Food Intolerance

How Food Intolerance is Different From Food Allergy

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There are differences between food allergy and food intolerances.. Jon Feingersh/Blend Images/Getty Images

Approximately 4% of all people suffer from food allergies, but many more people have adverse reactions to foods that don’t represent a true allergy. These people actually suffer from food intolerance, which represents a cause-and-effect relationship between eating a certain food and having symptoms, but an allergic reaction doesn’t occur. A true food allergy involves the presence of allergic antibody (IgE) against the food, which causes the release of chemicals (such as histamine) from allergic cells (such as mast cells and basophils).

Symptoms of Food Allergy Versus Food Intolerance

With a true food allergy, most people experience symptoms within 20 to 30 minutes of eating the trigger food. Skin symptoms (itching, urticaria, angioedema) are the most common, and occur during almost all food reactions. Other symptoms can include nasal (sneezing, runny nose, itchy nose and eyes), gastrointestinal (nausea, vomiting, cramping, diarrhea), respiratory (shortness of breath, wheezing, coughing, chest tightness), and vascular (low blood pressure, light-headedness, rapid heart beat) symptoms. When symptoms involve the skin and at least one other organ system, the reaction is called anaphylaxis, and can be life-threatening.

Symptoms of food intolerance can be wide-ranging, and most often include gastrointestinal symptoms, but may include headaches, mood or behavioral changes, and certain skin symptoms. While there may be a direct relationship between consuming the food and symptoms that occur, there is no allergic antibody present against the food.

Diagnosis of Food Intolerance

Unlike food allergy, which is diagnosed with the use of allergy testing, there is typically no test available to diagnose food intolerance. Food intolerance is most often diagnosed clinically, meaning that symptoms are not consistent with food allergy, so no allergy testing is needed.

If allergy testing is performed, the results will be negative with food intolerance. The exception to this is with lactose intolerance, where various tests are available, but most physicians make the diagnosis based only on a person's symptoms.

Examples of Food Intolerance

Food intolerance can be classified as toxic and non-toxic. Toxic reactions would be expected to occur in most people if enough of the food was eaten. Examples include alcohol intolerance, caffeine intolerance, or food poisoning. These reactions would be expected to affect just about anyone, if enough of the food is consumed.

One form of food poisoning, called scombroid, involves eating spoiled fish containing large amounts of histamine. The symptoms of scombroidosis are virtually identical to symptoms of true food allergy, although allergy testing is negative, since no allergic antibody is present.

Non-toxic food intolerance occurs only in certain people, such as lactose intolerance, which is due to the deficiency of lactase, the enzyme that breaks down the sugar in milk and dairy foods.

Patients with lactose intolerance experience bloating, cramping and diarrhea within minutes to hours after eating lactose-containing foods, but do not experience other symptoms of food allergies.

Other examples of non-toxic food intolerances include monosodium glutamate (MSG), which results in a flushing reaction commonly referred to as Chinese Restaurant Syndrome. Strong odors and smells emitted from certain foods trigger adverse reactions in some people, and some people with irritable bowel syndrome or migraine headaches relate worsening of their symptoms with consumption of certain foods.

How Food Intolerance is Treated

The treatment of food intolerance simply involves the avoidance of the trigger food. In most cases, no other treatment or cure is available, except in the case of lactose intolerance. People who suffer from lactose intolerance may use a lactase replacement product, or use dairy products that have the lactose sugar already broken down. Lactaid® is an example of one brand that offers these different products.

Food intolerance cannot result in anaphylaxis, except in the case of scromboidosis, so the availability of injectable epinephrine isn’t needed.


The American Academy of Allergy, Asthma and Immunology, and Food Allergy Practice Parameters. Ann Allergy Asthma Immunol. 2006; 96:S1-68.

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