Food intolerance
Food allergy is different from food intolerance. The former involves the body’s immune system but the latter does not. Food allergic reactions occur with the smallest amount of the food item. Food intolerance is usually dose related, that is, small amounts of the food item are tolerated by the body but larger amounts lead to a reaction which may mimic food allergy. Food intolerance is of slower onset than food allergy and is not life-threatening.
Allergens
Any food can cause an allergic reaction. The common allergy-provoking food in children includes cow’s milk protein, egg, soya bean, wheat, peanuts and fish. The common allergy-provoking food in adults includes nuts, mushrooms and seafood such as fish, prawn, crab, shrimp, clam and squid.
Food allergies have also been attributed to certain food additives and preservatives but this is disputed by some experts. The additives and preservatives include monosodium glutamate (MSG), sodium benzoate, sulphites and tartrazine.
Some young adults may suffer from localised oral allergies. They have an itchy throat and mouth when they consume certain fresh fruits (such as apple or cherry), vegetables (carrot or celery) and nuts.
Consequences
The individual who has a food allergy may be affected in more ways than one. Although the clinical features are generally mild, an anaphylaxis may occur which can be life-threatening. The non-consumption of certain foods without a substitute food can result in nutritional deficiency with its attendant consequences, including poor growth in a child.
A food allergy usually occurs within minutes of consuming a small amount of the food item. The clinical features include itching, particularly around the mouth; swelling of the mouth and/or throat; generalised body rashes; wheezing; nausea; diarrhoea; vomiting and occasionally anaphylaxis.
Anaphylaxis is an extreme allergic reaction which may occur at any age but rarely in babies. It usually starts with the clinical features in the previous paragraph but progresses to breathing difficulties; marked swelling of the mouth and throat; rapid pulse rate; severe abdominal pain, vomiting and/or diarrhoea; weakness or dizziness due to a sudden drop in blood pressure; collapse and unconsciousness.
An anaphylaxis is life-threatening and usually occurs rapidly, although the clinical features may sometimes occur up to an hour or so after consumption of the food item.
Management
A consultation with the doctor is essential if a food allergy is suspected. The doctor will take a history which would include details about the reaction and whether there is a family history of other allergies (for instance allergic rhinitis, asthma or eczema) and conduct a physical examination. A referral to a specialist may be made by the doctor.
The keeping of a detailed diary of all foods consumed, together with the clinical features of any reaction, for about a fortnight prior to consulting the doctor would be helpful in the elucidation of the causative agent. The diary should contain details of all foods, drinks and medicines, including food supplements, consumed. The clinical features of any reaction, its intensity and timing in relation to the food consumed should be recorded. The food diary would be helpful in directing allergy tests.
Skin-prick testing involves placing drops of various diluted foods on the arm and then introducing the food drops into the body by pricking the skin with needle or lancet. A positive reaction is indicated itchiness, redness and swelling at the site of the prick. This test is safe. The accuracy of the test depends on whether the reaction is negative or positive. If the result is negative, the results are about 90% accurate but if it is positive, it is about 50% accurate.
Tests done on a blood sample to detect antibodies to specific foods provide information about the likelihood of an allergy to the foods. Negative results are about 90% accurate, but positive results are about 50% accurate.
The gold standard in food-allergy testing is challenge-testing, which involves the consumption of a small amount of the suspected food item under the supervision of a specialist in a hospital. The reason for this precaution is because of the likelihood of an anaphylaxis. A diagnosis can be made if a reaction is observed. Challenge-testing is time-consuming, costly and cannot be done on those with asthma or other allergic reactions.
A positive diagnosis of food allergy can only be made by taking into consideration the history, physical examination and the results of tests. If the identification of the food item is not possible but food allergy is suspected, an elimination diet will be suggested. This involves non-consumption of certain food items and gradual reintroduction into the diet. A food diary is kept with a record of any clinical features of an allergic reaction. The test is usually done under the dietician’s supervision in order to avoid any nutritional deficiency.
Although there is no cure for food allergy, it can be managed by avoiding the causative food item. The diet consumed has to be planned to ensure that it is nutritionally balanced. In addition, advice will be provided on the checking of food labels so that specific food item can be avoided.
There are special milk formulas for babies who are allergic to milk and/or soya. The doctor may prescribe medicines depending on the severity of the food allergy and the patient’s individual circumstances. The commonly prescribed medicines are anti-histamines which counteract the histamine release in an allergic reaction. Anti-histamines are suitable for mild allergies but are unsuitable for small children and patients who have fits. They cannot be used to manage severe allergic reactions or anaphylaxis.
Severe food allergies or anaphylaxis is managed with adrenaline which keeps the airways open and reverses any drastic fall in blood pressure. The adrenaline comes in the form of auto-injector pens. Treatment should be sought at the Accident and Emergency (A & E) department of a hospital after using an adrenaline auto-injector pen. It is recommended that children with food allergies should carry two doses of adrenaline as more than 10% of children who present at A & E departments with severe food allergies or anaphylaxis receive a second dose.
It is essential that children, their carers and teachers are provided with information on the usage of the medicines prescribed.
Prevention
The prevention of food allergies is possible if the causative food item is identified. However, it is easier said than done. General measures can be taken to reduce the likelihood of food allergies. Exclusive breastfeeding especially in the first four to six months of life has been reported to reduce the incidence of allergies. Patients who have a strong family history of allergies are usually advised to avoid smoking during pregnancy and to breastfeed exclusively.
Parents should be careful and introduce new food one at a time to the baby’s diet. If there are any clinical features of an allergic reaction, the doctor should be consulted. When a food allergy has been confirmed by tests, the most effective way of prevention is to avoid the food item altogether.
It is important to remember if all potentially allergy-provoking foods are avoided after the baby has stopped breastfeeding, it is more likely to cause malnutrition. A nutritionist would be helpful in providing advice on alternative food items that have similar nutritional value. Whenever there is doubt, it is advisable to consult the doctor.
