What is a food allergy? How is a food allergy diagnosed?

Author: Ingrid Roche, Accredited Practising Dietitian | FOOD ALLERGY

What is food allergy?

In Australia, 90% of food allergies are caused by 9 foods. These are egg, cow’s milk, soy, peanut, treenuts, wheat, fish, shellfish and sesame. It’s important to know, though, that ANY food can cause a reaction, and there are over 170 foods that have been documented to cause food allergies. Yep, even watermelon and potato!

A food allergy ALWAYS involves the immune system. Food intolerances don’t.

There are two types of food allergies – “IgE mediated” food allergies, and “non IgE mediated” food allergies.

Let’s start with IgE mediated food allergy. Sometimes the immune system makes immunoglobulin E (IgE) antibodies to food proteins (same as what it does for other proteins, like nasty bacteria that it needs to defend us against). When that food allergen enters the body, the immune system produces lots of IgE antibodies which bind to mast cells – these mast cells then release histamine and other inflammatory chemicals which are the cause of the allergic symptoms.

IgE mediated food allergy symptoms can occur within minutes of eating the food. Occasionally they will occur a little later but usually within 2 hours. Mild to moderate symptoms include:

  • Swelling of lips, face or eyes
  • Hives
  • Tingling mouth
  • Abdominal pain
  • Vomiting
  • Eczema or rashes

Anaphylaxis is the most severe allergic reaction – it’s life threatening and includes any one of the following symptoms that need immediate treatment with adrenalin (EpiPen):

  • Difficult or noisy breathing
  • Tongue swelling
  • Swelling/ tightness in throat
  • Difficulty talking / hoarse voice or cry
  • Persistent cough
  • Dizziness or collapse

These symptoms are very scary. Often people go straight into anaphylaxis with no mild symptoms to start off with.

Non IgE mediated food allergy still involves the immune system, but not IgE antibodies. Other immune processes are involved in releasing the inflammatory chemicals. Symptoms can occur quickly after eating, but may be delayed, 2-4 hours after eating, and sometimes the symptoms are chronic. Symptoms usually involve the gastrointestinal system and include vomiting, diarrhoea and pain. There are a number of non IgE mediated allergic syndromes, including food protein induced enterocolitis syndrome (FPIES); eosinophilic oesophagitis; enteropathy; proctocolitis; reflux; constipation; and multiple food protein intolerance – usually seen in infancy. Eczema can also be non IgE mediated. We will be writing more about these types of allergies in future articles.

How is food allergy diagnosed?

Ok, it’s super important to get food allergies diagnosed correctly. This is a tricky business so make it a priority to see someone with the appropriate training. This means you need to see a paediatric immunologist or adult immunologist; or a paediatrician or adult physician with specialist training in allergy. Some general practitioners have a special interest in allergies and may have had appropriate training under the supervision of an immunologist (hospitals have training programs for GPs and physicians wanting to specialise in allergy).

There are 3 scientifically validated methods for allergy testing. All of them MUST be used in conjunction with the person’s clinical history (what happened, when, what food was consume). These methods are not a stand-alone diagnosis without the clinical history.

  1. Skin prick testing – this is where a droplet of allergen extract or fresh food is placed on the skin and a lancet is pricked through it – if the person has IgE antibodies to the allergen, a red wheal or welt will appear on the skin over 15 minutes or so. The size of the wheal is measured and recorded.
  2. Serum specific IgE – this is a blood test that measures whether the person has IgE antibodies to specific foods.
  3. Oral food challenge – this is considered the ‘gold standard’ of diagnosis – give the food to the person and observe what happens. This is more useful for mild or moderate reactions. A high level of medical support is needed to do this if someone has had an anaphylactic reaction to a food.

There are a couple of limitations with skin prick tests and the blood tests. Sometimes the immune system will produce IgE antibodies to a food, and this will show on the tests, but the person is able to eat the food without any problems at all. In this situation the immune system has behaved ‘normally’ and has mounted a ‘tolerance’ response. When an allergic reaction happens, it’s an ‘abnormal’ immune response to that food allergen. This is why it’s important to only test foods that you suspect may be the problem, and in the case of infants, only test foods they have actually eaten. Keep in mind that infants might have positive tests to particular foods, but if they’ve never eaten the food you don’t know if they are actually allergic to it! This is also why it’s important to see someone trained in allergy to interpret the results of IgE tests.

The other limitation is that non IgE mediated allergies don’t show up on skin prick tests or blood tests, so diagnosis happens by the clinical history, and food challenges.

Some health practitioners use other methods to diagnose food allergies and intolerances, but none of them have been able to be validated by scientific methods. They include Include IgG testing (which is particularly misleading), cytotoxic food testing, kinesiology, Vega testing, electrodermal testing, pulse testing, reflexology and hair analysis. No allergy society worldwide recommends these methods for diagnosing food allergy.

Accurate diagnosis and good management of food allergy is so important

Food allergy has been shown to have a greater negative impact on quality of life than childhood diabetes. Individuals and families with food allergies can be severely affected by anxiety. Trusting other people to look after your child when you know the smallest exposure to a food can trigger a severe reaction, is extremely difficult. As a parent it is understandable that you would want to know exactly what the level of risk is and how strictly you need to avoid the allergen. Doctors, nurses and dietitians who specialise in food allergy can help you navigate the world of allergy tests, treatment, and creating a safe and nutritious diet.

Sometimes allergies can be very specific – you may be allergic to one treenut but tolerate others; or just be allergic to a specific type of fish; or tolerate cow’s milk or egg in baked form but not fresh. An accurate diagnosis by an allergist and management by an allergy dietitian can help expand the diet rather than it being more restricted.  Follow up is also important, because children in particular usually grow out of milk, egg, wheat and soy allergy so you want to be seeing your allergist regularly to see whether the allergy is resolving and whether it’s time for food challenges.

Excluding foods and whole food groups from your diet is difficult and can be nutritionally risky and annoying socially! So, you only want to avoid foods if it’s absolutely necessary. Misdiagnosis or guessing can result in unnecessary avoidance of foods, and end in nutritional deficiencies. There are documented cases of nutritional rickets in children, growth failure, malnutrition, vitamin and mineral deficiencies in children and adults with food allergies, sometimes due to unnecessary restriction of foods. For example, unnecessarily cutting out dairy can result in lower bone density, cutting out wheat can result in inadequate intake of iron and B vitamins. If you or your child is allergic to multiple foods, it’s definitely worth seeing us for a thorough nutrition assessment and advice to optimise the diet.

In the world of adverse food reactions, allergy testing with a scientifically valid method is the best place to start. If that all turns out to be negative, you can then move onto looking at food intolerances, which is a story for another blog.

About the Author

Ingrid Roche is a Perth Dietitian specialising in food allergies, paediatric nutrition and pregnancy nutrition. She is the co-founder of Advanced Dietitians Group and loves working with people and families. She has been a dietitian for 23 years. She continues to work as a Senior Paediatric Dietitian and as the allergy dietitian at Perth Children’s Hospital and has worked in various hospitals in Western Australia and the Northern Territory. When she is not working, she is trying to keep up with her three young adult kids!

About Advanced Dietitians Group

Advanced Dietitians Group was founded in 2014 by Belinda Martin and Ingrid Roche, Perth dietitians with a combination of over 40 years’ experience in the industry. Both dietitians have a range of experience across the lifespan but specialise in paediatric nutrition, pregnancy nutrition, infant nutrition and food allergies. They provide up to date evidence-based nutrition advice. This coupled with their wealth of experience in dietetics ensures you get the best possible nutrition service. They get a buzz out of helping their clients and their families.

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