Sunday August 20, 2006
Common food allergens made simple
By DIONG SWEE HOON
ALLERGIES affect the lives of millions of people around the world. Fresh flowers, a friend’s cat or dog, even the presence of dust can make people itch, sneeze, and scratch almost uncontrollably. But what about that seemingly innocent peanut butter sandwich, glass of milk, or fish nuggets?
A food allergy, or hypersensitivity, is an abnormal response triggered by the body’s immune system to something in a food or an ingredient in a food – usually a protein. A true food allergy (also called “food hypersensitivity”) and its symptoms can take many forms.
While many people often have gas, bloating or other unpleasant reactions to something they eat, this is not an allergic response. Such a reaction is thought to not involve the immune system and is called “food intolerance”. A food allergy is an exaggerated immune response triggered by eggs, peanuts, milk, or some other specific food.
Food normally does not provoke a response from the human immune system, the body’s defence against microbes and other threats to health. In food allergies, two parts of the immune response are involved, according to researchers at the National Institute of Allergy and Infectious Diseases.
One is the production of an antibody called immunoglobulin E (IgE) that circulates in the blood. The other part is a type of cell called a mast cell. Mast cells are situated in all body tissues, but especially in areas that are typical sites of allergic reactions, including the nose, throat, lungs, skin, and gastrointestinal tract.
People usually inherit the ability to form IgE against food. Those more likely to develop food allergies come from families in which allergies such as hay fever, asthma, or eczema are common.
If the mast cells release chemicals in the nose and throat, the allergic person may experience an itching tongue or mouth and may have trouble breathing or swallowing. If mast cells in the gastrointestinal tract are involved, the person may have diarrhoea or abdominal pain. Skin mast cells can produce hives or intense itching.
The food protein fragments responsible for an allergic reaction are not broken down by cooking or by stomach acids or enzymes that digest food. These proteins can cross the gastrointestinal lining, travel through the bloodstream and cause allergic reactions throughout the body.
The timing and location of an allergic reaction to food is affected by digestion. For example, an allergic person may first experience a severe itching of the tongue or “tingling lips”. Vomiting, cramps or diarrhoea may follow.
Later, as allergens enter the bloodstream and travel throughout the body, they can cause a drop in blood pressure, hives or eczema, or asthma when they reach the lungs. The onset of these symptoms may vary from a few minutes to an hour or two after the food is eaten.
Which foods cause food allergy?
Although an individual could be allergic to any food, such as fruits, vegetables, and meats, there are eight most common food allergens that account for 90% of all food-allergic reactions. These are: milk, egg, peanut, tree nut (walnut, cashews, etc.), fish, shellfish, soy, and wheat.
What are the symptoms of food allergy?
Symptoms of food allergy differ greatly among individuals. They can also differ in the same person during different exposures. Allergic reactions to food can vary in severity, time of onset, and may be affected by when the food was eaten. Exercise can also be a factor too.
Some food allergies affect only the gastrointestinal tract (stomach and intestines). These are often infant or early childhood conditions, but some can persist. An example of a persistent allergy is celiac disease, which is an abnormal immune response to certain proteins in gluten, a type of protein found in wheat and barley. This condition is also diagnosed in adults – in fact, the most common age at diagnosis now is about 40, and most patients have had at least 10 years of symptoms before diagnosis.
Common symptoms of food allergy include skin irritations such as rashes, hives, and eczema, and gastrointestinal symptoms such as nausea, diarrhoea, and vomiting. Sneezing, runny nose, and shortness of breath can also result from food allergy, but such symptoms are usually seen at the same time as symptoms in other areas of the body in a more severe reaction.
In other words, isolated sneezing and runny nose, or isolated shortness of breath is not common with food allergy. Some individuals may experience a more severe reaction called anaphylaxis.
What is anaphylaxis?
According to the American Academy of Allergy, Asthma and Immunology (AAAAI), anaphylaxis is a life threatening allergic reaction.
It is a condition which affects several different parts of the body, which may include the skin: flushing, itching, or hives; the airway: swelling of the throat, difficulty talking or breathing; the intestines: nausea, vomiting, or diarrhoea; and the ability of the heart to pump blood: low blood pressure or unconsciousness.
Symptoms usually appear rapidly, sometimes within minutes of exposure to the allergen, and can be life-threatening. Immediate medical attention is necessary when anaphylaxis occurs. Standard emergency treatment often includes an injection of epinephrine (adrenaline) to open up the airway and help reverse the reaction.
The only proven treatment for a food allergy is to avoid the food! If you suspect you or your child has a food allergy, consult an allergy specialist.
Antihistamines [these work by blocking the action of histamine at special sites (receptors) in the skin, nose, blood vessels and airways] are the most common treatment for mild to moderate allergic reactions whilst injections of epinephrine (adrenaline) as mentioned are used for severe reactions such as anaphylaxis.
1. International Food Information Council Foundation (IFIC) – Understanding Food Allergy
2. Medline Plus Medical Encyclopedia – Food Allergy
3. BUPA UK
The allergy march is on