Soy allergy is a type of food allergy. It is a hypersensitivity to ingesting compounds in soy (Glycine max), causing an overreaction of the immune system, typically with physical symptoms, such as gastrointestinal discomfort, respiratory distress, or a skin reaction. Soy is among the eight most common foods inducing allergic reactions in children and adults. It has a prevalence of about 0.3% in the general population. Soy allergy is usually treated with an exclusion diet and vigilant avoidance of foods that may contain soy ingredients. The most severe food allergy reaction is anaphylaxis, which is a medical emergency requiring immediate attention and treatment with epinephrine.
Signs and symptoms
Acute soy allergy can have fast onset (from seconds to one hour) or slow onset (from hours to several days), depending on the conditions of exposure, whereas long-term soy allergy may begin in infancy with reaction to soy-based infant formula. Although most children outgrow soy allergy, some may have the allergy persist into adulthood.
IgE allergy Symptoms may include: rash, hives, itching of the mouth, lips, tongue, throat, eyes, skin, or other areas, swelling of lips, tongue, eyelids, or the whole face, difficulty swallowing, runny or congested nose, hoarse voice, wheezing, shortness of breath, diarrhea, abdominal pain, lightheadedness, fainting, nausea and vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated by wheezing, a blocked airway and cyanosis, the latter by weak pulse, pale skin, and fainting. When such severe symptoms occur, the allergic reaction is called anaphylaxis. Anaphylaxis occurs when IgE antibodies are released into the systemic circulation in response to the allergen, affecting multiple organs with severe symptoms. Untreated, the anaphylactic response can proceed to a rapid heart beat, systemic vasodilation and a rapid decrease in blood pressure as conditions of anaphylactic shock, requiring emergency intervention to prevent a fatality (rare for soy allergy).
Non-IgE allergy Non-IgE mediated allergic reactions are slower to appear, and tend to manifest as gastrointestinal symptoms, without cutaneous or respiratory symptoms. Within non-IgE reactions, clinicians distinguish among:
food protein-induced enterocolitis syndrome (FPIES) food protein-induced allergic proctocolitis (FPIAP) food protein-induced enteropathy (FPE) The most common trigger-foods for these types of reaction are cow's milk and soy. FPIAP is considered to be at the milder end of the spectrum, and is characterized by intermittent bloody stools. FPE is identified by chronic diarrhea which resolves when the allergenic food is removed from the individual's diet. FPIES can be severe, even leading to anaphylaxis characterized by persistent vomiting 1–4 hours after an allergen-containing food, to the point of lethargy. Other symptoms may include headache and abdominal swelling (distension). Watery and sometimes bloody diarrhea can develop 5–10 hours after the triggering meal, to the point of dehydration and low blood pressure. Infants reacting to soy formula may also react to cow's milk formula. International consensus guidelines have been established for the diagnosis and treatment of FPIES.
Mechanisms
Allergic reactions are hyperactive responses of the immune system to substances that are normal components of foods, such as proteins. Food protein allergens are detected by allergen-specific immune cells which produce reactions and characteristic symptoms primarily when raw foods are eaten, and even after they have been cooked or digested. Conditions caused by food allergies are classified into three groups according to the mechanism of the allergic response:
IgE-mediated (classic) – the most common type, manifesting acute changes that occur shortly after eating, and may progress to anaphylaxis Non-IgE mediated – characterized by an immune response not involving immunoglobulin E; may occur hours to days after eating, complicating diagnosis IgE and non-IgE-mediated – a hybrid of the above two types In the early stages of an acute IgE-mediated allergic reaction, lymphocytes previously sensitized to a specific protein or protein fraction react by quickly producing a particular type of antibody known as secreted IgE (sIgE), which circulates in the blood and binds to IgE-specific receptors on the surface of other kinds of immune cells called mast cells and basophils. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators into the surrounding tissue causing effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth-muscle contraction. This results in runny nose, itchiness, shortness of breath, and potentially anaphylaxis. Depending on the individual, the allergen, and the mode of introduction, the symptoms can be system-wide (general anaphylaxis), or localized to the respiratory system (asthma) or skin (eczema). After the chemical mediators of the acute response subside, typically 2–24 hours after the original reaction, late-phase responses referred to as non-IgE mediated can occur due to the migration of other types of white blood cells to the initial reaction sites, causing diarrhea and other signs of gastrointestinal upset. Allergenic proteins from soy are named under a nomenclature decided by IUIS, which is also responsible for numbering many of the proteins. Proteins numbered by IUIS include:
Gly m 1, a hydrophobic protein Gly m 2, defensin Gly m 3, profilin Gly m 4, PR-10 Gly m 5, vicilin, a cupin Gly m 6, legumin, a cupin Gly m 7, seed biotinylated protein Gly m 8, 2S albumin These proteins are recognized by the immune system as antigens in susceptible individuals. As many as 8 other soy allergenic proteins are known.
Diagnosis
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