IMMUNE-MEDIATED REACTIONS
Reactions that trigger an immune response are most often referred to as ‘allergies’ and occur when the body over-reacts 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
Also known as IgE-mediated allergy/Type I hypersensitivities/true allergy

These reactions are characterised by the production of IgE antibodies and the release of histamine, and other chemical mediators, upon exposure to an allergen (e.g. peanuts and shellfish). They are responsible for the ‘immediate-onset’ of symptoms that can occur within seconds or minutes following ingestion of certain foods. 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
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 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.