in contact with the skin) it triggers an immune response which results in the release of histamine and other substances in the body. Consequently, these cause various symptoms depending on what part in the body they are released. For example, in the skin, rash, swelling and itching; in the gut they may cause abdominal pain, vomiting and diarrhoea; in the lower airways, a wheeze or cough, in the upper airways, a runny nose or sneezing. In some cases, the immune system chemicals are released throughout the body, causing a ‘systemic’ reaction (such as anaphylaxis).

So, what exactly happens during an allergic reaction? The protein in the food is the most common allergic component. If you are allergic to certain food, your body’s immune system mistakenly identifies a protein as harmful. Some proteins or fragments of proteins are resistant to digestion and are tagged by the Immunoglobulin E (IgE). These tags are mistaken for an invader. Consequently, the immune system sends white blood cells to attack, and that triggers an allergic reaction which may range from mild to severe.

Symptoms of food allergies

Typically, an immediate food allergic reaction will involve the immune system. Within minutes, traces of the offending food in the diet can trigger generalised rashes, itching, diarrhoea, vomiting, swelling of the lips and soft tissues, breathing difficulties and even shock. The usual symptoms include wheezing, itching, rashes, severe gut symptoms or very rarely fainting. In most cases people are aware of the food that causes the problem. Peanut anaphylaxis is a good example where traces of the food are absorbed in the mouth or intestine. This leads to the rapid release of a substance called histamine from cells and allergic tissue swelling. If you suspect you may have a food allergy, there are reliable blood tests (called IgE or RAST tests) and skin tests, available through the NHS that can show quite accurately the presence or absence of a food allergy.

So, what are the most common food allergies? The foods that most commonly cause a reaction are nuts, milk, eggs, shellfish, fish, wheat, seeds, soya and some fruits (citrus, kiwi). Even tiny amounts of the trigger food or substance can cause a reaction which means it is crucial for the individual to avoid contact with that specific food.

Food Allergy or Food Intolerance?

Food intolerance (also called non-allergic hypersensitivity) should not be mistaken for a food allergy as it is a different reaction and much more common. Contrary to what happens with a food allergy, the onset of symptoms due to food intolerance is usually slower and may be delayed by many hours after eating the offending food; the symptoms may also last longer, even until the next day.

The symptoms caused by intolerance are much more variable and can include bloating, fatigue, joint pains, rashes, migraine and various other symptoms. Food intolerance can have a number of different causes. Some people may be lacking in an enzyme that is required for proper digestion of the food. Others seem to be upset by substances that occur naturally in the food (e.g. histamine or salicylates) which don’t affect other people. There may be increased sensitivity to natural components such as caffeine, or to food additives. As a result, it is not easy to identify intolerance with a simple blood or skin test.

Lactose intolerance is one of the most common food intolerances and it causes diarrhoea and abdominal symptoms (bloating and pain) after consuming dairy products. It happens because of a deficiency of lactase, an enzyme in the body that digests lactose (the sugar) in milk. Unless lactose is broken down, the body cannot absorb it. You can be born without any lactase, or only a low level, or you can develop lactase deficiency – often after an episode of gastroenteritis.

How can you detect a food intolerance?

The most accurate way of identifying whether you have food intolerance is an Elimination and Challenge Diet. This should only take place after a consultation with a nutrition specialist as it must be planned carefully, followed strictly and for the correct period of time, in order to be effective. If your symptoms diminish or disappear with the removal of certain food items, and these symptoms reappear with the reintroduction of the food, then you have proved the cause is dietary. If there is no improvement while on the elimination diet, then food intolerance is not relevant to your condition and you should return to normal eating. As for treatment options, after the elimination diet you need to avoid the offending food(s). However, avoiding a large number of foods is not wise, as a good nutrition should include all food groups. A nutrition specialist can help you design a healthy diet plan to avoid deficiencies.

How to cope with a food allergy

There are 3 stages to manage a food allergy:

1. Identify and avoid the cause (if possible)
2. Recognize the symptoms and react accordingly
3. Be prepared for future similar situations

Preventing food allergies

Research shows that exclusive breastfeeding seems to reduce the incidence of allergies. Although in the past doctors advised breastfeeding mothers to avoid common allergenic foods such as cow’s milk, eggs and nuts, as traces may appear in breast milk, recent studies indicate it makes little or no difference to allergies. Health professionals have pointed out that avoiding all potentially allergy-provoking foods after weaning is more likely to cause malnutrition and less likely to have any long-term benefit for preventing allergies. Dietary advice for infants is a controversial subject and, despite previous recommendations to avoid cow’s milk and eggs in the first year and peanuts or nuts for up to three years, the current evidence indicates this will have no beneficial effect in preventing allergy. It is, however, important to slowly introduce new foods one at a time into a baby’s diet and keep an eye for any adverse reactions.


By Kleio Bathrellou
Associate Nutritionist & Certified Sports Nutritionist

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