The prevalence of food allergies has been increasing in recent years, and it is now estimated to be 6-8% in children and 3-5% in adults. Food allergies are the result of the body’s immune response to food proteins. People with food allergies produce specific IgE antibodies, that when exposed to the allergic food, result in an allergic reaction of varying severity.
Typical non-life threatening reactions to food allergies include hives, flushing, vomiting and lip, face or tongue swelling, which usually occur within an hour of ingesting the allergenic food. These reactions are treated successfully with an oral antihistamine, such as diphenhydramine or cetirizine.
More severe life-threatening reactions to foods involve anaphylaxis, which includes feelings of lightheadedness or dizziness from dropping blood pressure, throat swelling, coughing, wheezing and shortness of breath. These reactions need to be treated with epinephrine.
It is recommended that all patients with food allergies carry an epinephrine autoinjector with them at all times, and also keep one at work or school. It has been shown that previous reactions do not predict future reactions. This means that someone who has never had anaphylaxis to a certain food can still have anaphylaxis to that food if ingested in the future. Vice versa, someone who had an anaphylactic reaction to a certain food may not have anaphylaxis if that same food were ingested again.
What are the main food allergens?
There are 8 main foods that are considered to cause a majority of food allergic reactions. These are peanuts, tree nuts, milk, egg, soy, wheat, fish and shellfish. Tree nuts include almond, hazelnut, walnut, pistachio, cashew, pecan, brazilnut, coconut and pine nut. Allergy to sesame seeds also seems to be prevalent. Federal law mandates that every food regulated by the FDA requires food labels that must include any of these 8 foods if they are part of the ingredients. This is why reading ingredient labels are so important for food allergic individuals.
How is food allergy diagnosed?
The ultimate “gold standard” for how food allergies are diagnosed is called a double-blind, placebo-controlled, food challenge. This is where the food in question is fed in increasing amounts to the patient, while alternating with a food that the patient can tolerate. Neither the patient nor the physician knows which dose is the food in question, hence the “double blinding”.
This procedure is both time consuming and labor intensive and is usually performed in a research setting. More practically, most physicians rely on both a prick skin test (PST) and a specific IgE antibody to standardized foods. However, the major limitations to these tests are that you can have a negative test and still be allergic or you can have a positive test and not be allergic, so they should be taken in context with the clinical history. Moreover, neither the size of the skin test nor the level of serum specific IgE can predict the severity of reaction. So someone with a small positive skin test or low specific IgE can still have anaphylaxis.
More recently, component food testing has become available to peanut, milk and egg. This involves serum IgE testing to certain component proteins of the food in question. It has been shown that different components of food may predict severity of reaction or tolerance to baked forms of the food. For instance, if patients are only sensitized to the component Arah8 in peanut, prognosis of tolerance is excellent. Patients highly sensitized to the casein component in milk tend to have persistent allergy and can not tolerate baked milk products. Sensitization to the ovomucoid component in egg indicates a likely intolerance to baked egg products.
What is oral allergy syndrome?
Oral allergy syndrome is not a true food allergy, but rather a syndrome caused by cross-reactivity of proteins between certain pollens and food allergens.
For example, patients who are ragweed allergic, may experience oral symptoms with ingestion of banana, cantaloupe, honeydew, watermelon, zucchini and artichoke. Patients who are birch pollen allergic may experience symptoms to apples, pears, carrots, apricots, peaches, cherries and kiwi.
Symptoms are typically mild and involve itching and/or tingling of the lips, mouth, tongue and throat, which usually do not progress to more serious reactions.
What can be done to treat food allergies?
Unfortunately, right now, food avoidance is the mainstay of “treatment” of food allergies. There is no cure for food allergies, although food allergies, like environmental allergies can change. Many children can outgrow their food allergies as they get older. Even 15-20% of children with peanut allergies will outgrow them. More rarely, adults without previous food allergy can develop them for unknown reasons. Most of these cases involve peanut or shellfish allergy.
There is also no evidence that early avoidance of certain foods will prevent food allergies. In the past, pediatricians and allergists recommended avoidance of milk, egg, nuts and fish until children were older, between the ages of 1 to 3. Now, with newer research, there has been a shift in this thinking.
Recently, there was a groundbreaking study showing that early introduction of peanut can prevent the development of peanut allergy. In the LEAP study (Learning About Peanut Allergy), 640 high-risk United Kingdom infants between the ages of 4 and 11 months were randomized to consume peanut products 3 times a week or completely avoid peanut products for the first 5 years of life. High risk was defined as patients with evidence of egg allergy or severe eczema. 542 patients had negative prick skin test (PST) and 98 patients had a minimally positive PST (1-4mm). 17.2% of patients in the peanut avoidance group and 3.2% of patients in the peanut consumption group ended up having a peanut allergy by age 5 years. This is a relative reduction of 80%. This study shows that early introduction of peanut is safe and effective.
The future of food allergy therapeutics
Much of the current research has been examining ways to induce tolerance and/or desensitize food allergic individuals. Immune tolerance is complete tolerance of the food regardless of consumption frequency. Desensitization requires regular consumption to maintain a non-allergic state. These methods include oral immunotherapy (OIT), sublingual immunotherapy (SLIT) and epicutaneous immunotherapy (EPIT). Oral immunotherapy involves gradually increasing oral amounts of allergenic foods. This involves an initial dose escalation, followed by gradual build-up and prolonged maintenance. The initial dose escalation occurs on a single day. The build-up phase involves increasing the dose every 1 or 2 weeks with daily home doses. Several trials have shown that OIT to peanut, egg and milk can induce desensitization in 50-93% of patients studied, allowing for significant amounts of peanut, egg and milk consumption. Complete immune tolerance has been more difficult to achieve.
SLIT immunotherapy is delivered subligually, so the food is in a liquid form and held under the tongue for 2 minutes. This is different than OIT in that the food is absorbed in its intact form rather than via gastric digestion. SLIT therapy is also daily for several months. SLIT has been shown to achieve significant desensitization to both peanut and milk in several trials. However, in direct comparison studies, OIT appears to be more effective than SLIT.
EPIT is a newer method that involves delivery of the food protein through the skin. This is done in the form of a patch that is attached and left on the patient’s skin for a period of time. Currently trials are under way for peanut and milk EPIT.
So although the future of food allergy seems bright, what will always remain of primary importance will be the diagnosis of food allergy and the recognition of symptoms of an allergic reaction. Only once a diagnosis has been made can adequate measures be taken to prevent, and prepare for, an adverse reaction.