By Dr. Stephanie A. Leonard
Many types of adverse food reactions are often confused with food allergies. Allergists consider a true food allergy to be an abnormal response of the immune system to food protein.
These abnormal responses are mediated by immunoglobulin E antibodies (IgE-mediated) or by immune cells (non-IgE-mediated).
The IgE-mediated food allergies are the kind that may result in immediate hives and swelling or anaphylaxis, a potentially life-threatening reaction with multiple symptoms. Common food allergies in children include allergies to egg, milk, peanut, tree nuts, fish, shellfish, soy and wheat; however, children can develop an allergy to almost any food.
Symptoms develop typically within 30 minutes, but can occur up to two hours after ingestion, and may include hives, lip and/or eye swelling, mouth itching, throat discomfort, coughing, wheezing, difficulty breathing, vomiting, diarrhea and a drop in blood pressure, which may be lead to dizziness or fainting. These symptoms are the result of chemicals, such as histamine, which are released in the body when IgE binds to a particular food protein.
Non-IgE-mediated food allergies typically cause gastrointestinal symptoms. These symptoms may include repetitive vomiting, chronic diarrhea, blood in the stool, weight loss or difficulty swallowing. These gastrointestinal food allergies are often diagnosed either by history alone or with endoscopy by a gastroenterologist.
Food intolerance is a more accurate term when referring to adverse food reactions that do not involve the immune system and are typically not a result of food protein. For example, lactose intolerance is a metabolic disorder where the body does not have the enzyme called lactase to digest the sugar lactose present in cow’s milk. This condition results in bloating, abdominal discomfort and diarrhea. Lactose intolerance is diagnosed by history alone or with a breath test performed by a gastroenterologist. Treatment includes replacement of the enzyme lactase.
Other foods may have a pharmacologic effect due to certain chemicals. This includes sensitivities to chemicals in chocolate, tyramine, aspartame, MSG, nitrates/nitrites, alcohol and caffeine, which may trigger migraines, or symptoms such as fatigue or mood changes in susceptible individuals. These reactions are not life-threatening and there are no tests available to confirm sensitivity. A sensitivity is likely if symptoms disappear when the substance is avoided and reappear when the substance is ingested again.
Adverse food reaction may also be the result of a toxic effect, for example from mishandled or spoiled food. Gastrointestinal symptoms caused by food poisoning may appear similar to those seen in allergic reactions. However, food poisoning reactions often affect more than one individual and symptoms do not occur if the individual eats the food again.
Food allergies are best diagnosed by an allergist to avoid confusion with food intolerance using skin and blood testing. Treatment includes avoiding the trigger food and if IgE-mediated, treating accidental ingestions with antihistamines and injectable epinephrine. New therapies for IgE-mediated food allergy are currently in research.
Dr. Stephanie A. Leonard is a food allergy specialist at Rady Children’s Hospital-San Diego and an assistant professor of pediatric allergy and immunology at UC San Diego.