Understanding Food Intolerance
The terms ‘food allergy’, ‘food intolerance’ and ‘food sensitivity/hypersensitivity’ are often used interchangeably and are often confused, but essentially they all mean an abnormal reaction to certain foods which can manifest themselves in a number of different ways.
They may result from mechanisms that involve activation of the immune system, and the subsequent production of antibodies, or reactions that are not immune-mediated.
Immune mediated reactions
Reactions that trigger an immune response are most often referred to as ‘allergies’ and occur when the body overreacts to foods that do not usually produce a response in the majority of people. This over-reaction triggers the immune system to produce antibodies to attack the ‘foreign’ food proteins which the immune system recognises as a threat.
Allergies are grouped into four types: I, II, III and IV. These classifications are based on which part of the immune system is activated and how long it takes for a reaction to occur.The two types of allergy that are most often associated with adverse reactions to food are:
Type I Allergy or IgE Response (Immediate Food Allergy)
- The best known and most studied form of food allergies is called a Type 1 immune reaction, or IgE mediated response.
- An IgE reaction occurs immediately after exposure to the allergen. With this allergy, the immune system creates an antibody called IgE (Immunoglobulin E) that attacks certain foods, causing a reaction.
- They are responsible for the ‘immediate-onset’ of symptoms that can occur within seconds or minutes following ingestion of certain foods.
- Type 1 food allergies occur in less than 5 percent of the population, and mostly in children.
- Symptoms often associated with a classical ‘allergic response’ include: rashes, sneezing, difficulty breathing and anaphylactic shock. It is usually obvious which foods are responsible for a food allergy and these have to be avoided for life.
Type III Allergy or IgG Response (Delayed Food Allergy)
- Also known as IgG-mediated allergy/food intolerance/food hypersensitivity These reactions are characterised by the production of IgG antibodies and the gradual formation of antigen/antibody complexes which are deposited in tissues, causing chronic inflammation.
- They are responsible for the ‘delayed-onset’ of symptoms, which can occur several hours or days after foods are ingested.
- Symptoms of an IgG-dependent reaction may occur hours–even days–following exposure to the allergen.
- Symptoms include: anxiety, depression, IBS, headaches/migraines, fatigue,hypertension, eczema, asthma, joint pain, chronic rhinitis, arthritis, weight problems and fibromyalgia.
- It is possible to eliminate the offending food(s) from the diet for a short period of time and then gradually re-introduce them when symptoms have improved.
Non – Immune mediated reactions
Reactions that do not produce an immune response are often referred to as ‘food intolerances’. They can be caused by sensitivities to certain chemicals/additives found in food, or more commonly due to enzyme deficiencies:
I. Lactose Intolerance
- Caused by a deficiency of lactase – an enzyme that breaks down lactose (a complex sugar)
- Foods that contain lactose include: dairy products (milk, cheese, yoghurts, etc).
- Symptoms include: bloating, diarrhoea and flatulence.
II. Histamine Intolerance
- Caused by an elevated histamine level due to a deficiency or inhibition of diamine oxidase (DAO) – an enzyme that breaks down histamine (a chemical that triggers an inflammatory response). Aggravated by foods high in histamine, including: red wine, cheese and tuna fish.
- Some foods are low in histamine, but can trigger the release of histamine in the body, including: citrus foods, bananas, tomatoes and chocolate.
- Symptoms include: migraines, dizziness, bowel/stomach problems, rhinitis, depression, irritation and reddening of the skin.