[ Handbook ]

Food Allergy

Written Dr Cassim Motala

 

Clinical Manifestations 1. IgE mediated reactions 2. Non-IgE mediated reactions Diagnosis 1. Laboratory tests 2. EliminationElimination-Challenge Testing Management 1. Avoidance of Offending Foods 2. Specific Allergies 3. Drug Treatment 4. Medic Alert Allergies

 

Food allergy is most prevalent during early life. It is less common after the age of 3 years. The estimated incidence of food allergy in the general population varies between 0.5% and 6%. In selected groups such as children with eczema the prevalence may be as high as 25%.

True food allergy always involves an immune mechanism (IgE or non-IgE mediated) and should not be confused with the many causes of intolerances to food such as lactase deficiency, toxins contained in contaminated foods, food additives (e.g. tartrazine) and naturally occurring chemicals in food (e.g. tyramine in cheese). Although nearly every food has the potential of causing allergy, the number of foods documented by challenge testing to induce symptoms is limited (Table 1).

Foods derived from the same biologic family may share the same or similar allergenic determinants and induce cross-reactions in sensitive patients. For example, the allergens contained in soya protein and peanuts are similar; a patient who develops IgE to one of these foods is very likely to cross-react to the other. Tables 2 and 3 list some of the food families and groups that are noted for their cross-reactivity.

Table 1

Common Food Allergens
INFANTS AND YOUNG CHILDREN	OLDER CHILDREN AND ADULTS
Egg White Cow's milk Wheat Soya protein Peanuts Fish	Fish Shellfish Peanuts Tree nuts (almonds, cashews etc.) Tomatoes Chocolates

A. Clinical Manifestations

Index

1. IgE-mediated Reactions

Cutaneous reactions such as morbilliform pruritic rash, eczema, acute urticaria and angioedema are the most common manifestations. Food allergy is rarely responsible for chronic urticaria.

Gastrointestinal symptoms, including nausea, vomiting, abdominal pain and cramping are the second most common. Diarrhoea is found less frequently. IgE-mediated food allergy may cause infrant colic in 10% to 15% of cases.

Respiratory manifestations such as asthma and allergic rhinitis are relatively less common. They usually occur in association with either cutaneous and/or gastrointestinal symptoms and seldom as isolated manifestations.

Anaphylaxis is the most serious manifestation. Foods most likely to cause anaphylaxis include peanuts, tree nuts, milk, eggs and fish. Certain foods such as celery, shellfish and wheat have been implicated in exercise-induced anaphylaxis.

2. Non-IgE-mediated Reactions

These are relatively infrequent. Clinical experience suggests that non-IgE reactions occur mainly to cow's milk, they are uncommon for egg and rare for peanut as well as other foods.

Gastrointestinal manifestations such as enteropathy and colitis predominate in this subgroup of food allergy. Food-induced enteropathy commonly presents in infants, is most often caused by cow's milk and soya protein, and presents with protracted vomiting and diarrhoea complicated by dehydration. Chronic enteropathy may also present with failure to thrive or protein losing enteropathy. Cow's milk and soya protein may also cause allergic colitis in infants.

These patients present with occult or gross blood in their stool but are otherwise well. In addition, allergies to cow's milk, soya protein, egg and wheat can present as malabsorption syndromes. Coeliac disease is a more extensive malabsorption syndromes. Coeliac disease is amore extensive malabsorption syndrome resulting from sensitivity to gluten found in wheat, rye, oat and barley. Eighty-five percent of patients with dermatitis herpetiformis have gluten-sensitive enteropathy.

Rarer non-IgE manifestations include arthritis, migraine and Heiner's syndrome. Other symptoms which have been implicated but not substantiated include fatigue, hyperactivity and enuresis.

Table 2
Classification of Foods from Animal Sources

BIRDS	CRUSTACEANS	FISH	MAMMALS	MOLLUSCS
Chicken Duck Goose Turkey Guinea hen Squab Pheasant Partridge Grouse	Crab Crayfish Lobster Shrimp	Sturgeon Hake Anchovy Sardine Herring Haddock Bass Trout Salmon Whitefish Scrod Shad Eel Carp Codfish Halibut Catfish Sole Pike Flounder Drum Mullet Weakfish Mackerel Tuna Pompano Bluefish Snapper Sunfish Swordfish	Beef Pork Goat Mutton Venison Horsemeat Rabbit Squirrel	Abalone Mussel Oyster Scallop Clam Squid

 

 

Table 3
Classification of Foods from Plant Sources

APPLE BANANA BEECH CASHEW   Apple Pear Quince   Banana Plaintain   Beechnut Chestnut   Cashew Pistachio Mango   CITRUS GOURD GRASS & GRAINS GINGER   Citron Grapefruit Kumquat Lemon Lime Orange Tangelo Tangerine   Pumpkin Squash Cucumber Cantaloupe Muskmelon Honeydew melon Persian melon Casaba Watermelon   Bamboo Barley Corn Malt Millet Oat Popcorn Rice Rye Sorghum Sugarcane Wheat   Ginger Tumeric Cardamon   LEGUMES LILY LAUREL MINT   Acacia Broadbean Black-eyed bean Chick-pea Common beans Kidney Lima Navy String bean Lentil Licorice Pea Peanut Senna Soybean Tamarind   Asparagus Onion Leek Chive Aloe   Avocado Cinnamon Bay leaf   Mint Peppermint Spearmint Thyme Sage Marjoram Savory   MULBERRY MUSTARD MYRTYLE MORNING GLORY   Mulberry Fig Hop Breadfruit   Mustard Cabbage Cauliflower Broccoli Brussels sprouts Turnip Rutabaga Kale Collard Celery Cabbage Kohlrabi Radish Horseradish Watercress   Allspice Cloves Paprika Guava   Sweet potato Yam   NIGHT SHADE OLIVE ORCHID PALM   Bell pepper Cayenne pepper Eggplant Ground cherry Melon pear Potato (white) Tobacco Tomato   Green olive Ripe olive Red pepper Green pepper Bell pepper Chilli Tabasco Pimento   Vanilla   Coconut Date Sago     ROSE WALNUT BIRCH PARSELY   Rasberry Balckberry Loganberry Boysenberry Dewberry Strawberry   English walnut Black walnut Butternut Hiickory nut Pecan   Filbert Hazelnut   Parsely Parsnip Carrot Celery Celeriac Caraway Anise Dill Coriander Fennel

B. Diagnosis

Index

1. Laboratory Tests

The diagnosis of food allergy is easy when the adverse reaction occurs soon after ingestion of an uncommonly used food item (immediate reaction) but more difficult if the reaction occurs several hours or days later (delayed reaction), or if a commonly used food is involved. In this situation a variety of tests (Skin prick test, RAST, etc.) can be used. The RAST Paediatric Food Mix fx5 (Pharmacia), which is a mixed-allergen test containing milk, soya, fish, egg-white, wheat and peanut is a useful screening test for food allergy in small children. A positive test is RAST fx5 usually followed by specific testing for individual allergens. These tests only provide evidence that IgE sensitivity to food exists but cannot predict which sensitised patients will react clinically to food challenges. Generally both skin testing and RAST produce low false-negative rates. Therefore, these tests have a good negative predictive value but poor positive prediction for IgE-mediated food allergy.

 

2. Elimination-Challenge Testing

The mainstay of diagnosis is the demonstration of relief of symptoms on removal of a given food item and recurrence of symptoms on its re-introduction (elimination-challenge testing). Prior skin testing and/or RAST tests may help to pinpoint the foods that should be tested in the withdrawal-relief and challenge procedures. The gold standard for food allergy diagnosis is the double-blind placebo-controlled food challenge (DBPCFC). However, DBPCFC's are labour intensive and should ideally be performed in a hospital setting. Open challenge testing is particularly useful for refuting the diagnosis of food allergy. Challenges should never be performed in patients who have experienced life-threatening reactions to food. In vitro tests such as RAST are preferred in this situation. When the offending food(s) are not identified a simple elimination diet which consists of relatively non-allergenic foods (Table 4) is recommended for about 2 weeks. Should the patient's symptoms clear upon the elimination diet, food allergy is likely and thereafter foods normally taken should be introduced one at a time and response assessed. If the patient's symptoms persist on the elimination diet, food allergy is unlikely and the diagnosis should be reviewed. Figure 1 outlines an approach to elimination-challenge testing.

 

Figure 1
Flow diagram for the food elimination-challenge test.
Ref. Allergy Clinics of North America 1991;11:843-50

 

Table 4

Simple Elimination Diet Rice (cakes/cereal) Fruit (apricot, peaches, pears, apples) Vegetables (asparagus, beetroot, carrots, lettuce, sweet potatoes) Other (white vinegar, olive oil, honey, cane or beet sugar, salt, sunflower oil) NB: Not nutritionally complete; use for up to 14 days only.

 

 

C. Management

Index

1. Avoidance of Offending Foods

Avoidance is easy to prescribe but can be difficult, expensive and inconvenient to follow. The strictness of the regimen must always be balanced against the severity of the symptoms. In infants and children, it is important to eliminate as few foods as possible and for as short a period of time as possible. Cautious re-introduction of a "prohibited" food should be attempted after 6-12 months. The natural history of food allergy in many children is of gradual improvement of symptoms even though skin prick tests remain positive. Many children eventually develop tolerance to milk, wheat, vegetables, fruit and even eggs but rarely to fish and nuts. Dietary management should always be conducted in collaboration with a dietitian, not only to ensure nutritional adequacy but also to make the diet varied and interesting, thereby ensuring compliance. The risks of restrictive diets are listed in Table 5 (applies particularly to patients with multiple food allergies).

Table 5

Risks of Restrictive Diets

Starvation or malnutrition. High costs for family (society). Anxiety in the family. Overprotection of the child. Social isolation. Disappointment or anger when symptoms develop.

 

2. Specific Allergies

Children who are milk-allergic should avoid all forms of milk or milk products including casein, butter, whey, protein concentrate, curds, yoghurts, cheese, cream, buttermilk, caramel and high-protein flour. Patients who have a milk allergy and are on a milk-restricted diet will require calcium (Table 6) and vitamin D supplementation. Table 7 lists the calcium agents commercially available.

Table 6

Recommended Dietary Allowances for Calcium (Daily)
Group	Age	Calcium (mg)
Infants	0-6 months	360
	6 months	540
Children	1-10 years	800
Children and Adolescents	11-18 years	1200
Pregnant and lactating women		500

Table 7

Available Oral Calcium Agents
Brand Name	Dose	Elemental Ca++Content
Calcium Sandoz Forte	500 mg	500 mg
Calcium Sandoz Sachet	1 sachet	500 mg
Calcium Sandoz Syrup	5 ml	110 mg
Citrate	1 tablet	300 mg
Titralac	1 tablet	168 mg
Calcium Gluconate	300 mg	27 mg

Children on an egg-restricted diet will often have to eliminate grain and bakery products and this diet is likely to be inadequate in respect of the vitamin B group and iron. Egg-derived substrates (which consumers should read on packaging labels and avoid) include egg (whole or dried), egg-white, albumen, egg lecithin, vitellin, ovovitellin, livetin, globulin, ovomucoid and ovomucin. Incidentally, lecithin included in South African products is commonly derived from soya and not egg. Egg lecithin is used often in some imported products. Consumers should be aware that egg is frequently a Hidden ingredient in batters, an agent to bind breadcrumbs and flour to crumbed foods such as fish and fish cakes. It is brushed onto pastry and buns to enhance browning and may also be present in special breads and rolls/buns as well as other bakery items, cakes, cake-mixes, biscuits meringue, pancakes, doughnuts, marzipan, fruit cake icing, pies, quiches, some pastry and waffles. Other egg-containing foods include puddings, custard, whipped puddings, souffles, tartar sauce, fish cakes, meat balls and rice from Chinese restaurants. Certain sweets such as nougat, marshmallows (not all brands) sherbet and ice-cream may also contain egg-derived substrates.

Patients sensitive to peanuts require extremely strict adherence to their diets. Many Chinese dishes, soups, marzipan and health foods contain peanuts. Peanut oil, which contains peanut lipids and hydrolysed peanut protein is usually non-allergic and tolerated by moderately sensitive individuals. Soya bean and soya products are found in infant formula cereals, baked goods, crackers, canned tuna, soups and sauces. Patients with soya bean lose their sensitivity within 1-3 years of initial challenge. Soya bean oil, like peanut oil, is also generally non-allergenic.

Wheat elimination diets are particularly difficult to maintain. Children on wheat-restricted diets are severely limited in their choice of foods. Cereal, breads, pastas, crackers, sauces, lunch-meat, snack foods and sweets should be avoided. These children can usually eat oats, rye, barley or corn as substitutes. It is important that children should recognise ingredients that indicate the presence of wheat proteins, e.g. gluten, wheat starch, bran, vegetable starch, modified food starch or vegetable gum. Children on a wheat-restricted diet should be evaluated for possible nutritional deficiencies of vitamin B and iron.

Certain patients tend to react to cross-reacting foods. The ability to react depends on whether the patient is sensitive to shared allergens or to allergens that are species specific. Food-allergic patients should be educated about food grouping and caution should be advised when first eating other members of the same food group. (See Tables 2 and 3).

 

3. Drug Treatment

Drug treatment in food allergy is indicated when symptoms persist despite attempts at an elimination diet. This may occur if the diagnosis is incomplete, if exposure is unavoidable, of if the patient deviates occasionally from the prescribed diet.

Currently available drugs for the treatment of food allergy include oral sodium cromoglycate (Nalcrom) and ketotifen (Zaditen). Oral sodim cromoglycate in liquid form (only available in Europe) appears to be more effective than the powder form and much easier to administer in infants. Sodium cromoglycate and ketotifen may even normalise gut permeability in certain patients. Drug therapy may also be necessary to relieve symptoms other than those of the gastrointestinal tract e.g. bronchodilators and anti-inflammatory treatment for asthma, and topical steroids for eczema. Anti-histamines are useful in food-induced urticaria and adrenaline is necessary for life-threatening anaphylaxis.

 

4. Medic Alert

Patients who have experienced a life-threatening reaction to any food should wear Medic-Alert discs. They also should be provided with an antihistamine and a preloaded adrenaline syringe (Anaguard or Epipen) or adrenaline metered dose inhaler (Medihaler-Epi) for emergency use when they are inadvertently exposed to the offending food.

Medic Alert Foundation
320 Plein Street
CTC Building
P.O. Box 4841
Cape Town 8001

Telephone: (021) 461 7328
Fax: (021) 461 6654

Internet:
http://www.cia.co.za/charity/medalert/medalert.htm