It’s hard to believe that the very thing that is meant to provide us with sustenance and energy can have grave consequences on our health. Food allergies are not particularly common but they can be serious, and parents should know the difference between food allergies and food intolerances.
A food allergy is defined as an unusual reaction to certain foods that is triggered by a particular reaction in the immune system and the allergy is characterised by various symptoms. Intolerance to foods is also an unusual or abnormal reaction to the food and in many cases the symptoms are very similar to that of a food allergy, however, food intolerances are a lot more common and the intolerance is triggered by different mechanisms in the immune system. Those who have allergies to food need to identify the allergies and prevent them, as even though the reactions are usually not severe, in some cases allergies can result in illness and in very rare cases, allergies can be lethal.
What causes food allergies?
Our immune systems are designed to offer protection from infections. In order to provide this protection, the immune system produces types of proteins – which we know as antibodies. These antibodies are able to detect germs that cause infection. Several types of antibodies exist and the specific one that causes an allergic reaction is called IgE. It is believed that these antibodies are usually produced to respond to infections that are caused by parasites, like malaria. Some people, however, produce IgE as a reaction to things such as pollen and this causes them to suffer from hay fever, in some cases the IgE that is produced causes food allergies.
With a food allergy, the IgE attaches itself to molecules in the food, and as such, if a child or an adult has an allergy to a certain food, the IgE attaches itself to the molecules of the ingested ‘bad’ food and results in an allergic reaction. A common symptom that is triggered by the IgE antibody in response to an allergen is the release of histamine and this causes the common allergic symptoms that are experienced, such as wheezing, itching, swelling, etc.
Allergens are typically proteins and usually several different types of allergens are found in food. It is still a mystery as to why some foods cause allergies and others don’t, but a plausible theory is that some of the proteins which are present in foods closely resemble the proteins that are found in viruses or in bacteria.
Inheriting food allergies
As parents, we want to leave a legacy for our children – we certainly don’t want to leave them a food allergy. However, evidence exists to support the theory that food allergies are hereditary. Children who tend to have a lot of allergies, usually come from families where allergies are common. These may not necessarily be food allergies. A child who has two allergic parents is considered to be a ‘good’ candidate for developing an allergy to food than a child who only has one allergic parent.
There are several groups of foods which are responsible for causing allergies. The list below shows the most common allergenic foods.
Almost half of all infants will suffer from a cow’s milk allergy – an allergy to cow’s milk is the most common childhood food allergy. The good news is that children outgrow the sensitivity to cow’s milk and by the age of three, as many as 90% of children are no longer allergic to cow’s milk. It is rare for an adult to suffer from this allergy (remember that an allergy to cow’s milk is different to an intolerance to cow’s milk or lactose).
Common symptoms of this allergy are frequent bouts of vomiting and diarrhoea, and skin rashes are not uncommon. Few children have an anaphylactic reaction to milk and this appears to be a lifelong condition. The key allergens in milk are the caseins and the whey protein b-lactoglobulin. The proteins that are found in the cow’s milk are very similar to those in goats and sheep milk and as such the same reaction can be experienced by those who allergic to cow’s milk. This means that the milk of goats and sheep should not be used as a substitute for cow’s milk.
Shellfish allergies are rare in children and generally only affect adults. However, allergic reactions to fish are common in both children and in adults. A seafood allergy is more common in countries or regions where there is a high consumption of fish and shellfish. The major allergens in fish like cod are proteins known as parvalbumins. Shellfish allergens are typically found in the fleshy parts but can also be detected in the shells. Pregnant moms are often warned against eating shellfish or seafood during pregnancy, as it is believed that consuming these foods may result in the baby developing an allergy to fish and shellfish (however, this theory is not confirmed).
An allergy to eggs is common in young children and as with the allergy to cow’s milk it fades with age. In some cases, children who suffer from a severe form of allergy do not outgrow the allergy to eggs. The main allergens are the egg white proteins, ovomucoid, ovalbumin, and ovotransferrin.
Allergic reactions to fruits and vegetables are relatively mild and are often limited to the mouth. The allergens in fruits and vegetables are not as complex as other foods and most are similar to the allergens in pollens, which is why people who suffer with pollen allergies, have allergies to certain fruits. Most fruit allergens are eradicated by cooking and this means that cooked fruits are generally safe for those with allergies to fruit.
Tree nuts include pecan, hazelnuts, Brazil nuts, and walnuts. Although no extensive research has been done, it has been discovered that tree nuts can cause symptoms that are very severe and on occasion, fatal. Children who develop an allergy to tree nuts normally remain allergic for the rest of their lives. With nut allergens, the allergens can either be destroyed or become resistant when cooked and new evidence suggests that roasting nuts may actually create new allergens.
Peanuts are one of most allergenic foods and can cause intense reactions, including anaphylaxis. An allergy to peanuts is established in childhood and usually the child will remain allergic to peanuts throughout their lives. Both soya beans and peanuts have multiple allergens and the allergens are found in the raw and cooked foods. A peanut allergy can be serious enough that even small traces of peanut can cause a severe reaction. Traces of nuts found in processed oils or the residue of peanuts present on utensils may be enough to cause a severe reaction in some individuals. The major allergens in peanuts and soya beans are the proteins used by the seed as a food store for it to grow into a seedling. One of the allergens that are found in soya beans is very similar to the major allergen from dust mites.
Both children and adults may suffer from wheat allergy and this allergy appears to be associated with exercise-induced anaphylaxis. Cereals include barley, oats, wheat, rye, maize or rice and it has been found that the more cereals are consumed, the higher the likelihood is of developing an allergy to cereals. Seed storage proteins along with other proteins present in grain to protect it from attack by moulds and bacteria have been found to be one of the major allergens.