Allergies and Intolerances Health Article

Allergies and Intolerances

Food allergies affect approximately 3 percent of children and 1 percent of adults in the United States. It is estimated that an even larger percentage of the population experiences problems with food intolerance. Worldwide, adverse reactions to food constitute a significant public health issue.

Definitions

The term adverse reaction is used to describe health problems linked to food. Food allergy and food intolerance are two types of adverse food reactions (food-borne illnesses caused by bacterial, viral, or other forms of contamination are also adverse reactions). A food allergy is said to exist when the health problem is linked to a malfunction of the immune system. It is believed that this malfunctioning occurs when the body identifies a food protein (allergen) as a harmful substance. Food intolerance occurs when the underlying problem causing the adverse reaction is not related to a malfunction of the immune system. One example of a food intolerance is lactose intolerance, a condition affecting people who cannot digest milk due to a deficiency of the enzyme lactase, which breaks down milk sugar (lactose).

Common Foods Associated with Food Allergy

Almost any food can cause an allergy, though the foods most commonly associated with an allergic reaction are those frequently consumed by a population. For example, an allergy to rice is common in Southeast Asia, while fish allergy is a problem in the Scandinavian countries, where fish is frequently consumed (even at breakfast). Age is also a factor influencing the types of foods to which a person might be allergic. In the United States, common foods to which adults are allergic include eggs, shrimp, lobster, peanuts, other nuts, and fish. U.S. children who have food allergies find their problems are most frequently linked to milk, soy, eggs, and peanuts. Infants may be allergic to cow's milk or soy formulas. Some food allergies may be outgrown, but allergies to peanuts, shrimp, and fish tend to last throughout life. In addition, some individuals are only allergic to one food, whereas some are allergic to several foods.

An allergic reaction can be triggered by a very small amount of a food. Persons with food allergies need to read food labels carefully and ask restaurant workers about food ingredients, and the food industry needs to ensure that processed foods are appropriately prepared so that people are not exposed to food allergens unknowingly. This may happen when improperly cleaned food equipment is used to prepare multiple types of food.

Food Allergy

Health problems associated with food allergies can involve the gastrointestinal system, the respiratory system, the skin, and the eyes. Persons with a food allergy may have difficulty breathing, or they may have problems with itching, rashes, swelling, nausea, or vomiting. A food allergy may also be a cause of asthma.

The symptoms of food allergy vary widely from person to person. Food allergies can also cause a severe clinical reaction known as anaphylaxis, which can result in death. Anaphylaxis may be characterized by throat and lip swelling, shortness of breath, sweating, itching, and feeling very faint.

Diagnosis of a food allergy usually involves a careful examination of the patient's symptom history. Other causes of symptoms must be ruled out, and in some instances the suspected food or foods will be eliminated from the diet to see if symptoms stop. Blood tests or skin tests may also be performed. One test sometimes used to diagnose food allergy is the double-blind, placebo-controlled food challenge. This test involves giving a patient a capsule containing a suspected food allergen and a capsule without the allergen (the placebo) and seeing if either causes symptoms in a controlled clinical setting. The test is called double-blind because neither the patient nor the physician evaluating the symptoms is aware of which capsule contains the allergen at the time the testing occurs.

Common Foods Associated with Intolerance

Foods associated with intolerance include: preserved foods, foods containing monosodium glutamate (MSG, a flavor enhancer), and specific foods such as milk, pickled herring, soy sauce, chili peppers, and nutmeg. Intolerance to lactose is a major problem for many populations. In the United States, lactose intolerance is common among those of African and Asian descent. The Native American population also has a high prevalence of lactose intolerance.

For many food intolerances, including those listed above, specific chemicals or enzyme abnormalities have been identified as being associated with the intolerance. Lactose intolerance is associated with problems with the enzyme lactase. Chemicals associated with food intolerance include sulfite (in preserved foods), tyramine (in pickled herring and soy sauce), capsaicin (in chili peppers), and myristicin (in nutmeg).