Food Allergy vs. Food Intolerance

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Is there a difference between a food allergy and a food intolerance?
I get asked this question quite a lot actually and it is a great question.
The answer can be quite easy or quite involved; basically yes there is a big difference between the two.


Allergy refers to a response of the immune system. It involves immunological processes similar to (but not exactly the same as) those that fight and reject an agent that can cause diseases, such as a pathogenic (disease-causing) micro- organism.

Hypersensitivity is the term scientists use to describe the immunological process that results in allergy. The terms allergic reaction and hypersensitivity reaction are often used interchangeably.

Food Intolerance refers to a reaction that does not involve the immune system. It is caused by a problem in the way the body processes the food or food additive. The term food intolerance is not interchangeable with either food allergy or hypersensitivity.


Food sensitivity is a rather non- specific term that refers to a person’s reacting adversely to a food or component of the food when it is not clear whether the reaction is due to allergy or intolerance. The term food sensitivity is therefore interchangeable with either food allergy or food intolerance, but it does not give any indication of the reason for a person’s symptoms.

Food sensitivities can affect any organ system in the body. Fatigue, anxiety, depression, insomnia, obesity, ear infections, post nasal drip, irritable bowel syndrome, diarrhea, Chrohn’s disease, high blood pressure, eczema, hives, muscle aches, headaches, migraines and asthma are some of the symptoms due to food allergy.

Allergy Types
Our immune system can produce symptoms simply as a result of our ingesting food; this is known as a food allergy. Food allergies are classified into four types:
1- Anaphylactic
2- Cytotoxic
3- Antigen-antibody complexes
4- Delayed hypersensitivity

There are two types of allergic reaction: fixed and cyclic. Fixed reactions are IgE mediated and are easily recognized. If you eat a particular food and immediately get sick or break out, you know what food is triggering the reaction, especially if it happens every time you eat that specific food. Cyclic or delayed food allergy is hard to detect. Sometimes the reaction can be delayed and symptoms appear hours or days later. It is estimated that only five percent of food allergy is immediate and ninety-five percent is delayed.

Type I Reactions
Anaphylaxis is usually IgE mediated. In this instance, the body manufactures an antibody when a foreign substance ( an antigen) gains access to the intestines, lung or skin.

An anaphylactic reaction is fixed and can vary from mild to fatal, but usually appears within minutes of ingestion of the food. It can affect respiratory tract ( bronchial obstruction, wheezing), the gastrointestinal tract ( nausea, vomiting, bloating, or diarrhea), the cardiovascular system ( hypotension and shock), and the skin ( hives). Sensitivity to the food usually persists for more than two years, even after the food is removed from the diet; therefore, the only treatment for this is elimination of the offending food.

Type II and Type III Reactions
Cytotoxic reactions (type II) involve IgE or IgM mediated responses and are cyclic in nature. IgG and IgM are antibodies that are made to defend our immune system. Unlike a fixed food allergy, a cyclic allergy is exposure dependent. Therefore, the more frequently a sensitive food is ingested, the greater the IgG reaction, which leads to increased sensitivity. Treatment for this type of allergy is to eliminate the food for six months, then reintroduce it to the diet, but not eat it every day. The reason for eliminating the food for six months is so the IgG falls to a low level. When the food is reintroduced, there will be a slight elevation of IgG, but limited exposure will keep the IgG low, therefore not producing allergic symptoms. Doctors suggest a rotation diet in which the suspected food is eaten only every four days. Infrequent exposure to this food ensures that IgG reactions will not become elevated and reactive symptoms high. Type III reactions are when antigen-antibody complexes are formed in the blood. Symptoms are not always immediate and can be delayed, therefore not always relating to food ingestion. Like type I, they are difficult to diagnose.

Type IV Reactions
These are cell mediated immune reactions, which are triggered by the interaction between actively sensitized lymphocytes and specific antigens. These types of cyclic reactions can be the most difficult to diagnose, as the T-cell effect develops twenty-four to seventy-two hours after the ingestion of the antigen, so it is difficult to say which food is causing the reaction.
Skin tests and IgE Rast tests will not detect these, so doctors often tell people that they do not have food allergies when in fact they do.

There are many ways of testing for food allergies. Stay tuned for my next blog entry which will describe the different ways of testing for food allergies.