Nutrition

If you think you have a food allergy, the first step is to get an accurate diagnosis.

Question:

I’m allergic to avocados, which I’ve never heard anyone else complain of. Shortly after eating even a small amount – a trace left on a knife used to cut the fruit is enough – I perspire, get severe abdominal cramps, diarrhoea and vomiting. I have a similar reaction to the painkiller Temgesic and am interested to know what the common ingredient might be.

Answer:

You’re not alone – allergic reactions to avocado are seen fairly often by specialists, says immunologist Dr Andrew Baker, although not as commonly as the main IgE-mediated food allergies.

IgE – which stands for immunoglobulin E – is an antibody produced by the immune system in response to an allergen. There are three main food-allergy types: IgE-mediated, non-IgEmediated and mixed.

“There are eight main foods that cause 90% of IgE-mediated food allergies: cows’ milk, eggs, peanuts, treenuts, soy, wheat, fish and shellfish,” says Baker, from West Auckland’s Waitemata Allergy Clinic. However, there are regional variations: sesame allergy is common in Australia, for instance, whereas reactions to mustard, celeriac and lupins are more common in Europe.

“More than 160 foods have been documented as causing a food allergy,” Baker says. Generally, proteins in food are the allergens. However, exceptions include a carbohydrate in meat called “alpha-gal”.

The most common avocado allergy is oral allergy syndrome, which usually involves localised tingling or itching in the mouth and throat and typically doesn’t progress further because the protein is destroyed by stomach acid. However, a rare, more generalised “systemic” reaction can occur if patients are particularly sensitive or eat a large amount suddenly.

Oral allergy syndrome usually occurs because of a similarity between a protein in avocado and proteins in something else. “The patient might first become allergic to latex or to a tree pollen – birch, for example – but the immune system soon reacts to

avocado, as well, because the specific protein in avocado is similar to the latex or pollen protein,” Baker says.

Someone with a latex allergy may later find they react to avocado, banana, papaya, kiwifruit or chestnut, among other triggers. “Occasionally, the issue is allergy to avocado alone, without an oral allergy syndrome, but this is less common.”

Without a full clinical history and tests, it’s impossible to determine triggers for a particular individual. However, Baker says Temgesic, a nonsteroidal anti-inflammatory drug (NSAID), can cause the same symptoms as an IgE-mediated allergy, including a rash (hives), swelling, low blood pressure and difficulty breathing (anaphylaxis). But the symptoms typically are not the result of an IgE allergy, but rather a sensitivity to how the drug works, says Baker. “If a patient reacts to one NSAID, he or she is likely to react to all NSAIDs if taken in high-enough doses.”

Up to 15% of people self-report a food allergy, but testing reveals prevalence of 2-5%.

However, the drugs can also interact with an IgE-mediated food allergy. “Some patients only react to a given food if they have taken an NSAID in the hours before. In this way, it acts as a co-factor.” Alcohol, exercise and stress are other potential co-factors.

Baker’s advice to anyone who thinks they have a food allergy is to get a diagnosis and management plan. “Sometimes people are told they’re allergic when they aren’t, and that can be very harmful in the long term, both socially and psychologically.”

Studies have found up to 15% of people self-report a food allergy. But skin-prick and specific IgE blood testing, and the double-blind placebo-controlled food challenge, which is the gold-standard allergy test, reveal prevalence of 2-5%, and occasionally higher in infants.

“This means a lot of people are labouring day-to-day under an incorrect assumption or incorrect diagnosis given to them of allergy. Proving what someone is not allergic to is just as helpful, or often more helpful, than proving what they are allergic to.”