Food Allergy And Intolerance

chronic fatigue syndrome The terms food allergy and food intolerance both describe food sensitivities: adverse reactions to food, that the majority of people could safely eat. There is a lot of confusion when it comes to correctly describing reactions that are attributed to food. When food sensitivities involve the immune system they are termed food allergy, whereas when the immune system is not involved the term food intolerance is used.

What is food allergy?

This description includes adverse reactions to foods, which are caused by an immune system response. Around 5% of children and 4% of teenagers and adults have food allergies2. Incidence of food allergy is increasing.

Classical food allergy response

In the case of classical food allergy, the body has incorrectly made a specific immunoglobulin E (IgE) type of antibody of a certain food. Antibodies are present on immune cells in the mucosa (tissue lining body cavities and openings, e.g. nose, mouth, eyes, gut and organs), skin and in the blood. When the IgE antibodies come into contact with the proteins from the allergenic food, this triggers the release of chemical messengers including histamine, which are messages telling the immune system to mount a defence response. The problem is that the food protein is not a dangerous disease-causing virus or bacteria, but the body still mounts a serious attack as if it were. The most common foods to cause IgE type reactions in young children are: 2
  • Milk
  • Egg
  • Peanut
  • Tree nuts
  • Fish
  • Crustacean shellfish
  • Wheat
  • Soy

Other food allergies

Other types of food allergies are those still thought to involve the immune system, but not predominantly to do with IgE antibodies. These are often referred to as non-IgE-mediated food allergies, some examples are:
  • Eosinophilic gastrointestinal disorders (e.g. eosinophilic oesophagitis, eosinophilic gastritis and gastroenteritis): this type of reaction involves large numbers of a type of immune cells (eosinophils) congregating to areas of the digestive system which causes prolonged tissue inflammation.
  • Constipation due to non-IgE food allergy: a recognised symptom of food allergies, commonly a reaction to cow’s milk which can affect children who had previous symptoms of an IgE classic milk allergy when they were younger.

Other diseases related to food allergy

Coeliac disease is an autoimmune disease not generally grouped with food allergies, although certainly involves an immune reaction to food. The body triggers an immune system reaction in response to ingestion of gluten, resulting in damaged tissue in the small intestine. For more information see NHS Choices. . Immune reactions to specific foods have also been shown to play a role in Crohn’s disease.1

What are the symptoms of food allergies?

Symptoms of IgE-mediated food allergies typically occur in minutes or up to 2 hours after allergic exposure. Other food allergy reactions can occur hours or days later. Symptoms include tingling, itching, nettle-sting-like-rash, swelling (e.g. face, lips, tongue and around the eyes), sneezing, congestion, cough, shortness of breath, wheezing, nausea, stomach pain, diarrhoea and vomiting. Conditions concurrent with IgE food allergies include asthma, atopic eczema and allergic rhinitis.

Symptoms vary depending on how severe the food allergy is. Anaphylaxis describes a strong allergic reaction throughout the body, a serious, potentially life threatening condition. You can find out more about anaphylaxis at NHS Choices

What is food intolerance?

It is not surprising the terms food allergy and intolerance cause much confusion. The same food components can be a trigger of food allergies in some people or be attributable to a food intolerance in others. In the case of cow’s milk, this could cause an IgE mediated allergy (cow’s milk allergy), or a non-IgE mediated allergy (e.g. Eosinophilic disease), or food intolerance due to a metabolic mechanism (lactose intolerance), or idiopathic food intolerances (of no known cause). The main difference to remember is that food intolerances are sensitivities to food that have no currently recognised immune system involvement, although some food intolerances can resemble the symptoms of food allergy. Some examples of types of food intolerances include:

Idiopathic (unknown reasons): Food sensitivity reactions with no identified mechanism of how they are caused. For example scientists are unsure as to how many artificial colours and preservatives trigger sensitivity reactions. Metabolic (involving enzyme deficiency and poor absorption): A common example is lactose, which can trigger adverse food reactions in people that have an enzyme deficiency. The enzyme lactase is used to digest the sugar lactose in milk. When lactose is not broken down it causes symptoms of bloating, pain and loose stool. This is known as lactose intolerance. Biogenic amines e.g. histamine: Biogenic amines in food can cause toxic effects when present in high amounts, which can occur when food becomes contaminated with bacteria. However some people are more sensitive to biogenic amines, which are naturally present at higher levels in certain food (fermented food, strong cheese, red wine, tuna and mackerel fish and cured sausages). Histamine is the same chemical released in IgE reactions, therefore symptoms can be like those of classic allergy.

What are the symptoms of food intolerance?

A wide variety of body-wide symptoms, seemingly unconnected are associated with food intolerance. Food sensitivities that may trigger symptoms in certain conditions (e.g. rheumatoid arthritis, migraine, IBS) are classed as food intolerances, until a point that research can confirm clearer mechanisms. The symptoms of food intolerance can also mimic those of food allergy.

Diagnosing food allergy and intolerance

It is important to identify food allergies and intolerances so that appropriate treatment and information can be given. Some people who suspect allergies or intolerances may find out their symptoms are caused by a different condition. It is generally regarded that sensitivity reactions relating to food allergies are reproducible upon exposure to suspected food and/or are improved by avoidance of specific foods. This can be less straightforward in the case of multiple food sensitivities, and reactions to food, which develop some time after exposure. This is often the case with food intolerance. Assessment and appropriate testing therefore requires expert interpretation and should only be carried out with medical supervision in medical facilities (e.g. equipped to deal with anaphylactic reactions). Depending on individual presentation, diagnosis may include:
  • Full allergy-focused medical history and examination
  • General blood tests
  • Blood IgE antibodies
  • Tests for eosinophils
  • Skin prick test
  • Atopic patch test
  • Oral food challenge test
  • Food elimination diet
  • Referral for other clinical examinations or diagnostic tests, e.g. endoscopy and tissue biopsy.
  • Stool test
  • Appropriate referral to specialists

Elimination diets

An elimination diet is used as a diagnostic tool for food allergy and intolerance. Different foods are excluded from the diet with the hope that the right foods have been chosen and symptoms improve. As implied, it isn’t always the case that the right foods will be chosen first off and different elimination diet trials may be necessary. If symptoms do improve then the idea is to find out which foods trigger symptoms, by systematically and singularly introducing foods back into the diet. It is advised that elimination diets are followed under medical and/or nutritional supervision to make sure they:
  • Are carried out purposefully and methodically
  • Are clinically indicated and safe
  • Are adapted for children of different ages
  • Are short term
  • Do not unnecessarily exclude food groups for long periods without re-testing,
  • Are followed through to the stage of re-introducing a diet which supports symptoms

What can you do to support your health when you have food allergies or intolerances?

Food allergies and intolerances can seriously affect health and quality of life. If food triggers are identified, it is important to follow treatment advice and practices such as strict avoidance of those foods. Diet and lifestyle strategies include:
  • If you suffer from serious allergies, reading food labels is especially important
  • Research food products that contain trigger foods and common label synonyms
  • Cook from scratch to avoid multiple ingredients and hidden contaminants in ready-made food
  • Limit convenience foods (e.g. snack bars and biscuits) marketed for food sensitivities; these can often be highly processed, of low nutritional value and high in sugar, fat and salt
  • Eat as wide a variety of allowed foods as possible
  • Get advice about suitable replacement foods to ensure nutritional requirements are met
  • Consider bottled/filtered water if sensitivities to chemicals in tap water are suspected
  • Reduce dietary and lifestyle stressors, which could exacerbate allergic conditions
  • Exercise to support general health, wellbeing and strong bones
  • Exercise programmes to support specific allergy conditions that affect breathing and the heart
A Nutritional Therapist may also consider dietary strategies to support:
  • Leaky gut-increased permeability of the gut wall
  • Gut inflammation, healing and repair
  • Balanced gut bacteria
  • Cross-reaction between certain food families


1. Brostoff, J. and Gamlin, L. (2008). The complete guide to food allergy and intolerance. 4th ed. Bath: Quality Health Books.

2. Boyce, J.A., Assa’ad, A. and Schwaninger, J. (2010). Guidelines for the diagnosis and management of food allergy in the United States. The journal of allergy and clinical immunology. 126 (6 0), S1-58.