Food Allergy (hypersensitivity) is an adverse immune response to a food protein. It caused by an immunoglobulin E (IgE) mediated reaction that occurs when the immune system reacts to a normally harmless food protein that the body mistakenly identified as harmful (Mahan & Stump, 2004). The reaction occurs consistently after ingestion, inhalation of touch of a particular food causing functional changes in target organs. IgE reactions usually occur instantly or within 2 hours of exposure, with severity ranging from mild to life threatening.
Basically, all foods containing protein can cause allergy. However, only 8 foods contribute to 90% food allergy. Those allergens* are:
– Tree nuts
Symptoms & Diagnostic Tests
Food allergies have wide range of symptoms. The details are as follows:
|Gastrointestinal||Abdominal pain, nausea, vomiting, diarrhea, GI bleeding, protein-losing enteropathy, oral & pharyngeal pruritus|
|Cutaneous||Urticaria, angioedema, eczema, erythema, itching,flushing|
|Respiratory||Rhinitis, Asthma, Cough, Laryngeal edema, Heiner’s syndrome, Airway tightening|
|Systemic||Anaphylaxis, Hypotension, Dysrhythmias|
|Controversial/Unproven||Behavioral disorders, tension fatigue syndrome, ADHD, Otitis media, psychiatric disorders, neurologic disorders, musculoskeletal disorders, migraine headache|
Amongst all allergic reactions, systemic anaphylaxis is the most dangerous one, can include abdominal pain, nausea, vomiting, cyanosis, blood pressure drop, angioedema, chest pain, urticaria, diarrhea, shock & death. Although anyone who has food allergy can experience it, the most likely foods to cause anaphylaxis are peanuts, tree nuts, fish & shellfish.
No simple test can be used to diagnose food allergy, because it requires suspected food identification, proof that the food causes an adverse response & immunologic involvement verification. Below are some proven tests that can be used for diagnosing food allergies:
Type of Test
|Skin testing(scratch, prick or puncture)||A drop of antigen is placed on the skin & the skin is then scratched or punctured to allow penetration||Screening tests; the most economic & provide results within 15-30 minutes; must be followed by DBPCFC*|
|Radioallergosorbent test (RAST)||Serum is mixed with food on a paper disk then washed with radioactively labeled IgE||Blood test; no more accurate than skin test but more costly; might useful for people with skin disease|
|Enzyme-linked immunosorbent assay (ELISA)||Like RAST, except no radioactive material is used||Same as for RAST|
|CAP, RAST fluoroscein-enzyme immunoassay (FEIA)||Compared to RASt, this test binds more allergen||Promising test but reliable for only 6 foods (egg, milk, peanut, fish, wheat & soy)|
|Specific IgG, IgM, IgA antibody assays||Requires special expertise for techniques (precipitation hemagglutination, complement fixation)||Blood test, Best used in research only|
To help diagnose a food allergy, the allergist doctor might ask the patient to temporarily eliminate specific foods. This method, combined with skin or blood test can be helpful in diagnosing both IgE-mediated food allergy & related disorders. Generally, food elimination diet will last 2-4 weeks. If the elimination diet is inconclusive, the allergist may recommend a food challenge to confirm the results
There are 3 kinds of food challenge: OFC (Open Food Challenge) which allows the food to be given openly, SBPCFC (Single Blind Food Challenge) in which the food is hidden from the patient with at least 1 placebo, and DBPCFC* (Double blind Placebo Controlled Food Challenge), in which food is hidden from the patient & presented with at least 1-3 placebos. DBPCFC is considered the “gold standard” for diagnosing food allergy.
How to deal with it?
Total avoidance of food allergens is the only proven treatment for food allergy. An effective food allergy treatment plan includes all of the following:
– Strict avoidance of problem foods
– Develop Emergency Care Plans with the doctor
– Wearing emergency medical identification (ex: bracelet) at all times
– Carrying medication wherever going (ex: steroids, antihistamine, asthma medicaton & epinephrine for patient with anaphylaxis risk)
– Taking medication at the first sign of a reaction
– Getting to an emergency room for follow-up treatment if facing severe reaction
Food immunotherapy vaccine is a possible future treatment meant to complement food allergen avoidance. The vaccine’s purpose will be to prevent allergic reaction, or reduce the severity& prevent death in accidental exposure. However, it still considered experimental.
What’s the difference between food allergy & food intolerance?
While food allergy is an adverse food reaction caused by IgE immunologic mechanism, food intolerance is an adverse food reaction caused by non-IgE mechanisms, including toxic, pharmacologic, metabolic or idiosyncratic reaction. The symptoms of food intolerance are often similar to food allergy, but the treatment may be different depending on the mechanism involved. For example: lactose intolerance & milk allergic. Lactose intolerance is food intolerance, while milk allergic is food allergic. Lactose intolerance is caused by enzyme lactase deficiency while milk allergic caused by IgE reaction to milk protein. The symptoms of both are similar such as abdominal cramping, flatulence & diarrhea after ingestion, but the diagnosis & treatment should be different. Skin or blood testing cannot be used to detect food intolerance. Many food intolerances may allow ingestion of the offending foods, while food allergies have to totally avoid those.
Mahan, K. & Stump, S.E. 2004. Krause’s Food, Nutrition & Diet Therapy. 11th Edition. USA: Elsevier.