When someone has a reaction to foods that are harmless for most people, the person is having a “hypersensitivity” reaction. When everyone who eats that food has a reaction (e.g food poisoning) it is called a “toxic” reaction.
Many people think the terms food allergy and food intolerance mean the same thing; however, they do not. “Food intolerance” is a hypersensitivity reaction that does not involve the immune system. Food intolerance is a digestive system response rather than an immune system response. It occurs when something in food irritates a person’s digestive system or when a person is unable to properly break down the food.
A food allergy is a reaction that involves the immune system. The difference is important because food allergy can range from mild reactions to severe, life threatening (anaphylactic) reactions and can occur even with tiny doses. Food intolerances are not life threatening and the person may be able to eat small amounts of the food, but have symptoms on eating larger amounts.
How common is true food allergy?
There are two main groups of food allergy
- Immediate-type (IgE-mediated) food allergies which are more common
- Delayed type (non-IgE-mediated) food allergies which are less common
These types of allergies present quite differently as they have very different underlying mechanisms (See what is an allergy).
Immediate allergies occur most commonly to:
- Hen’s egg
- Peanuts and other nuts
Immediate-type (IgE-mediated) food allergy
This is the most common type of food allergy. Reactions occur from minutes up to 2 hours after eating the food.
Some people react to tiny amounts whereas others react to larger amounts. The amount varies between people but also may vary within the same person on different occasions.
People with very severe allergies may react with tiny doses that contaminate another food, or that they come into contact with by being kissed by someone who has just eaten the food or by food particles in the air when someone is cooking that food!
Immediate (IgE mediated) allergy may cause:
Itchy skin, a red rash, flushing and swelling of the skin around the eyes or other parts of the body.
- Swollen, watering or itchy eyes
- Swelling of the lips or tongue, vomiting, diarrhoea or abdominal cramps
- Sniffing and sneezing, wheezing or asthma attacks, noisy or difficult breathing
- Anxiety, children being withdrawn and a “feeling of doom”
- Fast heartbeat, low blood pressure, fainting or collapse
When the circulation or the airway is involved, the allergic reaction is severe, known as anaphylaxis (pronounced an-a-fi-LAK-sis). This can occur very quickly and is a medical emergency.
Delayed type (Non IgE mediated) food allergy
This type of allergy is less common than immediate type food allergy. It occurs hours to days after eating the offending food and is often more difficult to recognize. (See delayed food allergy).
People who are allergic to one food may react to a similar protein found in something else. For example, people who are allergic to peanuts are often allergic to tree nuts or sesame. Some people with hayfever from tree, grass or weed pollens may develop reactions to certain fruits or nuts.
This is known as cross-reactivity. Cross-reactivity happens when the immune system thinks one protein is closely related to another.
How is food allergy diagnosed?
If a reaction occurs every time a food is eaten it is more likely to be a true (especially immediate type) food allergy. Diagnosing food allergy rests on careful evaluation of the patient together with test results.
In immediate type allergies, skin prick tests or blood tests (which detect IgE antibodies to various foods in the blood) may be very useful (See skin prick testing). However it is critical to remember that a “positive” skin or blood test does not necessarily mean the person is allergic … this may occur when someone is “sensitized” to the food and has some antibodies, but is able to eat the food in any case because other mechanisms in the body are making them tolerant.
If the diagnosis is uncertain an “oral food challenge” may be necessary. In an oral food challenge, increasing amounts of the food are given under close supervision in a clinic or hospital. The person will either “fail” the challenge by having a reaction, or will “pass” the challenge by being able to eat a full age-appropriate portion. This is sometimes to only way to check whether someone is truly allergic to a food (see oral food challenges).
There is absolutely no evidence that ALCAT, Vega testing, pulse testing or kinesiology are of any benefit in diagnosing food allergy. People who use these tests may spend a lot of money to receive an incorrect list of foods to avoid and risk their nutrition.
How is food allergy treated?
At the moment, there is no “cure” for food allergies. People with an allergy need to avoid that particular food (or foods). They must read all food labels and understand the scientific words for the foods in case they are not labelled clearly.
At the same time it is essential to provide a balanced diet with enough protein, energy, minerals and vitamins. A qualified dietician may be able to guide you on how to ensure this.
For immediate-type reactions the patient must know how to recognise and treat an allergic reaction, in case they accidentally eat this food. To help them, AFSA has an emergency action plan that details how to recognise a reaction and how to treat it. (See anaphylaxis action plan)
For milder reactions, just an antihistamine is given. However for more severe reactions, a dose of adrenaline given by injection into a muscle can be life-saving. The doctor will advise if the patient are at risk of severe reactions and whether they need an adrenaline pen.
Patients with food allergy must see a doctor with experience in food allergies regularly. The doctor will check whether they are managing to avoid the food, whether accidental reactions are being treated properly, whether the risk of severe reactions has changed and whether there are signs that the allergy may be outgrown. If the doctor thinks there is a chance of the allergy being out grown s/he may repeat skin or blood tests and then do an oral food challenge test.
Non-allergic food intolerances
There are different types of non-immune reactions to food.
Some people with food intolerance will tolerate small amounts of a certain food, only to become symptomatic if they have too much of it, for example wheat in people with irritable bowel syndrome.
Some people may lack the enzymes to digest certain foods. The commonest example is lactose intolerance where the “lactase” enzyme used to break down milk sugar lactose is missing. This causes cramping and diarrhoea after eating dairy products.
Non-allergic food intolerance may also be caused by preservatives, flavouring agents such as monosodium glutamate (MSG), colouring agents such as tartrazine and preservatives such as sulphur dioxide and benzoates.