If someone reacts to food, they may have a Food Hypersensitivity (FHS). FHS reactions involving the immune system are known as food allergy (FA). There are two main types of food allergy; IgE mediated allergy where reactions generally occur within 30 minutes of eating the food and immune reactions to food which can occur over 2 hours after eating the food which are called Non-IgE mediated food allergies. There are different sub-types of Non-IgE mediated food allergy eg Food Protein Induced Enterocoloitis syndrome (FPIES) and Eosinophilic Eosophagitis (EoE). Other reactions to food may be due to an intolerance ( eg lactose intolerance) or a food hypersensitivity (e.g salicylate hypersensitivity.
IgE-mediated Food Allergy
Between 6-8% of children and up to 4% of adults suffer from an IgE Mediated food allergy. This occurs when the immune system develops antibodies against certain food proteins, known as allergens. These antibodies then cause reactions when they come into contact with the food protein. Reactions usually involve itching or swelling of the mouth/throat and itchy rashes and/or hives like insect bites. Wheezing, hay fever, eczema and flushing can also occur.
Symptoms can be severe and include life-threatening anaphylaxis. IgE mediated food allergy in adults is often linked to hay fever in the spring and/or summertime. This condition is known as Pollen Food Syndrome (PFS), previously called Oral Allergy Syndrome, and involves immediate symptoms, typically itching of the lips, mouth and ears, triggered by a cross-reaction between the pollen antibodies and plant food proteins. Adults can also experience another type of IgE mediated allergy to plant proteins called Lipid Transfer Protein (LTP) Allergy. Differentiating between PFS and LTP allergy requires the involvement of an experienced allergist.
Non-IgE mediated food allergy
The two most widely recognised Non IgE mediated food allergies are FPIES and EoE.
FPIES is most commonly seen in infants and young children but it is being seen more commonly in adults. The main symptoms are vomiting and diarrhoea although in adults, vomiting is less common. Symptoms occur from 1 -6 hours after eating the causative food which most commonly are milk, wheat (children) and fish and shellfish (adults).
EOE is seen in older children, teenagers and adults. Symptoms in children are usually reflux, picky eating, stomach aches and poor weight gain. Adults normally present to their GP with increasing symptoms of swallowing difficulty or attend the hospital emergency department with food “stuck”. Other presentations may be less specific such as heartburn, reflux or generalised chest pain. The most common trigger foods are milk and wheat although other foods may cause symptoms such as egg or fish.
Infants and young children presenting with symptoms such as colic, vomiting, diarrhoea may have a non-IgE allergy and this is usually related to milk. However, as infants and young children may have these symptoms without having a food allergy, it is important that any diagnosis is correct by undertaking the two-step process of eliminating the suspect food, then reintroducing to see if the symptoms return.
Non-Allergic Food Hypersensitivities
There are two main types of non-allergic food hypersensitivity; food chemical hypersensitivity and food intolerance
Food chemical hypersensitivity.
This is when symptoms after eating a food are due to pharmacological or chemical sensitivities. They can be difficult to diagnose due to the wide range of natural and added chemicals in foods, varying symptoms and individual tolerance levels. Naturally present food “chemicals” which may be implicated include histamine and other vasoactive amines, salicylates and benzoates. Added food chemicals include sulphites and benzoates.
Investigating whether symptoms may be due to a food chemical hypersensitivity is usually done by complete avoidance of the suspected food “chemical” for no longer than 3-4 weeks, to see if symptoms resolve. Since symptoms usually only occur if intake of the relevant food “chemical” exceeds the individual’s tolerance threshold, complete avoidance is not required.
Food Intolerance
The term Food intolerance is widely used by the general public when describing unpleasant symptoms after eating certain foods. They may be used incorrectly to describe Non-IgE mediated allergy or a food chemical hypersensitivity.
Food intolerance symptoms are usually associated with the gut and can include Irritable Bowel Syndrome (IBS) symptoms and reflux. As with food chemical hypersensitivity, symptoms usually occur if intake is above the individual tolerance level so complete avoidance is not usually required. The commonest type of intolerance would be to lactose which affects people who cannot produce enough of the enzyme required to digest milk sugar. Some people can have a fructose intolerance where they get gastrointestinal symptoms after eating large amounts of fruit. In IBS, up to 70% of sufferers report symptoms to specific foods which may include onions and garlic.
Foods Involved
The commonest foods causing food allergy are milk, egg, and peanuts, sesame seeds, kiwi fruit, fish, shellfish, tree nuts, wheat and soy. All of these foods (except for kiwi) have to be labelled if present or added to any food however small the amount. A variety of fruits, vegetables or nuts can cause PFS, but the commonest triggers are apples, stone fruits (peaches, plums etc), hazelnuts and almonds. Milk and wheat are the foods most often reported to cause symptoms of food intolerance and for food chemical hypersensitivity it can be certain types of fruits and vegetables or processed foods such as cheeses and meats.
Diagnosis
Food Allergies are best diagnosed by a specialist who can use tests to detect the presence of IgE. For other reactions to foods there are no reliable diagnostic tests (apart from oesophageal biopsy for EoE) so diagnosis is via food elimination and re-introduction. This should be done with the support of a specialist experienced in managing this process and who is able to assess the resultant diet meets all nutritional needs.
An expert assessment of the diet is essential for all children on food avoidance diets, and also for adults who are excluding milk or wheat. People with IgE mediated Food Allergy should also always carry their prescribed medication with them and know when and how to take it. Some children will grow out of an food allergy, so teenage or young adults with an FA diagnosed in childhood should be reviewed.
FI is commonly reported; about 20% of the population alter their diet because they believe they have a reaction to food. However, the numbers who actually have FI are likely to be much lower. FI does not involve the immune system; symptoms are usually less severe than those in FA and may occur hours or days after the food was eaten. The commonest type of FI is lactose intolerance which affects people who cannot produce enough of the enzyme required to digest milk sugar. FI may be linked to other conditions; about 70% of people with irritable bowel syndrome report symptoms to specific foods.
The commonest foods causing FA are milk, egg, and peanuts, sesame seeds, kiwi fruit, fish, shellfish, tree nuts, wheat and soy. All of these foods (except for kiwi) have to be labelled if present or added to any food however, small the amount. A variety of fruits, vegetables or nuts can cause OAS, but the commonest triggers are apples, stone fruits (peaches, plums etc), hazelnuts and almonds. Milk and wheat are the foods most often reported to cause symptoms of FI.
FA and FI are best diagnosed by a specialist. For FA, tests measuring levels of food IgE antibodies may be useful, although a positive result may not mean the person is allergic to that food. There are currently no reliable tests to diagnose FI except when lactose intolerance is suspected. Once diagnosed, the only current treatment for FA or FI is avoidance of the known food trigger(s). Anyone with suspected or diagnosed FA or FI, who has cut out foods from their diet, needs to make sure their diet is not nutritionally unbalanced.
An expert assessment of the diet is essential for all children on food avoidance diets, and also for adults who are excluding milk or wheat. People with FA should also always carry their prescribed medication with them and know when and how to take it. Some children will grow out of an FA, so teenage or young adults with an FA diagnosed in childhood should be reviewed.