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The foods that leave a bad taste

IT IS common to hear about someone having a food intolerance or allergy; if you don't have one yourself, chances are you will know someone who does. In fact, according to the Irish Nutrition and Dietetic Institute (INDI), Irish statistics indicate that approximately 5pc of children and around 3pc of adults suffer from food allergies.

This is reflected on product labels, which frequently display warnings of nut traces, etc, while restaurant menus are increasingly catering for allergies and intolerances. But what exactly is a food allergy? Is it the same as a food intolerance? And how can you tell if you have one, or one of your children has?

Actress Jessica Simpson reportedly has numerous food allergies, and it's been claimed she cannot eat cheese, wheat, tomatoes, hot peppers, corn or chocolate.

Although food allergies and intolerances are often referred to together, they are actually different. Food allergy symptoms occur when the immune system incorrectly recognises a particular food as harmful. A food intolerance, on the other hand, is an adverse reaction to a food which occurs when the body is unable to digest that food successfully. Read on for the full lowdown on all things food allergy and intolerance-related.

>Food Allergies

So what actually happens with a food allergy?

The allergy causes your body to produce antibodies and a complex chain of events occur, leading to the release of substances such as histamine.

The histamine release causes the symptoms of allergy, including asthma, rhinitis, conjunctivitis and, in its most severe form, anaphylaxis, which is potentially life-threatening. An allergic response to food always involves the immune system and symptoms are frequently seen within minutes, although some allergic reactions can have delayed symptoms.

Although some people take it upon themselves to "diagnose" a food allergy, it is very important to visit your GP if you suspect you may be allergic to a particular food. Cutting out certain foods without the proper diagnosis or supervision from a doctor can cause further health complications. Your GP may also refer you to a dietitian, who will advise you on the proper avoidance diet to adhere to, including alternative sources of nutrients.

Food allergies can be diagnosed in different ways. Skin-prick tests are used to determine the reaction to a range of foods. They can also indicate if the problem could have been caused by other common allergens (such as dust, cat hair or pollen), as well as provide an indication of how strong the reaction is. Blood tests are used to determine the strength of the immune system response to an allergen. This usually involves a radioallergosorbent (RAST) test, where the level of IgE antibodies (the kind associated with a food allergic reaction) are measured.

According to the INDI, allergen provocation tests are generally regarded as being diagnostically the most definitive. The double-blind placebo controlled food challenge (DBPCFC) is used to administer the suspected allergenic food to the patient orally under clinical supervision. The DBPCFC can be risky for people who may have a severe food allergy and in this case is only carried out in a hospital setting with full resuscitation equipment.

The most common food allergens are: cow milk, eggs, shellfish, fish, soya, peanuts, wheat and tree nuts. These foods are responsible for up to 90pc of all allergic reactions. However, allergic reaction to newer allergens such as sesame and kiwi fruit are becoming increasingly common.

>Food Intolerance

Food intolerances don't involve the immune system, are rarely life-threatening and generally occur hours, or even days, after the food has been ingested.

The symptoms are generally described as an unpleasant reaction to a particular food, with the most common examples of food intolerance being coeliac disease and lactose intolerance.

Coeliac disease occurs because the body can't tolerate gluten (a protein found in wheat, barley and rye). Lactose intolerance occurs when the body does not have the enzyme to digest lactose -- although this is very different to cow milk protein allergy.

A food intolerance is diagnosed by your GP, who will do a physical check-up to rule out other medical problems. Your dietary history will be investigated.

This will include a description of your symptoms and the foods you suspect of triggering these symptoms. Your family history is important, so investigate whether there is a history of intolerances before visiting your doctor.

This is known to be a significant risk factor, and having the information in advance can help speed up a potential diagnosis.