Food allergy is an abnormal response of our body’s immune system which is triggered by certain food components. Our body produces a specific type of antibody called immunoglobulin E (IgE) and when IgE binds to specific molecules present in the food it triggers the immune response.
The response can be mild or in some cases it may be a severe or life-threatening reaction called anaphylaxis. In some cases, a reaction to food is not an allergy at all, but may be another type of reaction called food intolerance.
The allergic reaction process
Allergic reaction to food is a two-step process as follows:Step 1: This includes the first time exposure to a food, which act as food allergen to our immune system and specific IgE antibodies are produced against that allergen. The antibodies then circulate through the blood and are attached to mast cells and basophils. Mast cells are found in body tissues, especially in the areas which are the typical sites of allergic reactions including the nose, throat, lungs, skin and gastrointestinal (GI) tract. Step 2: This includes the repeated exposure of the same food allergen, which binds to the IgE antibodies that are attached to the mast cells and basophils. The binding signal stimulates these cells to release massive amounts of inflammatory chemicals such as histamine, which produces various symptoms of food allergy.
An allergic reaction to food usually takes place within a few minutes to several hours after eating. The process of eating and digesting food as well as the location of mast cells may both affect the timing and location of the allergic reaction.
Symptoms of food allergy
Any person allergic to a particular food may experience the following symptoms:
- Swelling of lips and tongue
- GI symptoms such as vomiting, diarrhea, abdominal cramps and pain
- Urticaria (itching)
- Aggravation of eczema
- Difficulty in breathing
- Fall in blood pressure
Food allergies generally develop in the early years of life, but can occur at any age. The common foods that cause allergic reactions in infants and children are eggs, milk, peanuts, soy, wheat, and tree nuts such as walnuts. Similarly, in adults, the common foods are peanuts, tree nuts, fish such as salmon, and shellfish such as shrimp, crayfish, lobster, and crab.
Diagnosing Food allergy
The diagnosis of a food allergy begins with the detailed medical history to find out the symptoms which are caused due to specific foods. Sometimes patients are asked to keep records or maintain a food diary that includes what the patient eats and whether the patient has a reaction.
In some cases, an elimination diet technique is employed by the healthcare professional for diagnosis in which the food that is suspected of causing an allergic reaction is removed from the diet.
When the above methods suggest a specific food allergy, then a skin prick test is employed to confirm the diagnosis. In this test, a needle is used to place a tiny amount of food extract below the skin surface of the lower arm or back. If the person is allergic, then there will be swelling or redness at the test site. Skin prick test is simple, safe and results are obtained in a few minutes.
Blood samples can also be taken to measure levels of food-specific IgE antibodies. The results of blood test or skin prick test are jointly correlated with the history of reactions to make an accurate diagnosis of the food allergy.
An oral food challenge is the final method that may be employed for the diagnosis of food allergy. This method includes giving individual doses of various foods and observing whether allergic reactions occur.
Prevention and treatment of food allergy
At present there is no cure for food allergies and one can only prevent the symptoms by avoiding the allergenic food. After identifying the food to which the patient is sensitive, it should be removed from their diet. Patients with food allergies should be instructed to read the list of ingredients on the label of prepared foods before eating to ensure the allergen is not listed.
Apart from this, patients should be prepared to treat an unintentional exposure. This can include measures such as wearing a medical alert bracelet or necklace, carrying an auto-injector device, and also carrying relevant medicines for controlling mild allergic symptoms.
Food intolerance is characterized by difficulty in digesting particular foods. Food contains proteins, vitamins, carbohydrates, fats and natural chemicals that add to its flavor and smell. Some of these can trigger symptoms of food intolerance. Food intolerance differs from food allergy, where even a small amount of the allergic food can cause a mild to severe immune response. Food intolerance usually develops gradually and may occur when you consume too much of the particular food, too often.
The symptoms caused by food intolerance include fatigue, dark circles under the eye, joint pain, night sweats, diarrhea, vomiting, bloating, irritable bowel and skin-related symptoms such as rashes and eczema.
Food intolerance is specific to you, and is caused by foods that are normally safe for a majority of others. Some of the common causes include:
- Lack of enzymes specific for the breakdown of certain foods
- Certain naturally occurring chemicals such as caffeine
- Some foods such as kidney beans or chickpeas that exert a toxic effect when undercooked
- Food containing histamines such as fish that has been stored poorly
- Salicylates in certain fruits, vegetables, herbs and spices
- Wide variety of artificial additives, preservatives and coloring agents used in processed foods
The pattern and type of symptoms help to distinguish food intolerance and differentiates it from allergic reactions. Keeping an accurate record of your food intake and resulting symptoms, helps to identify the foods that may cause these reactions.
Once the triggering food is determined, you are advised to temporarily eliminate it from your diet under controlled conditions. You are then observed for improvement or relief from symptoms. Following this, the trigger is reintroduced into your diet to confirm on the diagnosis. This is carried out under the supervision of a dietitian who will substitute the eliminated food with similar food, ensuring that nutrition is maintained.
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