Food Allergy

Food, Glorious Food!

Allergies are very common and affect about one in three New Zealanders at some time in their lives. At any one time, approximately 5% of the population will have a food allergy. Allergies, including food allergies, appear to be increasing. The cause for this increase is not known.

An allergy occurs when a person’s immune system over-reacts to substances — called an allergen — in the environment. This is an IgE specific immune response. In the case of food allergies the reaction generally occurs when the allergen is ingested.

The symptoms of an allergic reaction to a food allergen range from mild to severe to life threatening. These may include:

  • Hives, eczema and facial swelling, tongue and throat swelling, cough and wheeze, nausea, vomiting, stomach pains and diarrhoea, feeling faint, becoming pale and collapse.
  • A severe life-threatening reaction (called anaphylaxis) occurs when a generalised allergic reaction affects the respiratory and/or cardiovascular systems, as well as the skin and/or gastrointestinal tract.
  • Sometimes food allergy may be less obvious, particularly in children. It can present as colic, reflux, eczema, chronic diarrhoea, or poor growth. Recent studies have found that up to 40-50 per cent of eczema cases in young children are triggered by food allergy.

Any type of food can trigger an allergic reaction; however, the majority of allergic reactions are triggered by egg, cow’s milk (dairy), peanuts, tree nuts (eg cashews, almond, Brazil nuts), soy, wheat, seeds, fish and shellfish. Egg, dairy and peanuts are the most common triggers in infants. Most children will outgrow their food allergies however allergies to peanuts, treenuts, fish and shellfish tend to persist for life. This is why peanuts, tree nuts and seafood are the most common triggers in older children, teenagers and adults.

The cornerstone in treating a food allergy is first and foremost having an accurate diagnosis, and secondly avoiding the triggers that have been identified. This will prevent any unnecessary dietary restriction and let you manage your allergy, rather than having it control you.

An accurate diagnosis is heavily dependent of a clear account of what has happened around the reactions. Keeping a food and symptom diary can be very helpful in identifying a food allergen.

Allergy tests (skin prick tests or blood (RAST or Cap RAST) tests) can be performed to help diagnose allergies – but these tests have their limitations. A positive test to a specific allergen does not mean this allergen is the cause of the allergic response; it indicates the person is sensitised to the allergen, but does not necessarily develop an allergic response. The allergy tests are only helpful if they are carried out in the context of the account of the allergic response.

Oral Allergy Syndrome

This syndrome occurs because of the immune system recognising similar allergens as being one and the same.
In New Zealand, the most common scenario is found in a person who has a birch pollen allergy, although people with grass and latex allergy may have a similar response. The reaction is generally to fruit, vegetables or nuts. The immune system sees a protein in the food as similar to the birch (or grass or latex) protein, and reacts to this. The person generally experiences a tingling or dry sensation in the mouth and throat. The reaction rarely progresses to anaphylaxis. Generally reactions are to raw foods as cooking food changes the nature of the protein.

Diagnosis can be made by skin prick testing and prick-to-prick testing i.e. pricking directly from the suspect food onto the skin.

Food intolerance

A food intolerance is an adverse reaction to a food that does not involve the immune system. Reactions can be immediate or delayed up to 20 hours after a food is eaten.

Symptoms of intolerance are sometimes vague and can include a combination of the following: gastrointestinal problems such as bloating and wind, diarrhoea, nausea and indigestion, aggravation of eczema or asthma. Food intolerances can sometimes mimic symptoms of other medical conditions – it is important to get checked out by a doctor to eliminate other problems first.

The cornerstone of a diagnosis of food intolerance is again an accurate account of symptoms and possible associations with food. Keeping a food and symptoms diary is very helpful.

There are no tests to diagnose a food intolerance. The diagnosis is very much dependent on removing a suspect food from the diet, recording whether symptom improve or disappear, and then reintroducing the food to see if the symptoms return. This removal and reintroduction of food is best done under the guidance of a dietician, who will be able to make sure you completely removed the suspect food group, while still maintaining a healthy balanced diet.

Lactose intolerance

Lactose intolerance is not a milk allergy, as it is not an immune response to the cow’s milk protein. In the majority of cases, lactose intolerance are caused by a lack of the lactase enzyme that breaks down the sugar, lactose, found in milk. People can develop lactose intolerance at any time as lactase levels drop soon after birth; however, it is unusual in children under 5 years of age.

Salicylate intolerance

Salicylate is a naturally occurring chemical found in some plants and also in Aspirin. People with salicylate sensitivity have varying levels of salicylate they can tolerate. Some people will be able to eat a small amount of the fruits and vegetables containing salicylate whereas others will need to avoid these foods completely.

The symptoms of salicylate intolerance vary but include rashes, eczema, asthma, urticaria and angioedema (swelling), stomach aches and crampls.

There are no tests that can diagnose a salicylate intolerance; however, a skin prick test may be necessary to exclude a true IgE allergy.