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Food Allergy Clinic

Diagnosis and Treatment

While an estimated 15 – 20% of Americans have nasal allergies or allergic asthma, only 2% of adults and 8% of children under age six, have adverse reactions (allergic or non-allergic) to foods or food additives. People tend to diagnose themselves, believing they have allergic reactions to certain foods or food ingredients. Unfortunately, self-diagnosis of food allergy often leads to unnecessary food restrictions, nutrient deficiencies, and misdiagnosis of potential life-threatening medical conditions other than food allergy. For reasons that are not completely understood, we do know that food allergies are on the rise nationwide.

Therefore, it is generally agreed that people see a board-certified allergist for proper diagnosis (a board-certified allergist must be board-certified in either internal medicine or pediatrics, and then have two years of additional training in allergy and immunology, and then pass a board certification exam in allergy and immunology).

What is food allergy?

A food allergy is an adverse reaction to a food that involves the body's immune system. A true allergic reaction to a food involves three primary components:

  1. as a food is broken down in the digestive tract, the immune system falsely perceives the digested food as harmful (and so the food becomes "foreign" to the body and is called a food allergen; usually this allergen is a protein);
  2. the immune system then produces an antibody (immunoglobulin E – IgE) specific for that allergen;
  3. when IgE is produced, it attaches to pro-inflammatory cells (mast cells in the tissue and basophils in the blood) which then release histamine and other cell chemicals causing allergic reactions (symptoms are noted in the next paragraph).

What are the symptoms of food allergy?

Symptoms of a true food allergy usually begin as an immediate reaction that occurs within a few minutes to a few hours after eating. Common symptoms include rash, hives, swelling (face, tongue, eyelids and throat), nausea, vomiting, diarrhea, wheezing, asthma, difficulty breathing, and in severe cases, lowered blood pressure that can lead to loss of consciousness. An anaphylactic reaction to a food can be fatal if untreated or undiagnosed.

In children, food allergies may also be manifested as food aversion or changes in behavior or mood.

Delayed allergic reactions (cell-mediated reactions that often do not involve IgE) can cause ongoing skin rashes (eczema), especially in children. Eczema can be caused by both IgE and cell-mediated, non-IgE reactions.

Within the past few years, another type of delayed food reaction has been recognized (allergic eosinophilic esophagitis – EE). EE is usually seen in children or young adults, and most of these individuals have other allergy problems such as nasal allergies and allergic asthma.

In adults, the most common symptoms of EE are dysphagia (difficulty in swallowing solid food), regurgitation of foods, and sometimes acid reflux that does not respond to medicines used to suppress stomach acid production. In children, common symptoms include vomiting, feeling full after eating small amounts of food, abdominal pain, problems with swallowing food, weight loss and failure to thrive. Allergic eosinophilic gastroenteritis can cause many of these same symptoms, but is much less common.

What foods usually cause food allergy?

Allergic reactions can occur with any food or food additive.

In children, foods most likely to cause an allergic reaction are referred to as the "Big 8": peanut, tree nuts (any tree nut such as almond, cashew, walnut, pecan, hazelnut, Brazil nut), fish, shellfish, milk, egg, soy and wheat, although sesame seed and kiwi are being reported with increasing frequency.

Among adults, shellfish, fin fish, peanut and tree nuts are the most common causes of food allergy.

What are adverse food reactions?

Two very common adverse reactions are lactose intolerance (the inability to metabolize lactose, a sugar found in milk and dairy products) and celiac disease (an autoimmune disorder of the small intestine caused from sensitivity to gliadin, a gluten protein found in wheat, barley and rye. It is not the same disease as wheat allergy).

Certain foods can contain large amounts of histamine, and can therefore mimic allergic reactions. Examples of histamine-rich foods include beer and wine, aged or fermented cheeses, mushrooms, vinegar, strawberries and shellfish. Scromboid poisoning occurs when tuna, mackerel, or bonito are caught, but not properly refrigerated before cooking. Bacteria multiply in the fish flesh and convert the naturally occurring histidines to histamines.

Diagnosing food allergy, food intolerance and/or cell-mediated food reactions:

After obtaining a complete medical history, an allergist will generally perform one or more of these tests:

Skin prick test – the most common allergy test measures IgE antibodies in the blood. A small amount of the suspected allergen is placed on the forearm or back, and the skin is gently pricked. If a localized allergic reaction occurs, it will develop within 15-20 minutes, and will cause an itchy red spot with surrounding redness.

Blood test – called a RAST test, it also measures IgE antibodies in the blood. The RAST test is usually not done as a screening test because it is not as sensitive as the prick test, and is considerably more expensive. As a result, many insurance plans will not cover the expense of RAST testing.

Allergy patch test – an allergy test to detect cell-mediated food allergies. Selected foods are placed in special chambers on the back, and secured in place with a special adhesive tape. The food in the chambers are left in contact with the skin for 48 hours and then removed. The patch tests are then read 24 hours later.

When the results of the prick skin test, the RAST test and, if clinically indicated, the allergy patch test are reviewed, the likelihood of identifying the correct allergenic food approximates 85-90%.

Food challenge – when one is dealing with an IgE-mediated reaction, and the history is not clear as to whether the skin test positive food(s) caused the reaction, the doctor may choose to do a food challenge test. You eat the food under strict supervision. After eating the food, you will be monitored to see if a reaction occurs. Because any food challenge could result in a severe allergic reaction, these food challenges should always be done in the doctor's office. Oral food challenge is the most accurate way to diagnose an allergic or adverse reaction to a food.

Elimination diet – the elimination diet involves removing specific foods or ingredients from your diet that you and your doctor suspect may be causing your allergy symptoms. During this time, you will need to carefully read food labels and find out about food preparation methods when eating out. While following this diet, make sure you are eating other foods that provide the same nutrients as those you’ve eliminated. A dietician can help you plan meals that are healthful and nutritious without including the potentially allergenic foods. You will also need to keep a food diary to record the foods you are eating. In general, elimination diets are done over a period of two to four weeks.

Allergy elimination diets that are too restrictive have the potential to cause rickets, iron-deficiency anemia, and impaired growth in children, and osteoporosis due a diary-free diet in adults.

Current treatment of food allergy – once a food allergy has been diagnosed, careful avoidance of that food is mandatory. Although some food allergy in childhood may be outgrown, re-introduction of food must be very carefully done. Some food allergies, like peanut, tree nut and fish are usually a lifelong problem.

In the case of children, parents will need to educate schools, daycare centers, family and friends to the dangers of an allergic reaction. It is recommended that all patients with food allergy carry with them, at all times, self-injectable epinephrine (EpiPen or Twinject), in case of accidental ingestion, and a severe allergic reaction occurs. A rapid acting antihistamine should also be carried by the patient at all times. Asthmatics with food allergies should carry with them a rescue bronchodilator inhaler at all times.

Other treatments for food allergy

Sublingual immunotherapy has been used as a treatment for food allergy in Europe for more than forty years. Because the FDA has not yet approved sublingual therapy (although clinical trials are now underway, essentially replicating the European experience), it is still considered an experimental therapy in the United States.

In Europe, in patients with severe food allergy (anaphylaxis), sublingual immunotherapy may provide some relief from accidental ingestion. Nevertheless, with severe food allergy, very careful avoidance – perhaps life-long for certain foods, especially peanuts, tree nuts and seafood - remains the treatment of choice.

The European experience has shown that in patients with less severe food allergies, sublingual immunotherapy may help liberalize one’s diet, especially if one is allergic to several different foods.

Allergy injections have not been shown to be an effective treatment for food allergy.

A monoclonal anti-IgE antibody similar to Xolair (Xolair is currently approved by the FDA as a treatment for severe asthma) has been shown to lessen the severity of food allergy, but that monoclonal antibody for food allergy has not yet been approved by the FDA.

If you would like our office to help you with your food allergies, please let the receptionist know that you are calling for that problem. Prior to your appointment, we will mail you a Food Allergy Questionnaire. This completed form, along with a detailed interview, will help the doctor obtain an accurate history of your problem at the time of your evaluation.