Food Allergy! What Is It and Why Do We Have It?

Food Allergy! What Is It and Why Do We Have It?

Why do we have allergy?

Allergy is actually a reaction of an overreactive immune system that produces IgE (antibodies) against harmless specific food proteins.

Think of our immune system like a troop of soldiers, ready to attack invaders. Allergy reaction is when the troop saw a harmless civilian and attacked it like an enemy. There are soldiers in this troop that remembers the face of the invaders and if they come again, they will attack them (causing allergy reactions).

Allergy reaction usually happen after 10mins to an hour after ingesting the allergen.

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What are some common allergy reactions?

There are different severity in allergy reactions. The milder versions are:

  • Eczema
  • Hives/rashes
  • Red and itchy patches
  • Nauseous and stomach pain
  • Tingling of mouth or tongue

Severe reactions are:

  • Breathing problems
  • Swelling of tongue or throat
  • Difficulty to talk
  • Dizziness or fainted
  • Pale and weak

These severe reactions can cause death if symptoms are not controlled in time. If people started to have severe reactions, need to call emergency at once because reaction sometimes become milder slightly but magnify a while later. If they have carried an Epic-Pen with them, must help them inject ASAP. For the milder reactions, also need medical attention and try to drink lots of water to flush out the allergen.

Who are at risk?

Allergies can happen to anyone, anytime. Although it is true that it is usually more common in children and they do tend to outgrow their allergies. In Hong Kong, about 5% of children has food allergy and if the child has eczema before the age of 6 months, their chance of experiencing food allergy would be higher. However, first time occurrence can happen at any age and allergy reaction can come back to revisit later on in life.

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What are the foods that are likely to cause food allergies?

  • Eggs
  • Peanuts and other nuts
  • Cow’s milk
  • Seafood
  • Wheat
  • Soy
  • Some fruits (apples, peaches, plums, cherries, bananas, citrus fruit)


What sort of tests can we do?

  • skin prick test (usually for children)
  • Blood test (more thorough)


What can we do nutritionally?

First you will need to confirm what is/ are your allergens. If in doubt, you will need to at least have some suspicious triggers. Usually if there is a suspect or confirmed food allergen(s), we can try exclusion diets. There are different levels of exclusion diets:

  1. Single exclusion diet – exclude the single food source that triggered the allergy
  2. Multiple food exclusion diet – as the name suggests, this diet is to exclude a number of foods at the same time. It is usually used when dietary link is not identified.
  3. Few food diet – only use a few foods for the diet. This method is only used if multiple exclusion diet failed. This needs to be discontinues after 2-3 weeks to avoid malnutrition. 

When patients are on any of these trial diets, they must record their food diary clearly, preferably a week before starting the food trials, during the food trials and when reintroduce the suspected food (unless the allergen create severe allergy reactions).

These food trials are best to be done with a friendly dietitian, because when we exclude any foods, you may risk certain nutrients missing which need to be replaced by similar foods that provide the same nutrient without the allergy reaction.



Food allergies can happen any time even if those foods used to not trigger allergy, it may become a problem later in life. If in doubt, best to consult your GP and seek nutrition advice with a dietitian.

about the Author:

Healthy Eating, Nutritionist, Healthy Diet
Liza Chan, APD (DAA, Australia)

Liza Chan

Accredited Practicing Dietitian (DAA, Australia, APD registration number APD002107)
Master of Nutrition and Dietetics (University of Sydney)
Diploma in Sports Nutrition (International Olympic Committee)

Be Smart, Eat Smart with Liza
Visit me on Instagram: friendlydietitian2019

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