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Know Your Food Allergy

Posted Apr 18 2009 12:00am

It’s critical for people who have food allergies to identify them and to avoid foods that cause allergic reactions. The word ‘allergy’ means that the immune system has responded to a harmless substance as if it were toxic. Allergies are an over-reaction of the body’s immune system to a specific component, usually a protein. These proteins may be from foods, pollens, house dust, animal hair or mounds and are known as allergens.

What is Food Allergy

A food allergy is an abnormal response to a food triggered by the immune system. Food normally doesn’t provoke a response from the human immune system, the body’s defense against microbes and other threats to health. In food allergies, two parts of the immune response are involved,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 occur in all body tissues but especially in areas that are typical sites of allergic reactions, including the nose, throat, lungs, skin, and gastrointestinal tract.

Our bodies are protected from infections by our immune system. We produce molecules, called antibodies, which recognise the germs causing an infection. There are a number of different sorts of antibody, and the one which causes an allergic reaction is called immunoglobulin E (IgE).

The IgE acts like a tag, sticking to molecules in food or pollen called allergens. When someone who has an allergy eats a problem food the IgE attaches to the allergens, setting off an allergic reaction. One of the common effects that IgE triggers is the release of histamine, which causes the changes we see in our bodies as symptoms, like nettle rash or wheezing.

Allergens are usually proteins, and there are generally several kinds of allergen in each food. We do not know what makes some proteins, and not others, food allergens

Risk  of Food Allergy May increase if:

  • You have a family history of allergy. Food allergies are most common in people who are atopic, meaning they have an inherited tendency to develop allergic conditions such as asthma, various allergies, and atopic dermatitis. If both of your parents have allergies, you have an increased chance of developing allergies.
  • You have another allergic condition such as atopic dermatitis or asthma.
  • You are young, Infants and children have more food allergies than adults.
  • You have a medical condition that makes it easier for allergens to pass through the walls of the stomach and intestines and enter the bloodstream. These conditions include gastrointestinal disease, malnutrition, prematurity, and diseases that impair the immune system.

Symptoms of food allergy

The onset of symptoms from food allergy tend to be more immediate and can be life-threatening. Common symptoms include:

  • Itching and burning and swelling around the mouth
  • Runny nose
  • Skin rash and hives, eczema, urticaria (skin becomes red and raised)
  • Diarrhoea, abdominal cramps
  • Breathing difficulties, including wheezing and asthma
  • Vomiting, nausea
  • Life-threatening anaphylaxis.

Allergenic Foods Includes:

Cow’s Milk: Two out of a hundred infants under one year old suffer from cow’s milk allergy, making it the most common food allergy of childhood. In general children lose this sensitivity as they grow up with nine out of ten losing it by the age of three; it is unusual for adults to suffer from this allergy.  Symptoms are frequently vomiting and diarrhoea in children, with 30-50% also having skin rashes of some type. A small number of children have an anaphylactic reaction to milk which tends to be lifelong. The major allergens in milk are the caseins and the whey protein b -lactoglobulin. People are usually allergic to more than one kind of milk protein. The proteins from cow’s milk are very similar to those from goats and sheep, and can cause the same sorts of reaction in cow’s milk-allergic subjects. Thus goat’s or sheep’s milk cannot be used as a cow’s milk substitute in allergic individuals.

Eggs: Allergy to eggs is usually observed in young children rather than adults, and like cow’s milk allergy, fades with time. Occasionally children suffer from a severe form of allergy which is not outgrown.  The main allergens are the egg white proteins ovomucoid, ovalbumin, and ovotransferrin. The eggs of other poultry, such as ducks, are very similar to those of hens and can cause reactions in egg-allergic individuals.

Fish and shellfish: Allergies to shellfish are unusual in children, mostly being experienced by adults. Reactions to fish are found in children and adults. The incidence of seafood allergy is higher in those countries with a high consumption of fish and shellfish. Severe reactions are more frequently found with these foods, including anaphylaxis. Cooking does not destroy the allergens in fish and shellfish, and some individuals maybe allergic to the cooked, but not raw, fish. The major allergens in fish are flesh proteins called parvalbumins which are very similar in all kinds of fish. This is why people allergic to cod tend to be allergic to fish such as hake, carp, pike, and whiting as well. Shellfish allergens are usually found in the flesh and are part of the muscle protein system, whilst in foods such as shrimps, allergens have also been found in the shells.

Fruits: In general allergic reactions to fruits and vegetables are mild, and are often limited to the mouth, and are called the oral-allergy syndrome (OAS).  Around four out of ten people having OAS are also allergic to tree and weed pollens. Thus people who are allergic to birch pollen are much more likely to be allergic to apples.There allergens in fruits and vegetables are not as complicated as other foods. Many of them are very like the allergens in pollens, which is why people with pollen allergies are also allergic to certain fruits.
Many fruit allergens are destroyed by cooking, and thus cooked fruits are often safe for fruit allergic people to eat.  Allergies to latex gloves, especially amongst health professionals, are increasing. As many of the latex allergens are like those found in certain tropical fruits, such as bananas, these people can get an allergic reaction to handling or eating these foods .

Legumes: This group of foods includes soya beans and peanuts. Peanuts are one of most allergenic foods and frequently cause very severe reactions, including anaphylaxis.

Allergy to peanuts is established in childhood and usually maintained throughout life. Both these foods have multiple allergens which are present in the raw and cooked foods. Peanut allergy can be so severe that only very tiny amounts of peanut can cause a reaction. Thus the traces of nuts found in processed oils, or the carry over of materials on utensils used for serving foods, can be enough in some individuals, to cause a reaction. The main allergens in peanuts and soya are the proteins used by the seed as a food store for it to grow into a seedling. One of the allergens in soya bean is very similar to a major allergen from dust mites, a common environmental allergen. We aren’t sure yet whether this means there is a link between dust allergy and soya allergy.

Tree nuts: This group includes true tree nuts, such as Brazil nuts, hazelnuts, walnut and pecan.

Whilst not as intensively studied as peanuts, indications are that tree nuts can cause symptoms as severe which can occasionally be fatal. Children who become sensitised to tree nuts tend to remain allergic throughout life.
Hazelnut and almond allergies are more like those people get to fruit, and are linked to pollen allergies. Nut allergens can be both destroyed by, or resistant, to cooking and we think that roasting may actually create new allergens.The allergens can be the seed storage proteins, or other molecules which are also found in pollen.

Cereals: Suffered by children and adults alike, wheat allergy appears to be particularly associated with exercise-induced anaphylaxis. The more of a cereal (wheat, rye, barley, oats, maize or rice) we eat the more likely we are to suffer an allergy. Thus rice allergy is found more frequently in populations eating ethnic diets.     Seed storage proteins (such as wheat gluten) and other proteins present in grain to protect it from attack by moulds and bacteria, have been found to be major allergens.
How to Treat a Food Allergy

The best treatment is to never eat the foods you are allergic to. Learn to read food labels and spot other names for problem foods. For example, milk may be listed as “caseinate,” wheat as “gluten,” and peanuts as “hydrolyzed vegetable protein.” When you eat out or at other people’s houses, ask about the foods you are served.

If you do eat a food you are allergic to, medicines can help. You may be able to stop a mild reaction by taking over-the-counter antihistamines. You may need prescription medicines if over-the-counter drugs do not help or if they cause side effects, such as making you feel sleepy.

If you have severe food allergies, your doctor will prescribe an allergy kit that contains epinephrine (say “eh-puh-NEH-fren”) and antihistamines. An epinephrine shot can slow down or stop an allergic reaction.

In conclusion Food allergies are rare. Most reactions to food are a food intolerance. The symptoms usually affect three main sites of the body – the skin and the respiratory and digestive systems.

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