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There are many reasons why particular foods may not agree with us. Many North Americans believe the reason for their food-related symptoms is an allergy to a particular food or ingredient. But in the vast majority of cases, a bona fide food allergy is not the cause of the problem.

Classic food allergies occur in only about 2 percent of adults. Children have a higher incidence of food allergies (estimated at about 6 percent), but the majority of adverse reactions to foods are not true allergies.

What is a Food Allergy?

Allergies are caused by exaggerated immune reactions unrelated to injury or infection. There are four types of hypersensitivity reactions, and a typical allergic reaction may involve more than one type.

Classic food allergies are mediated by substances called immunoglobulins (primarily immunoglobulin E, or IgE). When a foreign protein from food binds to IgE, a series of events is triggered, including the release of such chemicals as histamine and inflammatory mediators. These mediators cause blood vessels to dilate, more mucus to be secreted, airways to constrict, and various additional reactions within the skin.

Histamine is responsible for many of the symptoms that occur as part of an allergic reaction. It is contained within mast cells; when IgE binds to these cells, they burst open, releasing histamine and triggering a classic allergic reaction.

The most common foods to which people are allergic are dairy, wheat, soy, eggs, peanuts, shellfish, and tree nuts.

Symptoms of a classical food allergy may include itching of the skin followed by hives (a rash of raised, reddish bumps or welts), swelling of the lips and mouth, abdominal cramps, nausea, vomiting, or diarrhea. Skin testing or RAST (radio-allergosorbent test) can often help identify the allergen.

What is Food Intolerance?

Food intolerance refers to symptoms caused by an inability of the digestive system to properly process a particular food, causing irritation. The classic example of food intolerance is lactose intolerance, which is caused by a hereditary or acquired deficiency of the enzyme lactase, which is responsible for digesting milk sugar.

Food intolerance is not caused by the immune system. The amount of food eaten with food intolerance often correlates to the severity of the symptoms. A lactose-intolerant person who drinks only a tiny amount of milk is likely to have only mild symptoms, whereas the person with a milk allergy who drinks the same tiny amount of milk could theoretically have a full-blown anaphylactic reaction.

Hidden Food Allergies or Food Sensitivities

There is another type of allergic reaction that is not as well recognized as the classical allergic reaction: the hidden allergy. A classic allergic reaction to a food is usually obvious, and usually not as severe as anaphylaxis. Hidden allergies are not as well accepted or understood.

But hidden allergies may be more common than most doctors think. They are not easy to diagnose. A person with hidden allergies may not even suspect that food is at the root of their fatigue or other health problems.

The relationship between eating a particular food and the development of a symptom is not always clear: the symptoms may be delayed, even by days. Also, the reaction may not occur every time the food is eaten, but may instead occur when food is cooked in a particular way, or is eaten with other problematic foods. Skin tests and RAST are next to useless for identifying hidden allergies.

Both classic and hidden food allergies can cause fatigue, depression, anxiety, and other mental or emotional symptoms. Headaches, sinusitis, recurrent infections, and skin problems are also quite common. In the early stages of a hidden food allergy, the food triggers obvious symptoms, such as a skin rash or nasal congestion.

Jeremy Appleton, ND, CNS, is a licensed naturopathic physician and certified nutrition specialist.

Source: alive #313, November 2008