Food allergies and intolerances

Food allergies and intolerances

A 5-year-old boy is rushed to hospital with sudden onset of facial swelling, hoarseness of voice and difficulty breathing, after ingestion of cake at a birthday party. This is a typical example of adverse food reactions, commonly encountered by emergency clinicians.

Adverse food reactions are classified as either food intolerance or food allergies.

It is important to differentiate between the two, as food allergy which is immune mediated, is more severe as it can involve multiple organ systems of the body including skin, respiratory, gastro-intestinal and cardio-vascular system. It can also lead to life threatening hypersensitivity reaction, as described in the fore-mentioned scenario. Not only this, patients with confirmed IgE-mediated allergy are at risk of developing asthma and allergic rhinitis later on.

Symptoms of gastrointestinal tract can be variable, ranging from vomiting, diarrhoea and spitting up to more complex manifestations like failure to thrive, proctocolitis and enterocolitis. Nasal congestion, rhinorrhoea and wheezing, hypotension, arrhythmias and atopic dermatitis are the features of respiratory, cardiovascular and dermatological systems.

Food intolerance, in contrast, is non-immune mediated, milder and its involvement is generally limited to gastrointestinal tract. It generally results from lack of a specific enzyme like lactase deficiency, or bacterial over growth, presence of food additives, or naturally occurring substances in certain foods like amines in cheese and caffeine in chocolates and coffee.

Although adverse food reactions are reported by more than 1/3rd parents, the rates of verifiable food allergies are much lower. The prevalence of true food allergy is 6 to 8% in children and 3 to 4% in adults. Peak incidence occurs in infancy. Most allergies are generally outgrown, but peanut and tree nut allergies tend to persist.

The most common food allergens are cow milk protein, soy protein, egg, chicken, fish, nuts, wheat, rye and barley. Allergy to pollen can lead to allergy to certain fruits and vegetables like apple, banana, kiwi, potato and celery.

Cross-reactivity occurs when the proteins in one substance are like the proteins in another. There is a high degree of cross-reactivity between cow's milk and milk from other mammals, between peanuts, legumes and tree nuts, and between pollen and fruits. Previously it was recommended to avoid all cross-reactive foods, but this practice has been abandoned and can lead to the exclusion of multiple foods from the diet. Whilst this might be unhealthy for an adult, it can be positively harmful in a child and can lead to severe nutritional deficiencies. The tools available for diagnosing food allergy includes a detailed history, physical examination, trial of elimination diets, diet diary, skin prick testing and specific IgE testing.

The history should focus on identifying whether the adverse food reaction is an allergy or intolerance. Other details like type and quantity of food, association with exercise, similar reactions in past, personal or family history of eczema, asthma or allergies should be sought.

A negative skin prick test rules out the possibility of Ig-E mediated form of food allergy. On the other hand, a positive skin test should further be evaluated by more definitive tests like specific Ig-E tests, food elimination and challenge tests, as many patients with positive skin prick test do not react when the alleged food is ingested. Therefore, before labelling a child as being allergic to a certain type of food, it is mandatory to be sure that true food allergy is actually present. For this elimination diets, followed by food challenge, performed by an allergist, under control settings should be performed.

This call to put emphasis on the fact, that broad exclusionary diets such as avoidance of all legumes, cereals, grains, nuts, animal products is not warranted unless proven otherwise.

The mainstay of treatment is avoidance of allergen. This requires extensive patient education, including correct reading of food labels, preparation of safe food at home by avoiding cross contamination, avoiding aerosolisation of allergen by extensive handling like grinding or roasting. Also, an allergen may be a component of non-food item like vaccine, drug or cosmetic. Similarly, breast milk might be a vessel for exposing a new-born to a certain allergen, therefore a mother can be put on a restrictive diet. As most of the children outgrow allergies they should be evaluated by an allergist on yearly to two yearly bases for the development of tolerance. This is done by testing specific IgE levels along with certain clinical criteria, if proven to be tolerant; the allergen food is re-introduced into the diet.

Children with severe hypersensitivity reaction and those with asthma along with IgE mediated food allergy should have an epinephrine pen available all times along with a written emergency plan to avoid life threatening complications and must be closely followed by an allergist and a nutritionist.

With thanks to Dr Madiha Maqsood Aaqib Ullah at Medcare Hospitals & Medical Centers.
Call 800MEDCARE or visit www.medcare.ae

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