FOOD ALLERGY
· Allergy is one of the health hazards, which is generally regarded as any abnormal reaction of a person’s immune system to a foreign substance e.g. pollen grain/ food constituent.
· It is defined as any hypersensitivity reaction towards food with a demonstrated immunological basis.
2. Classification of Allergies
6. Diagnosis
7. Treatment
Prevalence of food allergy
· Adults: 1.4% - 2.4%
· Children < 3 years: 6%
· Atopic dermatitis (mild/severe): 35%
· Asthmatic children: 6 - 8%
· Prevalence depends on: Genetic factors, age, dietary habits, geography and diagnostic procedures.
· Major allergenic foods (>85% of allergy).
· Children: milk, egg, soy, wheat, other depending on geographical area.
· Adult: peanut, nuts, shellfish, fish.
· An adverse reaction to a food or food component (often a protein) involving reactions of
the body’s immune system (immunological reactions).
· The term “food allergy” should only be used to identify true, immunologically based food allergies - those which affect the body’s immune system.
· Examples would be allergic reactions to common foods such as cow’s milk, eggs peanuts,
and many other.
· It is preferred over the alternative term, “Food hypersensitivity,” which has been used to describe this type of reaction as well as other types.
TYPES OF FOOD ALLERGIES
Allergic responses may be organized into four categories noted as Types I-IV.
Type I Allergies
· Food anaphylaxis (The Greek word anaphylaxis means “against protection and refers to allergic reactions to foreign protein molecules).
· Immediate hypersensitivity-occur within a few minutes to several hours after consumption of the offending food.
Symptom
· Release of pharmacologically active substances (mediators) such as histamine.
· Specific cells in the body known as mast cells.
· Interaction between immunoglobulin E (IgE) and food substances which cause allergic
reactions (“allergens”).
Type II and Type III
· Neither Type II nor Type III allergies have been associated with food.
· Their differences lie in the time of onset, from four to six hours after exposure.
Type IV Allergies
· Delayed (over hours rather than minutes) hypersensitivity – type allergic responses.
· “Cellular hypersensitivity,”
· Reaction of certain sensitized cells, usually lymphocytes, to the specific chemical substance that triggers the allergic reaction, the allergen.
· Type IV allergies may involve food, but in comparison of the reactions is poorly understood at the molecular level.
· 6 to 24 hours after consumption of the offending food.
· Immediate allergies.
· Delayed allergies.
Immediate Allergies
· Are less common in occurrence.
· Easily recognizable because of immediate symptoms.
· Clinical features/ symptoms-Nausea, abdominal pain, vomiting. etc.
· Certain late- phase reactions are eczema, etc.
· Violent responses and life threatening reaction in some cases.
· It can be treated with drugs temporarily but is a permanent allergy.
Delayed Allergies
· Not easily recognizable, takes few hours to days to show symptoms.
· Involves type II, III or IV but do not involve IgE i.e. type I reactions.
· Symptoms are of low grade- headache, indigestion, abdominal pain, fatigue etc., i.e. not fatal.
· This is very much prevalent in occurrence.
ALLERGIC FOODS
· Apricots, Asparagus, Bananas, Barley, Carrots, Beets, Lettuce, Millet, Oats, Peaches, Rice, Squash and sweet potato.
1. Cow’s Milk Allergy
· Prevalence 2.0 - 2.5% worldwide.
· Proteins: Casein 80% + 20% Whey.
· Several allergens have been described.
· Major: casein and beta-lactoglobulin
· Minor: whey
· High degree of cross-reactivity between cow, sheep, goat’s milk.
2. Hen’s Egg Allergy
· Composed of egg white and egg yolk.
· Both have multiple allergens, Egg white has more allergens than egg yolk (major).
· Ovalbumin, lysozyme (minor).
· Cross-reactive with other birds, like duck.
3. Fish Allergy
· Higher prevalence in fish-eating countries.
· Parvalbumin is major allergen.
· Heat-resistent, from white meat.
· Cross-reactivity with other fish.
4. Crustaceans
· Shrimp is most studied.
· Tropomyosins major allergens.
· Ntat-resistent allergensP.
· Present in multiple crustacean.
5. Peanuts
· Family Leguminosae.
· Children increasingly exposed at young age.
· Multiple allergens described (Ara h 1, Ara h 2).
· Responsible for most of food-induced anaphylaxis cases.
Types of Food
· Allergic reaction can be provoked by skin contact with poison plants.
· Chemicals and animal scratches, as well as by insect stings. Ingesting or inhaling substances like pollen.
· Animal dander, molds and mildew, dust, nuts and shellfish, may also cause allergic reaction.
· Mast cells release histamine when an allergen is encountered.
· The histamine response can produce sneezing, itching, hives and watery eyes.
Symptoms
· Manifestations of allergy can occur in any part of the body.
· Skin manifestations may includes dermatitis, oedema, fever, blisters, pruritus and urticaria (rashes).
· Common gastrointestinal manifestations, include cheilitis, stomatitis, colic in infants, abdominal distentions, constipation, diarrhoea, dyspepsia and nausea and vomiting.
· Respiratory symptoms include allergic rhinitis, asthma, bronchitis and nasal polyps.
· Neurologic symptoms such as migraine, neuralgias and tension fatigue syndrome (anxiety, fatigue, irritability, muscle and joints ache restlessness, stomach pain).
DIAGNOSIS
Dietary History
· Patient is given a diary in which he should record all foods eaten and should also record any disturbances occurring due to the food allergy.
Provocative test
· Patients are given a small quantity of the suspected food.
· The test should be conducted for a minimum of 3 times before obtaining confirmative results.
· Should not be conducted in patients who develop severe allergic reactions as it may prove dangerous.
Elimination test
· Patient omits one suspected food each day and keeps record of signs and symptoms.
· Adapted in infants and children because of the limited variety of foods they eat.
· Difficult and complicated
· Suited for investigation of patients in hospitals with a dietetic department and physician experienced in study of allergy.
Radio Allergosorbent test
· It is the skin prick test that aim to detect the presence of IgE antibodies.
· Aim to measure the binding of IgE to allergens such as milk, eggs or fish.
· An arbitrary score from 0-4 is given. Allergic patients usually have a score above 2.
· These tests are expensive and not very informative.
Skin Test
· In intra dermal test minute quantities of extracts containing suspected antigens are packed into the skin over the arm.
· In scratch test a small amount of the solution containing the antigen is placed into a series of scratches made into the skin.
· In patch test the antigen is applied to a piece of filter paper over the skin and covered with cellophane and kept for 24 hours.
· If a red inflammation or hive like wheal appears at the site of contact, the food is suspected to contain the allergen.
· Sometimes oedema or erythema due to vasodilation is seen.
X-ray
· An X-ray of the GI tract immediately after ingestion of suspected food, admixed with BaS04 will sometimes reveal changes associated with smooth muscle spasm.
· This only shows the abdominal distress after taking food.
TREATMENT
Elimination diets
1. Simple exclusion diet: Single food like milk, egg, or wheat is suspected, patients are advised how to consume a diet, free of these.
ü This is not simple in practice.
ü Exclusion of food like milk in children, require dietary expertise to ensure that dietary requirements are met.
2. Multi Exclusion Diet: It is not clear from dietary enquiry or simple exclusion diet which foods are responsible, a complex exclusion diet has to be tried on trial and error basis).
(a) Initial exclusion diets: Initially a wide range of foods which may provoke intolerance is removed from diet and after a period of time, reintroduced singly into the diet so the offending item is identified.
(b) Graduated Exclusion diet: The number of foods excluded from a diet is gradually increased.
Denaturation
3. Denaturation can help eliminate allergic activity of food, for e.g., patient may be sensitive to raw milk but boiled may be suitable.
Hypersensitation
4. Some physicians have been trying to help patients by giving repeatedly small doses of the allergen either by mouth or injection in the hope that their sensitivity may disappear.
Drugs
5. A number of drugs that mitigate the symptoms of allergy are available.
6 . Antihistamines - urticaria and angioedema. Although drugs causing somnolence are effective, likely to cause discomfort when taken regularly.
7. Bronchodilator drugs - bronchial spasms in attacks of asthma.
8 . Corticosteroids are highly effective in prevention of attacks. But they can cause adverse effects when used in long term especially in children.
Dietary advice
9. Patients who are sensitive to eggs may be able to take egg yolk as the egg white is the main allergen.
Facts about food allergies
· Food allergy is not common but can be serious.
· Food allergy differs from food intolerance, which is far more common.
· The more frequent types of food allergies in adults differ from those in children.
· Children can outgrow their food allergies, but adults usually do not.
· The diagnosis of food allergy is made with a detailed history, the patient’s diet diary, or an elimination diet.
· Food allergy is treated primarily by dietary avoidance.
PREVENTION
· Food allergy is treated by avoiding the foods that trigger the reaction.
· Advice client that, once he and his healthcare provider have identified the food(s) to which he is sensitive, he must remove them from his diet.
· Encourage him to must read the detailed ingredient lists on each food he is considering eating.
Difference Of Food Allergy And Food Intolerance
· Sometimes, a reaction to food is not an allergy at all but another type of reaction called
“food intolerance".
