Food Allergy

Question 1

What is an IgE-mediated food allergy?

Give examples of IgE food allergy

What are some symptoms of IgE-mediated food allergy?

Answer 1

Most common type of food allergy.

Exposure to the allergen = immune system produces IgE (antibody)

On re-exposure, the allergen binds to IgE antibodies on mast cells = triggers release of histamine and other inflammatory mediators.

This release of chemicals leads to the symptoms associated with an allergic reaction

Examples:
- nut allergy

Symptoms
rapid onset & life threatening e.g.,
- anaphylaxis
- itching
- swelling of tongue/lips
- wheezing
- vomit/diarrhoea

Question 2

What is a non IgE-mediated food allergy?

Give examples of non IgE food allergy

What are some symptoms of non IgE-mediated food allergy?

Answer 2

Allergic reactions that occur without involving IgE antibodies.

These reactions involve different components of the immune system and have a delayed onset.

examples:
- coeliac disease
- EoE

Symptoms:
more ‘chronic’ symptoms e.g.,
- Exacerbation of eczema
- Range of GI symptoms e.g., vomiting, diarrhoea, constipation, reflux
- Lethargy

Question 3

Describe food intolerance

How is food intolerance different from food allergy?

What can cause a food intolerance reaction?

What are some common food intolerances?

Answer 3

‘Food intolerance’ describe many
different conditions where consuming a certain food causes unpleasant symptoms

A food intolerance reaction is not caused by the immune system

Intolerance can be caused by:
- Pharmacological reactions (caffeine sensitivity)
- Food chemical sensitivity (benzoate: chemical preservative)
- Enzyme Deficiencies (Trehalase deficiency = mushroom intolerance)
- Functional reactions (low FODMAP)

Common intolerances:
- lactose intolerance caused by lactase deficiency
- non-coeliac gluten intolerance

Question 4

How are food allergies diagnosed?

What are the difficulties in diagnosing food allergies?

Answer 4

1. clinical assessment
2. IgE and skin prick test
3. Elimination diet

Clinical assessment:
- diet history
- symptom diary
- previous treatments tried
- establish main issue and plan

IgE and Skin prick test:
- only useful for ‘immediate’ reactions
- both can give false positive and false negative results

Elimination diet:
- single or multiple food exclusion
- few foods diet
- improvement in symptoms = reintroduction/challenge
- no improvement = change diet or abandon diet
- symptoms worse = look for other cause
people must be willing to re-introduce food when doing an exclusion diet