CLINICAL: NUTRiTION Peer reviewed Marianne Williams BSc Hons RD MSc Allergy NHS and Private Specialist Allergy and IBS Dietitian
Managing food allergies Key learning points: u Different kinds of food allergy and their immune reactions u Dietary interventions for food allergies u Testing for food allergies
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llergic diseases are one of the most common causes of chronic illness in developed countries with food allergy emerging as a substantial public health concern over the last 10-15 years.1,2 In the UK it is predominantly addressed in primary care with most cases being diagnosed and treated by GPs.3-5 Indeed, among the general public, food allergy is perceived to be very common, with some research suggesting that 34.9% of people will report adverse reactions to a food at some point in their life.6 However, UK data suggests that in fact only 1.4-1.8% of adults7 and 5-6% of young children suffer with true food allergy.8-10 Some of the confusion may arise from the common misconception that all reactions to food are due to ‘allergy’. In fact, reactions to food can be caused by both allergic and non-allergic responses. Fundamentally, true ‘allergy’ involves the immune system and is caused by an immune reaction to a protein molecule. Conversely, non-allergic reactions do not involve the immune system and instead may be due to other causes such as pharmacological effects, enzyme deficiencies, chemicals occurring naturally in foods, or chemicals added to foods.11-13 To help differentiate, in 2003 the World Allergy Organisation developed a helpful and clear nomenclature using the umbrella term, ‘Food Hypersensitivity’14 (see Figure 1).
Types of food allergy Food allergy is divided into two categories: 1. Immunoglobulin E reactions (IgE reactions) These can be tested with skin prick tests and specific IgE blood tests.8,15 They tend to present almost immediately or within minutes. These reactions can be potentially dangerous, with patients suffering a range of possible symptoms. 2. Non-immunoglobulin E reactions (non-IgE reactions) These are generally delayed reactions taking from one to 48 hours to materialise.12 These reactions do not lead to anaphylaxis
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and, although often unpleasant and distressing, they do not tend to be dangerous. Non-IgE allergy appears to be caused by a different part of the immune system, eg. T cells and eosinophils, and although endoscopy may be helpful in diagnosing eosinophilic disease, more research is needed to fully elucidate the mechanism behind many non-IgE reactions.12,13 At present there are few tests for this form of allergy and dietary elimination and reintroduction is the mainstay of diagnostic procedure.12,13,16 It is in fact possible for patients to suffer with both types of allergy concurrently. For example, dairy allergy can cause IgE responses resulting in immediate reactions, eg. acute urticaria or angioedema, while also causing non-IgE delayed reactions several hours later, resulting in symptoms such as diarrhoea, abdominal pain and atopic dermatitis.13
What are the most common foods to cause allergic reactions? Cows’ milk, egg, soya, ground nuts, tree nuts, wheat, fish and shellfish are the most common cause of allergic reactions in both children and adults9,12,17,18 (see Table 1). However, it is important to keep an open mind, as many foods have the potential to cause allergic reactions.
TABLE 1. FOODS MOST COMMONLY IMPLICATED IN FOOD ALLERGY Cows' milk Hen's egg Soya bean Peanuts Tree nuts Wheat Fish Shellfish
Nursing in Practice January/February 2014
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