From hives to shock
All about food allergies
For someone with a food allergy, the average meal is akin to an obstacle course, where great care must be taken to avoid a particular ingredient. Consuming even a tiny amount of a food to which the body is allergic can result in marked physical discomfort, says Prof. Anura Weerasinghe, consultant physician and leading immunologist warning that severe allergic reactions can even be fatal.
As cases of people with food allergies and food intolerance are on the rise all over the world, Mediscene speaks with Prof. Weerasinghe about how best to identify and deal with the condition.
The physiology of food allergies
A food allergy occurs when the immune system reacts adversely to a specific protein found in that food. "Usually the immune system is there to protect us from the challenges to the body," reveals Prof. Weerasinghe, explaining that such challenges may come both from outside the body, as in the case of microbes, or from within the body, as in the case of cancer cells. In the case of a food allergy, your immune system may mistakenly identify a certain food, or component of food as a threat.
Reacting to the perceived threat, your system triggers the release of antibodies, namely immunoglobulin E (IgE) from plasma cells to combat the culprit food or food component (the allergen). The IgE gets bound to the surface of another cell (eg. mast cell). The next time you eat even the smallest amount of that food, explains Prof. Weerasinghe, the IgE antibodies sense it and signal the mast cells to release histamine and other chemicals into your bloodstream.
These chemicals cause a range of allergic signs and symptoms. "Histamine, in particular, is responsible for most of the signs and symptoms of allergy," reveals Prof. Weerasinghe, including most allergic responses ranging from hives to anaphylactic shock. "Under such circumstances, this immune response is harmful, leading to what is known as hypersensitivity," he adds.
Who gets food allergies?
Though you can develop a food allergy at any point in time, children are far more likely to develop, and ultimately grow out of, a food allergy. "About 6% of the child population in the West have food allergies," says Prof. Weerasinghe, "and the incidence declines as they grow older, so that only about 2% of adults will develop a food allergy." While statistics are not available for Sri Lanka, Prof. Weerasinghe says that the number of people with allergies is only increasing. Genes have some say in the matter as well, and a vulnerability to allergies often runs in families.
Food allergens: - the part of the food that actually causes the allergic reaction - are usually proteins, reveals Prof. Weerasinghe. Some commons allergens are peanuts, shellfish such as shrimp, lobster and crab, as well as tree nuts such as walnuts. Interestingly, some 'heaty' fish like kelawalla have histamine already and can trigger allergies. In children, food allergies are also commonly triggered by proteins in foods like cow's milk, wheat and soybean products.
Common signs and
Food allergies can be very uncomfortable things. Amongst the most common symptoms are hives, swelling of throat, itching all over the body, diarrhoea, vomiting and abdominal pain, runny nose, swelling of lips, and difficulty in breathing due to broncho-constriction. In acute cases, a patient may even abruptly go into anaphylactic shock, which can be fatal and is marked by leakage of fluid from the bloodstream into the tissues and a drop in blood pressure.
"The first thing in the management is proper diagnosis," states Prof. Weerasinghe, emphasising the need to identify the offending allergen. In some cases more than one allergen may be to blame. Key to identifying the culprits is taking the time to do a thorough history of the individual. This is made easier by that fact that the signs and symptoms of an allergy are usually manifested within a few hours, says Prof. Weerasinghe, explaining that this makes it all the easier to remember.
Often a physician will ask a patient to keep a food diary, which is especially helpful in cases where it is not say a dish but a specific ingredient that is triggering the allergy. Your physician may also ask you to take an IgE estimation, or a skin prick test in which you are exposed to several allergens, while doctors watch for a specific reaction.
However, more often than not, the best judge is the person. "The patient will come and say look doctor, I get this only after eating this," relates Prof. Weerasinghe.
Could it be food intolerance?
"It is very important to know that there are certain diseases that mimic allergy such as food intolerance - caused by adverse reactions to a food ingredient like monosodium glutamate - and food poisoning," reveals Prof. Weerasinghe. In fact, a majority of individuals will suffer from some type of food intolerance rather than a food allergy, he reveals.
Food intolerance is different from a food allergy because it does not have an immunological basis and neither will it lead to anaphylactic shock.
Food intolerance commonly occurs when the body does not produce enough of a particular chemical or enzyme that's needed for the digestion of a specific food. For example, one of the most common manifestations of intolerance in Asians is of dairy products, and specifically of lactose. Some people have a shortage of the enzyme lactase, which is normally made by cells lining the small intestine, reveals Prof. Weerasinghe. Without this enzyme they can't break down milk sugar into simpler forms that can be absorbed into the bloodstream. Lactose intolerance, which can be brought on by enteritis can also cause symptoms very similar to irritable bowel syndrome. Once again, avoidance of that particular food is the simplest form of prevention. When symptoms persist over a period of time, it is always advisable to undergo a thorough check-up to rule out other possible illnesses like cancer, or even worm infestation, that may have led a patient to acquire a food allergy.
The first step in treatment is also the most obvious. Once you've identified the allergen, avoid consuming it - at least for awhile. Remember that allergies often vanish given time, and so this is not for life. However, prevention is not always possible. During an acute attack, one should immediately take an anti-histamine like chlophenaramine (eg. Piriton), recommends Prof. Weerasinghe. But be aware, he cautions, that medicines like Piriton have a sedative action; and so one must avoid it if involved in an activity, like driving, that requires alertness. In such cases, non-sedative anti-histamines (e.g Citrazine) are available.
An acute attack will necessitate a visit to the hospital, where someone with anaphylactic shock may be given a shot of life-saving adrenaline. However, if you are planning to go on a trip where a hospital is not easily accessible, it is always advisable to carry a self-injectable form of adrenaline, says Prof. Weerasinghe. Though not available in Sri Lanka, these pen type injections can be imported and are often worth the trouble, he reveals. Keep everyone informed. If you are eating out and are allergic to something, make it a point to let the management or your hosts know. Be careful that cooking utensils and cutlery are never confused. If you are going out alone, Prof. Weerasinghe suggest that one carry a tag, or some card that will inform anyone who needs to help you what you are allergic to. In the case of children, always inform the school.
Be aware that food allergies can be precipitated by exercise and alcohol. In such cases, refrain from exercising or drinking for a few hours after or before eating.
Interestingly, recovering from a food allergy may have a lot to do with your mind. Prof. Weerasinghe explains that intense anxiety about consuming a food after a previous attack may actually prevent you from getting over a certain allergen. So remember, the more relaxed you are, the more likely it is that you will be pleasantly surprised when you next reach for some delicious shrimp.