Food Allergies & Allergic Reactions

Today, over 12 million Americans have a food allergy. Over 6 million are allergic to seafood (which can cause an iodine deficiency). Food allergies are responsible for more than 30,000 emergency room visits each year. Approximately 3-4% of the adult population, and 6-8% of children, have food allergies. The number of children with peanut allergies has doubled over the past 5-year period.

What is a food allergy?

There are times when your immune system decides that a particular food is harmful, decides to attack it, and creates specific immunoglobulin E (IgE) antibodies to fight it. The next time you eat that food, the IgE antibodies sense it and signal the immune system to release massive amounts of chemicals (called "mediators") and histamines. The histamines cause swelling and redness, and can close vital airways. This is known as a food allergy.

Your symptoms may include:

Symptoms typically appear within minutes to two hours after you have eaten the food to which you are allergic. A severe allergic reaction is called anaphylaxis, which is characterised by closing of the airways.

Any food has the potential to cause a reaction, but eight foods are responsible for up to 90% of all food allergy reactions.

These are:

Children generally are allergic to eggs, milk, peanuts, and tree nuts. Adult allergies includes fish, shellfish, tree nuts, and peanuts. People can also be allergic to fruits and vegetables. Rather than the foods themselves, they have an allergy to fruit and vegetable pollens and/or proteins.

A food allergy is NOT the same as food intolerance. Intolerance to food does not involve the immune system.

What am I allergic to?

Food allergy tests help identify or exclude specific foods as a cause of your symptoms. Your doctor will decide what tests to perform and how to interpret the results. There are several different tests your doctor can perform:

The Elimination Diet

Your doctor may put you on the elimination diet. You replace foods that you think you might have an allergy to with other foods that provide the same nutrients as those you've eliminated.

Two to three weeks later, your physician will have you gradually reintroduce the foods you eliminated. If your symptoms return, it is probable that that particular food is responsible for your food allergy. If you again eliminate the foods that caused your symptoms and they clear up, most likely you are allergic to that food.

It is not a foolproof method and should be followed by more sophisticated testing.

Skin Prick Test

Your physician can determine what you are allergic to by doing a skin prick test. Drops of suspected substances are placed on your forearm or back. The skin is pricked by a needle, allowing a tiny amount of the substance to enter the skin. If you are allergic to the substance, a small bump will form at the site within 15 minutes.

Radioallergosorbent Test (RAST)

Your doctor might decide on a radioallergosorbent test (RAST). You will have to give a blood sample. A medical laboratory tests it with specific foods to determine if IgE antibodies are present. You will get the results back in about a week. A RAST is often used for young children or patients with skin problems that make it difficult to accurately read the results of a prick skin test. The results of either test are combined with your medical history to determine whether a food allergy exists.
Both tests are reliable.

How careful must I be about the foods I buy?

If you know or suspect that you are allergic to something, you must check the ingredient labels for every food you intend to buy. If a product doesn't have a label, you should avoid that food. Likewise, if a label contains unfamiliar terms, ask for a clarification or avoid eating that food.

An ounce of prevention is worth a pound of cure: Stay away from allergy-causing foods.

What should I do if I have an allergic reaction to food?

In most cases, you will need a shot of epinephrine. This is available by prescription in injectable form, such as EpiPen® or Twinject®. You should always have your prescribed medication, such as antihistamines or epinephrine, available.

What research is being undertaken to better understand food allergies?

Although there is no cure for food allergies, research is promising. Children can outgrow their food allergies, while adults don’t. In both cases, peanuts, nuts, fish, and shellfish are usually lifelong allergies. Physicians have learned that a decrease in sIgE levels over time helps patients develop greater tolerance to milk and egg allergies.

Researchers found that roasted peanut protein inhibited digestive enzymes. Another study looked at combining activated charcoal with peanut protein to prevent or stop absorption in the stomach after accidental ingestion. Scientists have found that the allergy to peanuts may have an environmental component.

Washing hands and tabletops with liquid soap, bar soap, or commercial wipes removes the major peanut allergen, Ara h 1. Plain water and antibacterial hand sanitizer, however, left detectable amounts of Ara h 1. Common household cleaning agents, except dishwashing liquid, removed peanut allergen from table tops.

 

References

American Academy of Allergy, Asthma &Immunology
Burks, Wesley. (2002). Food Allergies: Epidemiology. Medscape Today
Maleki SJ. et al. (2003). The major peanut allergen, Ara h 2, functions as a trypsin inhibitor, and roasting enhances this function. Journal of Allergy and Clinical Immunology
Perry, T.T et al. (2004). Distribution of Peanut Allergen in the Environment. Journal of Allergy and Clinical Immunology
Shek, L.P. et al. (2004). Determination of Food Specific Ige Levels Over Time can Predict the Development of Tolerance in Cow's Milk and Hen's Egg Allergy
Sicherer, S.H. et al. (2004). Prevalence of Seafood Allergy in the United States Determined by a Random Telephone Survey. American Academy of Allergy, Asthma &Immunology
The Food Allergy & Anaphylaxis Network
Vadas, P. (2003) Activated charcoal forms non-IgE binding complexes with peanut proteins. Journal of Allergy and Clinical Immunology

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