• Section 2. Food Allergy Categories

    Section Summary

    The following topics are included in this section:

    • Food allergy categories
    • Food allergy and food intolerance differences


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    Food Allergy Categories

    The National Institute of Health reports that a food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.  Food allergens are the parts of food or ingredients within food (usually proteins) that are recognized by immune cells. When an immune cell binds to a food allergen, a reaction occurs that causes the symptoms of food allergy.1

    Most food allergens cause reactions even after they have been cooked or digested. Some allergens, most often from fruits and vegetables, cause allergic reactions only when eaten raw. Food oils, such as soy, corn, peanut, and sesame, may or may not be allergenic (causing allergy), depending on how they are processed. “Allergy” and “allergic disease” refer to conditions that involve changes to your immune system. These immune system changes fall into two categories:

    1. Immunoglobulin E (IgE) mediated - the symptoms are the result of interaction between the allergen and a type of antibody known as IgE, which is thought to play a major role in allergic reactions

    2. Non-IgE-mediated - the symptoms are the result of interaction of the allergen with the immune system, but the interaction does not involve an IgE antibody

    If a person is sensitized to a food allergen, it means that their body has made a specific IgE (sIgE) antibody to that food allergen, but they may or may not have symptoms of food allergy.

    If a person can consistently tolerate a food that once caused them to have an allergic reaction, they have outgrown the food allergy.2

    Food Allergy and Food Intolerance Differences

    Food allergy is sometimes confused with food intolerance. Food intolerances are adverse health effects caused by foods. They do not involve the immune system. For example, if a person is lactose intolerant, they are missing the enzyme that breaks down lactose, a sugar found in milk.3

    Lactose Intolerance

    Lactose is a sugar found in milk and most milk products. Lactose is an enzyme in the lining of the gut that breaks down or digests lactose. Lactose intolerance occurs when lactase is missing. Instead of the enzyme breaking down the sugar, bacteria in the gut break it down, which forms gas, which in turn causes symptoms of bloating, abdominal pain, and sometimes diarrhea.

    Lactose intolerance is uncommon in babies and young children under the age of 5 years. Because lactase levels decline as people get older, lactose intolerance becomes more common with age. Lactose intolerance also varies widely based on racial and ethnic background.

    A healthcare professional can use laboratory tests to find out whether the person’s 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, add color, or protect against the growth of microbes. Compounds such as monosodium glutamate (MSG) and sulfites are tied to reactions that can be confused with food allergy.

    MSG is a flavor enhancer. When taken in large amounts, it can cause some of the following:

    • Flushing
    • Sensations of warmth
    • Headache
    • Chest discomfort

    These passing reactions occur rapidly after eating large amounts of food to which MSG has been added. Sulfites are found in food for several reasons:

    • They have been added to increase crispness or prevent mold growth.
    • They occur naturally in the food.
    • They have been generated during the winemaking process.
    • Sulfites can cause breathing problems in people with asthma.

    The FDA has banned sulfites as spray-on preservatives for fresh fruits and vegetables. When sulfites are present in foods, they are listed on ingredient labels.

    Gluten Intolerance

    Gluten is a part of wheat, barley, and rye. Gluten intolerance is associated with celiac disease, also called gluten-sensitive enteropathy. This disease develops when the immune system responds abnormally to gluten. This abnormal response does not involve IgE antibody and is not considered a food allergy.

    Food Poisoning

    Some of the symptoms of food allergy, such as abdominal cramping, are common to food poisoning. However, food poisoning is caused by microbes, such as bacteria, and bacterial products, such as toxins, that can contaminate meats and dairy products.

    Histamine Toxicity

    Fish, such as tuna and mackerel that are not refrigerated properly and become contaminated by bacteria, may contain very high levels of histamine. A person who eats such fish may show symptoms that are similar to food allergy. However, this reaction is not a true allergic reaction. Instead, the reaction is called histamine toxicity or scombroid food poisoning.

    Other Conditions

    Several other conditions, such as ulcers and cancers of the gastrointestinal (GI) tract, cause some of the same symptoms as food allergy. These symptoms, which include vomiting, diarrhea, and cramping abdominal pain, become worse when you eat.


    Section 1. Course ObjectivesSection 3. Prevalence of Food Allergies