الفهرس 
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Abstract
Adverse reactions to food consist of any untoward reaction following the ingestion of a food or food additive and are classically divided into food intolerances, which are adverse physiologic responses, and food hypersensitivities, which include adverse immunologic responses and allergies.
1- Food allergy:
Food allergies are immunologically mediated adverse reactions to foods. Such allergies can result in disorders with an acute onset of symptoms following ingestion of the triggering food allergen (eg, anaphylaxis), as well as in chronic disorders (eg, atopic dermatitis).
The most abnormal immunologic reaction to food is immediate immunoglobulin (Ig) E–mediated hypersensitivity to food, also termed a type I reaction, involved in the pathogenesis of many cases of asthma, rhinitis, urticaria, and atopic eczema as well as GI ARF. Delayed reactions following immediate IgEmediated hypersensitivity occur in selected individuals and are characterized by an enhanced cell infiltration of the tissue with inflammatory cells and subsequent tissue damage. These and other cell-mediated immune reactions to food antigens may also operate in the GI tract and are believed to play a role in milk and soy protei enteropathies and in celiac disease. Immunologic reactions to foods can also involve “mixed IgE- and non–IgE-mediated” and other mechanisms than classic immediate or delayed hypersensitiviy.
Risk factors for food allergy
Include
a) Hereditary, genetic and molecular risks.
b) Changes in diet also play arole
c) Allergen exposure.
A number of IgE-, cellular-, and mixed IgEe and cell-mediated food hypersensitivity disorders have been described. Each include cutaneous, respiratory and gastrointestinal manifestations.
Cutaneous manifestations
Acute urticaria and angioedema are among the most common symptoms of food-induced allergic reactions. Chronic urticaria and angioedema much less common.
Respiratory manifestations
Acute respiratory symptoms caused by food allergy generally represent isolated IgE-mediated reactions, whereas chronic respiratory symptoms represent a mix of IgE- and cell-mediated reactions. Isolated rhinoconjuctivitis, ashma and heiner’s syndrome are the most common manifestations.
Gastrointestinal manifestations
The pollen-food allergy syndrome (oral allergy syndrome) is elicited by a variety of plant proteins that cross-react with airborne allergens. Allergic eosinophilic esophagitis (AEE) and allergic eosinophilic gastroenteritis (AEG) might be due to IgE mediated food allegy, non IgEmediated food allergy, or both
Food proteineinduced proctocolitis is another of the eosinophilic gastrointestinal disorders but only appears to involve a noneIgE-mediated mechanism. Food proteine- induced enterocolitis syndrome is a cellmediated hypersensitivity disorder most commonly seen in infants before 3 months of age.
Prick skin tests and in vitro laboratory tests are useful for demonstrating IgE sensitization. Many fruits and vegetables require testing with fresh produce because labile proteins are destroyed during commercial preparation. A negative skin test result virtually excludes an IgE-mediated form of food allergy. Conversely, the majority of children with positive skin test responses to a food do not react when the food is ingested, so more definitive tests, such as quantitative IgE tests or food elimination and challenge, are often necessary to establish a diagnosis of food allergy. Serum food-specific IgE levels ≥15 kUA/L for milk (≥5 kUA/L for children ≤1 yr), ≥7 kUA/L for egg (≥2 kUA/L for children <3 yr), and ≥14 kUA/L for peanut are associated with a >95% likelihood of clinical reactivity to these foods in children with suspected reactivity.
Unfortunately, there are no laboratory studies to help identify foods responsible for cell-mediated reactions. Consequently, elimination diets followed by food challenges are the only way to establish the diagnosis.
Appropriate identification and elimination of foods responsible for food hypersensitivity reactions are the only validated treatments for food allergies. Complete elimination of common foods (milk, egg, soy, wheat, rice, chicken, fish, peanut, nuts) is very difficult because of their widespread use in a variety of processed foods.
A number of clinical trials are under way, evaluating the use of oral immunotherapy and sublingual immunotherapy for the treatment of IgE-mediated food allergies (milk, egg, peanut). In addition, other forms of therapy, such as anti-IgE immunoglobulin therapy, engineered recombinant food protein vaccines, and herbal formulations, are being evaluated and may provide more definitive means of treating food allergies or at least raising the threshold for adverse reactions. In addition, tolerance may be generated by heating (cooking) the food (milk).
There is no consensus as to whether food allergies can be prevented. At present there is insufficient evidence to support the practice of restricting the maternal diet during pregnancy or breast-feeding or of delaying introduction of various allergenic foods to infants from atopic families. Studies suggest that exclusive breast-feeding and/or supplementation or use of hydrolyzed milk-based formulas for the first 4-6 months of life may reduce allergic disorders (e.g., atopic dermatitis) in the first few years of life in infants at high risk for development of allergic disease. However, the value of further restrictions cannot be supported by the current medical literature. Because some skin preparations contain peanut oil, which may sensitize young infants, especially those with cutaneous inflammation, such preparations should be avoided.
In general, most infants and young children outgrow or become clinically tolerant of their food hypersensitivities.
Food intolerence
Non-allergic food hypersensitivity is the medical name for food intolerance, loosely referred to as food hypersensitivity, or previously as pseudo-allergic reactions. Non-allergic food hypersensitivity should not be confused with true food allergies.
Estimates of the prevalence of food intolerance vary widely from 2% to over 20% of the population.
Food intolerance (FI) are all other adverse reactions to food. Subgroups of FI are enzymatic (e.g. lactose intolerance due to lactase deficiency), pharmacological (e.g. reactions against biogenic amines, histamine intolerance), and undefined food intolerance (e.g. against some food additives).
Food intolerance can present with symptoms affecting the skin, respiratory tract, gastrointestinal tract (GIT) either individually or in combination. On the skin may include skin rashes, urticaria
angioedema, dermatitis, and eczema. Respiratory tract symptoms can include nasal congestion, sinusitis, pharyngeal irritations, asthma and an unproductive cough. GIT symptoms include mouth ulcers, abdominal cramp, nausea, gas, intermittent diarrhea, constipation, irritable bowel syndrome, and may include anaphylaxis.
Diagnosis is made using medical history and cutaneous and serological tests to exclude other causes, but to obtain final confirmation a Double Blind Controlled Food Challenge must be performed. Treatment can involve long-term avoidance, or if possible re-establishing a level of tolerance.
The antigen leukocyte cellular antibody test (ALCAT) has been commercially promoted as an alternative, but has not been reliably shown to be of clinical value.
Individuals can try minor changes of diet to exclude foods causing obvious reactions,
Over a period of time it is possible for individuals avoiding food chemicals to build up a level of resistance by regular exposure to small amounts in a controlled way, but care must be taken, the aim being to build up a varied diet with adequate composition.
The prognosis of children diagnosed with intolerance to milk is good: patients respond to diet which excludes cow’s milk protein and the majority of patients succeed in forming tolerance.
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