People who are allergic to this carbohydrate can develop a anaphylactic reaction or hives

Meat from mammals like beef or pork contains a carbohydrate (a form of sugar) that is called alpha-gal. In a previous study, it was demonstrated that people who are allergic to this carbohydrate can develop a anaphylactic reaction or hives three to six hours after ingesting meat. Most food allergies cause symptoms much more early, which led to the general rule that if allergy symptoms occur later than one hour after eating, it can’t be the food. For certain meat allergies this does not seem to be true. However, the long time that it can take before symptoms show up after eating meat can make it very hard to recognize the true culprit. Researchers think that this has lead to an underestimation of the frequency of this type of meat allergy in the general population.

A study by Scott Commins, M.D., Ph.D. and his colleagues that was presented at the yearly meeting of the American Academy of Allergy, Asthma & Immunology (AAAAI) in February 2010, was designed to look into this question. Dr. Commins and colleagues studied sixty patients that suffered from recurrent, idiopathic anaphylaxis, which means the patients had anaphylactic reactions repeatedly, without a known cause. The researchers looked at a broad panel of possible substances these people might be allergic to. In twenty five out of the sixty patients (more than 40%), high levels of an antibody type called IgE was found that strongly reacted with alpha-gal. Antibodies are proteins that the immune system produces to fight bacteria and other intruders. High amounts of the IgE-type of antibodies that react with otherwise harmless substances are the cause of many allergic reactions, and most allergy tests look for IgE-type antibodies against many different substances people are frequently allergic too.

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Cause of an allergy symptoms remains a mystery

Examination of a large panel of other allergens did not show any results that would have explained the anaphylactic symptoms in these patients. However, no pattern that could explain the symptoms was found in the 35 patient that did not show the IgE antibody that reacted with alpha-gal, which means the cause of their allergy symptoms remains a mystery.

The results of the study are unusual in several aspects: they clearly show that allergies to a carbohydrate that is found in all mammalian meats are much more common than previously thought in people who suffer from anaphylaxis without a known cause. Further studies will need to be done to examine how common allergies to this substance are in people who suffer from allergy symptoms without a known cause and whose symptoms are less severe than in the case of these sixty patient who suffered from recurrent anaphylaxis.

The other reason why this study is unusual is that in most food allergies the offending substance, the allergen, is a protein, like e.g. in many allergies that are caused by tree nuts and peanuts. In these cases allergy symptoms are often more severe when the food that causes the allergies is eaten raw, as cooking can alter the proteins in a way that makes them unrecognizable for the IgE antibody. Some people e.g. are allergic to raw strawberries, but have no problems with strawberry jam or pie. In the case of the meat allergy, the allergy is caused by alpha-gal which is a carbohydrate (a form of sugar). To this date not many allergies caused by carbohydrates are known, but this study shows that allergies against carbohydrates might be much more common that formerly thought.

This possibility should be taken into account when examining patients who have allergy symptoms with unknown causes that show now clear reactivity with the usual allergen panels. There might be still many other underappreciated carbohydrate allergens out there. In contrast to protein allergens, that sometimes might be destroyed, or at least reduced by food preparation like boiling and broiling, carbohydrate allergens cannot be destroyed by heat.