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Food Allergy or Food Intolerance?

If you go to your health care provider and say, "I think I have a food allergy," your provider has to consider other possibilities that may cause symptoms and could be confused with food allergy, such as food intolerance. To find out the difference between food allergy and food intolerance, your provider will go through a list of possible causes for your symptoms. This is called a "differential diagnosis." This type of diagnosis helps confirm that you do indeed have a food allergy rather than a food intolerance or other illness.

Types of Food Intolerance

Food poisoning
One possible cause of symptoms like those of food allergy is foods contaminated with microbes, such as bacteria, and bacterial products, such as toxins. Contaminated meat and dairy products sometimes cause symptoms, including GI discomfort, that resemble a food allergy when it is really a type of food poisoning.

Histamine toxicity
There are substances, such as histamine present in certain foods that cause a reaction like an allergic reaction. For example, histamine can reach high levels in cheese, some wines, and certain kinds of fish such as tuna and mackerel. In fish, histamine is believed to come from contamination by bacteria, particularly in fish that are not refrigerated properly. If you eat one of these foods with a high level of histamine, you could have a reaction that strongly resembles an allergic reaction to food. This reaction is called "histamine toxicity."

Lactose intolerance
Another cause of food intolerance confused with a food allergy is lactose intolerance or lactase deficiency. This common food intolerance affects at least one out of ten people.

  • Lactase is an enzyme that is in the lining of the gut.
  • Lactase breaks down lactose, a sugar found in milk and most milk products.
  • There is not enough lactase in the gut to digest lactose.
  • Lactose, instead, is used by bacteria to form gas which causes bloating, abdominal pain, and sometimes diarrhea.

There are tests your health care provider can use to find out whether your body can digest lactose.

Food additives
Another type of food intolerance is a reaction to certain products that are added to food to enhance taste, provide color, or protect against the growth of microbes. Several compounds, such as MSG (monosodium glutamate) and sulfites, are tied to reactions that can be confused with food allergy.

  • MSG
    MSG is a flavor enhancer, and, when taken in large amounts, can cause some of the following signs:
    • Flushing
    • Sensations of warmth
    • Headache
    • Chest discomfort
    • Feelings of detachment

    These passing reactions occur rapidly after eating large amounts of food to which MSG has been added.

  • Sulfites
  • Sulfites occur naturally in foods or may be added to increase crispness or prevent mold growth. Sulfites in high concentrations sometimes pose problems for people with severe asthma. Sulfites can give off a gas called sulfur dioxide that the asthmatic inhales while eating the sulfited food. This irritates the lungs and can send an asthmatic into severe bronchospasm, a tightening of the lungs. The Food and Drug Administration (FDA) has banned sulfites as spray-on preservatives in fresh fruits and vegetables. Sulfites are still used in some foods, however, and occur naturally during the fermentation of wine.

Gluten intolerance
Gluten intolerance is associated with the disease called 'gluten-sensitive enteropathy" or "celiac disease." It happens if your immune system responds abnormally to gluten, which is a part of wheat and some other grains.

Psychological causes

Some people may have a food intolerance that has a psychological trigger. If your food intolerance is caused by this type of trigger, a careful psychiatric evaluation may identify an unpleasant event in your life, often during childhood, tied to eating a particular food. Eating that food years later, even as an adult, is associated with a rush of unpleasant sensations.

Other causes
There are several other conditions, including ulcers and cancers of the GI tract, that cause some of the same symptoms as food allergy. These problems include vomiting, diarrhea, and cramping abdominal pain made worse by eating.

Exercise-Induced Food Allergy
At least one situation may require more than simply eating food with allergens to start a reaction: exercise-induced food allergy. People who have this reaction only experience it after eating a specific food before exercising. As exercise increases and body temperature rises, itching and lightheadedness start and allergic reactions such as hives may appear and even anaphylaxis may develop. The cure for exercised-induced food allergy is simple, avoid eating for a couple of hours before exercising.

Common Food Allergies

In adults, the foods that most often cause allergic reactions include:

  • Shellfish such as shrimp, crayfish, lobster, and crab
  • Peanuts
  • Tree nuts such as walnuts
  • Fish
  • Eggs

The most common foods that cause problems in children are:

  • Eggs
  • Milk
  • Peanuts

Tree nuts and peanuts are the leading causes of deadly food allergy reactions called anaphylaxis.

Adults usually keep their allergies for life, but children sometimes outgrow them. Children are more likely to outgrow allergies to milk or soy, however, than allergies to peanuts or shrimp. The foods to which adults or children usually react are those foods they eat often. In Japan, for example, rice allergy is more frequent. In Scandinavia, codfish allergy is more common.

Source: National Institute of Allergy and Infectious Diseases
NIH Publication No. 04-5518 July 2004

Adapted by Editorial Staff, June 2007
Last update, August 2008



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