Define Your Terms

“If you wish to converse with me,” said Voltaire, “define your terms”.

In my practice as an allergy specialist, I find the principle of first defining terms before beginning a discussion with a patient to be key.  Particularly the term “allergy”.   “Allergy” is a very common word, frequently used in general conversation, therefore its definition should be fairly clear.  But this may not always be the case, and subtleties of variance in how we define this term can lead to significant misunderstanding.

From an immunologist’s point of view, a scientific definition of allergy could go something like this:

“Allergy is a  hypersensitivity disorder of the immune system which occurs when a person’s immune system reacts to normally harmless substances in the environment. These reactions are acquired, predictable, and rapid. Allergy is one of four forms of hypersensitivity and is formally called type I (or immediate) hypersensitivity. Allergic reactions are distinctive because of excessive activation of certain white blood cells called mast cells and basophils by a type of antibody called Immunoglobulin E (IgE). This reaction results in an inflammatory response which an range from uncomfortable to dangerous”.

In this definition there are a few key points.  Allergy is reaction to specific substances involving a class of antibodies call IgE,resulting in symptoms.

A more conventional, laymen definition of allergy might look like this:  “An allergy is a reaction of the body to something that you eat, drink, breath or come into contact with that makes you itch, sneeze, wheeze, break out in a rash, get a stomach ache, or swell up”.

There are several medical problems that clearly meet this definition of allergy but in fact, are not allergy at all.  An example of this is lactose intolerance.   This is a problem with mammalian milk (cow, goat, even human) which is caused by the lack of an enzyme which is required to digest milk sugar.    Without this enzyme to turn the big lactose sugar molecule into its much smaller and absorbable bits, drinking milk will cause uncomfortable intestinal bloating, gas, and pain.  Although this a clear reaction to a food, no antibodies are involved,  so it is not an allergy.

Another example is Celiac disease.  In  this rare condition, patients become very ill with abdominal cramping, diarrhea, and even severe weight loss when exposed to even small amounts of gluten in their diet.  This difficult condition is definitely caused by an antibody reaction to a particular food, although the antibody is IgA, not IgE, and is therefore by definition, not an allergy.

Allergy has also been defined in terms of a result on a laboratory test  as well as in terms of symptoms.  For example, if a patient has a laboratory blood test that looks for IgE antibodies to food, any positive result might be viewed as proof of a food allergy.   However,  our definition of  allergy also  requires the presence of symptoms.     When a patient shows evidence of IgE antibodies to a food on an allergy test, we use the term “sensitization”.    A blood test for food allergy may show multiple sensitivities, but unless there is a history of adverse symptoms caused by a particular food, there is no allergy.    This means that you could be “sensitized” to something without being “allergic”, but you cannot be allergic if you are not sensitized.   Essential to the diagnosis of food allergy is the presence of symptoms caused by exposure to a food and laboratory evidence (skin test or blood test) of anti-food IgE antibodies.

Sensitivity, the antibody response on a laboratory test for allergy,  is an important definition to keep in mind when we discuss other tests for food allergy, such as the IgG test.  This test is commonly used in Naturopathic  Medicine, a form of alternative medicine, that places a strong emphasis on the role of diet  and food allergy in health and well being. IgG, like IgE, is a class of antibodies produced by our immune system.  Unlike IgE, IgG’s primary job is to defend against infections such as viruses and bacteria.  When you get a flu shot you are boosting the bodies production of anti-flu virus IgG antibodies.  When the real flu tries to invade and make you sick, the anti-flu IgG antibodies are ready to squash them.    Results of these IgG tests for food allergy frequently return a long list of positive reactions, and patients, upon seeing this list, frequently ask the question, “so what am I supposed to eat if I am allergic to all these foods”.

It does seem strange that our bodies would produce antibodies to a food if there is not a problem of some kind. Why would our immune system react to a food unless it had an issue with it, even if I am not aware of a problem or what that issue is?  Naturopaths use this line of reasoning to suggest that some foods cause “hidden allergy” and can be a source of inflammation.  This inflammation could lead to a variety of chronic conditions such as fatigue, headaches, weight gain, depression, mental fogginess, and many others.  However, this assumption is often a misunderstanding.  Some experts believe that the IgG antibody response occurs to the foods we eat the most and may play a role in the proper development of tolerance.  Tolerance is a good thing. Therefore the IgG food allergy test may simply reflect the foods that we eat most commonly, rather than being harmful.  For this reason, most experts agree that the IgG test for food  allergy is unhelpful and may in fact lead to excessive and dangerous food restriction diets.