Why are some people allergic to certain foods?

Angela Uwamahoro has a 12-month-old baby. While introducing him to solid food she noticed that he could not tolerate cow milk. The baby vomited and became pale whenever he tasted milk. After realising this trend, Uwamahoro suspended cow milk, but she wonders what could be behind that condition. The condition is none other than food allergy. According to medics, all allergic reactions are a result of the body’s defense mechanism against foreign intruders it (mistakenly) perceives as harmful. In that case the immune system responds to the threat by pumping out antibodies, which in turn triggers the release of protective chemicals. Dr Edgar Kalimba , a pediatrician at King Faisal Hospital, Kigali, says though any food can cause such an allergic response, some are notorious for provoking the immune system, while others are almost universally harmless. While any food can cause an adverse reaction, eight types of food account for about 90 per cent of all reactions. These include eggs, milk, peanuts, tree nuts, fish, wheat and soy. Symptoms Kalimba says symptoms of a food allergy can range from mild to severe. Just because an initial reaction causes few problems doesn’t mean that all reactions will be similar; a food that triggered only mild symptoms on one occasion may cause more severe symptoms at another time. “The most severe allergic reaction is anaphylaxis, a life-threatening whole-body allergic reaction that can impair your breathing, cause a dramatic drop in your blood pressure and affect your heart rate. Anaphylaxis can come within minutes of exposure to the trigger food. It can be fatal and must be treated promptly with an injection of epinephrine (adrenaline),” he explains. Kalimba adds that children may outgrow their allergic reactions to milk and eggs. Peanut and tree nut allergies are likely to persist. Symptoms of an allergic reaction may involve the skin, the gastrointestinal tract, the cardiovascular system and the respiratory tract, he says. The medic explains that allergies can surface in one or more of the following ways: Vomiting and/or stomach cramps, shortness of breath, wheezing, repetitive cough, shock or circulatory collapse, tight, hoarse throat, trouble swallowing and swelling of the tongue, among others. “Most food-related symptoms occur within two hours of ingestion; often they start within minutes. In some very rare cases, the reaction may be delayed by four to six hours or even longer. Delayed reactions are most typically seen in children who develop eczema as a symptom of food allergy and in people with a rare allergy to red meat caused by the bite of a lone star tick,” he says. However, Dieudonne Bukaba, a nutrition expert, says not everyone who experiences symptoms after eating certain foods has a food allergy or needs to avoid that food entirely; for instance, some people experience an itchy mouth and throat after eating a raw vegetable. “This may indicate oral allergy syndrome - a reaction to pollen, not to the food itself. The immune system recognizes the pollen and similar proteins in the food and directs an allergic response to it. The allergen is destroyed by heating the food, which can then be consumed with no problem,” he says. Diagnosing food allergies Bukaba says a food allergy will usually cause some sort of reaction every time the trigger food is eaten. Symptoms can vary from person to person, and one may not always experience the same symptoms during every reaction. To make a diagnosis, the medics ask detailed questions about your medical history and your symptoms. Be prepared to answer questions about: What and how much you ate, how long it took for symptoms to develop, what symptoms you experienced and how long they lasted. “After taking your history, skin tests and/or blood tests can be taken which indicate whether food-specific immunoglobulin E (IgE) antibodies are present in your body. A liquid containing a tiny amount of the food allergen is placed on the skin of your arm or back. “Blood tests, which are a bit less exact than skin tests, measure the amount of IgE antibody to the specific food(s) being tested. The results of these tests are used in making a diagnosis. Once a food allergy is diagnosed, the most effective treatment is to avoid the food but also a patient may get prescribed medicines to alleviate the symptoms,” Bukaba explains. He adds that in some cases, an oral food challenge is taken. This test is helpful when the patient history is unclear or if the skin or blood tests are inconclusive. It also can be used to determine if an allergy has been outgrown. “During an oral food challenge, which is conducted under strict medical supervision, the patient is fed tiny amounts of the suspected trigger food in increasing doses over a period of time, followed by a few hours of observation to see if a reaction occurs,” Bukaba says. Management and treatment Claudette Kayitesi, a nutritionist at University Teaching Hospital of Kigali, says the primary way to manage a food allergy is to avoid consuming the food that causes you problems. “Carefully check ingredient labels of food products, and learn whether what you need to avoid is known by other names. Other medications may be prescribed to treat symptoms of a food allergy.” Can you outgrow food allergies? Kayitesi says children generally, but not always, outgrow allergies to milk, egg, soy and wheat. If a food allergy develops as an adult, chances are much lower you will outgrow it. Food allergies in adults tend to be life long, though there has not been a lot of research in this area. Prevention Medics say the only way to prevent a food allergy reaction is to avoid the food and any items that contain it as an ingredient. Ongoing studies indicate it may be possible to “desensitise” children, even those with severe reactions. However, exclusive breast-feeding for at least six months decreases the incidence of atopic dermatitis, cow’s milk allergy and wheezing in early life.

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Why are some people allergic to certain foods?