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
A
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
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What type of dietary interventions are used in food allergy? A range of dietary interventions can be used to help diagnose food allergy. Dietary restriction of the culprit food or foods is the mainstay of treatment. However, these are complex diets for patients to follow and require supportive literature with guidance on alternative foods, menus, recipes, how to avoid cross contamination at home and when eating out, and how to read labels to ensure compliance.12 Hence, it is always advisable to involve a registered dietitian in the treatment of these patients.
‘IgE reactions are immediate and have the potential to be dangerous while non-IgE reactions are delayed and are not life threatening’ Most patients will require regular follow up every 2-4 weeks with either one-to-one or telephone support. This is especially important with non-IgE allergy where the culprit food may not be obvious and it is therefore vital that the dietary intervention is reassessed regularly to ensure that it is effective and remains appropriate. Often it is trial and error and patients may need to try several dietary approaches before resolving their symptoms. This is why a carefully taken comprehensive case history is essential as this will often act as a guide as to the relevant approach.19
Allergy Tests IgE testing This can be done using either or both skin prick testing and specific IgE blood testing. It is important to remember that these tests are not definitive on their own and can only be used in conjunction with a detailed clinical history. They form part of the diagnostic work-up. These tests actually only show a ‘sensitisation’ and hence it is very possible to have a positive test and yet show no clinical signs of allergy to that particular food. Indeed, if this were the case, then it is often preferable to keep that food in the diet rather than remove it based purely on the allergy test result. Ideally tests should only be conducted for a food for which there is good clinical suspicion. The magnitude of the result also does not predict the severity of the clinical reaction and it is perfectly possible to have a small result and a very severe reaction or visa versa.
IgE Skin Prick Testing Although the National Institute of Health and Care Excellence (NICE) guidance in 2011 stated that it was safe to conduct skin prick testing in primary care with the correct access to resuscitation equipment and if carried out by a suitably trained healthcare practitioner19 it is still rare to have access to this test at a GP surgery in the UK. Generally a referral to secondary care is necessary. This test is actually the cornerstone in the evaluation of food sensitisation and offers an in-office, rapid and sensitive assessment of allergen sensitisation.8
Specific IgE Testing Blood can be taken at the GP surgery and sent to the pathology lab for assessment of its IgE antibody status.
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Specific IgG Testing There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance and patients could end up with incorrect dietary advice which could leave them unnecessarily nutritionally compromised. World allergy organisations such as the European Academy of Allergology and Clinical Immunology (EAACI) state that, “IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints.”20
Alternative allergy testing These may include vega testing, hair analysis, kinesiology, cytotoxic food testing, leukocytotoxic test, Nambudripad’s allergy elimination. All these tests are expensive and all have little or no credible evidence to support their use.
Quality of life and food allergy Although the majority of children will outgrow their allergy18,21 a proportion will not and it is rare for adult allergy to resolve. There is no cure or preventative treatment other than strict avoidance of the implicated food or foods. Depending on the symptoms associated with the allergy case history, some patients will need to carry adrenalin emergency treatment in case of accidental exposure. Thankfully mortality is very rare. However, quality of life is often severely affected with profound psychosocial impact on many patients and their families.22
Allergy guidelines In recent years there have been several guideline publications which have summarised the current evidence base and should help to standardise care.13,19,23-25 The most useful of these for UK primary care nurses are the 2011 UK NICE Guidelines, ‘Diagnosis and assessment of food allergy in children and young people in primary care and community settings’.19 For anyone dealing with allergy in primary care, this is an invaluable document and makes recommendations for interpreting signs and symptoms, the use of suitable allergy tests, when to refer onwards for specialist guidance, as well as how to take an essential allergy-focused clinical history. Cows’ milk protein allergy (CMPA) is by far the most prevalent food allergy in most regions of the world, with research suggesting that it affects 2-3% of infants in their first year of life in developed countries and with 2.16% of infants in the UK reported to suffer with CMPA.26-29 Indeed, this food allergy presents a particular challenge in primary care and recent research shows that it is significantly under-diagnosed and poorly managed.3 In response, the UK Milk Allergy in Primary Care (MAP Guideline) was produced in 2013, which gives a clear pathway for the initial clinical recognition and the on-going management of those with non-severe, non-IgE mediated CMPA which will form the majority of patients suffering with CMPA.25
In conclusion Allergy can affect both adults and children and involves the immune system using either IgE or non-IgE reactions. IgE reactions are immediate and have the potential to be dangerous while non-IgE reactions are delayed and are not life threatening. The dietary interventions for either form of allergy are complex and require regular support and comprehensive literature to ensure
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the United States: report of the NIAID-sponsored expert panel. J
figure 1. Food sensitivity and allergy
Allergy Clin Immunol. [Consensus Development Conference
Practice Guideline]. 2010 Dec;126(6 Suppl):S1-58.
14. Johansson S, G, O. et al. Revised nomenclature for allergy for global
Food Hypersensitivity
Nomenclature for food hypersensitivity
use: Report of the Nomenclature Review Committee of the World Allergy Organisation, October 2003. Journal of Allergy & Clinical Immunology. 2004;113(5):832-6. 15. Bousquet J, Heinzerling L, Bachert C, Papadopoulos NG, Bousquet
Food Allergy
Non-allergic food Hypersensitivity
PJ, Burney PG, et al. Practical guide to skin prick tests in allergy to aeroallergens. Allergy. [Practice Guideline]. 2012 Jan;67(1):18-24. 16. Meyer R, Schwarz C, Shah N. A review on the diagnosis and management of food-induced gastrointestinal allergies. Current Allergy & Clinical Immunology. 2012;25(1).
IgE-mediated food allergy
Non-IgE-mediated food allergy
17. Sampson HA. Update on food allergy. J Allergy Clin Immunol. [Review]. 2004 May;113(5):805-19; quiz 20. 18. Sicherer SH, Sampson HA. Food allergy. J Allergy Clin Immunol.
Revised nomenclature for allergy for global use: Report of the Nomenclature Review Committee of the World Allergy Organisation, October 2003 Proposed for use by the European Academy of Allergy and Clinical Immunology
[Review]. 2010 Feb;125(2 Suppl 2):S116-25. 19. NICE. National Institute for Health and Clinical Excellence. Food Allergy In Children and Young People: Diagnosis and assessment of food allergy in children and young people in primary care and community settings. NICE clinical guideline 116. February
compliance and help improve quality of life. Thankfully there are now several useful national and international guidelines which can help primary care nurses when dealing with food allergy in their patients. The use of a registered dietitian is always preferable.
2011;London. 20. Stapel S, Asero R, Ballmer-Weber B, Knol E, Strobel S, Vieths S, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Allergy. 2008;63(7):793-6. 21. Sicherer SH. Epidemiology of food allergy. J Allergy Clin Immunol.
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