Food Allergy or Food Intolerance?

If you go to your healthcare 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 food 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 the powerful chemical histamine, present in certain foods that cause a reaction similar to 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 1 out of 10 people.

Lactase is an enzyme that is in the lining of your gut. Lactase breaks down or digests lactose, a sugar found in milk and most milk products.
Lactose intolerance, or lactase deficiency, happens when there is not enough lactase in your gut to digest lactose. In that case, bacteria in your gut use lactose to form gas which causes bloating, abdominal pain, and sometimes diarrhea.

Your healthcare provider can use laboratory tests 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 chemical compounds, such as MSG (monosodium glutamate) and sulfites, are tied to reactions that can be confused with food allergy.

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 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 a person with asthma inhales while eating food containing sulfites. This gas 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. Some researchers include celiac disease as a food allergy. This abnormal immune system response, however, does not involve IgE antibody.

Psychological causes

Some people may have a food intolerance that has a psycho­ logical 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 symptoms include vomiting, diarrhea, and cramping abdominal pain made worse by eating. Diagnosis