Most hypersensitive physical reactions upon food intake are caused by food intolerance and much more rarely by food allergy. Food allergy is a type of food hypersensitivity that is caused by an abnormal immune response to food proteins. These food proteins are called allergens.
Food allergy is increasing in the westernised world and affects 4% (adults) to 8% (children) of the whole population. However, it is unclear if this increase is only due to more thorough testing or a real increase of food allergy frequency. Food allergy is more common in children than in adults and boys are more often affected than girls.
These eight foods account for 90 percent of all food allergies:
- Fish (e.g., bass, flounder, cod)
- Sea food (e.g., crab, lobster, shrimp)
- Different nuts
- Tree nuts (e.g., almonds, walnuts, pecans)
Symptoms of food allergy
Signs and symptoms of food allergy can vary greatly between different types of allergens and people. They might range from mild to severe and can affect gastrointestinal tract, the respiratory tract, or the skin. General symptoms upon allergic reactions towards food are fatigue, headache or migraine, nausea, and vomiting. Often, these general symptoms of food allergy are accompanied by itchiness of the skin and/or mucosa, or swelling of the tongue.
Usually, symptoms of food allergy develop within minutes to several hours of exposure to the antigen contained in the food. In severe cases, the abnormal immune response can lead to a life threatening anaphylactic shock.
Common symptoms of food allergy
- Organ systems
- Gastrointestinal tract
- Respiratory tract
- General symptoms
- headache or migrai
- itchiness of the skin and/or mucosa
- swelling of the tongue
- Anaphylactic reactions
- If untreated, these reactions can lead to a life threatening anaphylactic shock
Because physical health, social health and mental health are influencing each other, be aware that these physical symptoms of food allergy may have a strong impact on our mental wellbeing as well.
Causes of food allergy
Food allergy is caused by an abnormal immune response to food proteins. These food proteins are called allergens. Signs and symptoms of food allergy usually present within a short period of time (a few minutes to a few hours) after eating food containing the allergen. Food allergy is caused by an abnormal immune response to an allergen that is mostly contained in one specific (type of) food. The immune system misjudges this antigen as a threat, although it is harmless to the body.
Early immune response
In the course of this (mis-)response of the allergic immune system, histamine is released and a type-I hypersensitivity reaction is stimulated, leading to the production of Immunoglobulin E (IgE) antibodies. IgE antibodies are usually used by our body to fight parasitic infections. The IgE response – also known as acute response – occurs within a few minutes to a few hours after food consumption and induces an inflammation. The IgE-response is therefore also called early immune response.
Late immune response
Apart from this IgE reaction there are also other, non-IgE mediated, immune responses occurring. These non-IgE mediated immune responses are also caused by the release of histamine and lead to a late immune response, which results from the migration of other leukocytes and macrophages to the initial site of inflammation. This late immune response is usually following 2–24 hours after the early immune response.
Risk factors for food allergy include a family history of allergies, vitamin D deficiency, obesity, and high levels of cleanliness.
Treatment of food allergy
There are four general lines of treatment for food allergies
- Food exclusion diet
However, these are treatment options that only treat the symptoms. That means these treatment options require lifelong compliance and cannot lead to a cure. The only causative treatment for allergies is oral allergen immunotherapy, which is discussed below as well.
Food exclusion diet
The main treatment option for patients with food allergy is to stick to a strict food exclusion diet. In contrast to the elimination diet – which is a diagnostic tool – food exclusion diet is an important treatment option for patients with food allergy.
Exclusion diet means total avoidance of the foods containing identified allergens. On an exclusion diet, symptoms should improve or even resolve completely, within days to weeks. Improvement of food allergy symptoms usually occurs within 2 to 4 weeks.
“On an exclusion diet, symptoms should improve or even resolve completely”
A strict food exclusion diet can be VERY challenging. As long as you are cooking for yourself you might succeed in entirely avoiding the allergen you are allergic to. But there are some food allergies that involve allergens, which are found in traces in processed foods. I am not talking only about ready-made meals and fast-foods, but also processed foods like mayonnaise or mustard.
“Whatever you use for meals and cooking, you need to read food labels”
That means whatever you use for meals and cooking, you need to read food labels! People with an allergy against wheat, nuts, or milk are especially prone to find traces of allergens in a range of processed foods.
The main problem arises when you don´t have time to cook for yourself, are invited to eat with friends or simply like to eat in a restaurant. Same applies to entirely processed foods, like ready-made meals or fast foods. It is also problematic if you simply don´t have the time to cook for yourself, because you have to work or you are busy doing things.
If you want to know more about food exclusion diet, read more here
Luckily, there are some symptomatic treatment options for food allergy, namely antihistamines and steroids. The only real treatment option is to do an allergen immunotherapy and desensitise your immune system. These treatment options are discussed below.
If you are only experiencing mild symptoms of food allergy, antihistamines might greatly improve your quality of life, especially if you want to eat out. And EVERYONE should be able to eat out sometimes.
“Antihistamines might greatly improve your quality of life”
Antihistamines block the action of histamine, which is involved in the first step of the abnormal immune response to an allergen. This accounts for both the early and the late immune response. The most common antihistamine used to improve food allergies are diphenhydramine (Benadryl) and desloratadine (Clarinex). Antihistamines can reduce mild symptoms of food allergy. However, they are inefficient in treating symptoms of anaphylaxis.
“Antihistamines block the action of histamine, which is involved
in the abnormal immune response to an allergen”
If you are experiencing severe symptoms of food allergy, corticosteroids might be the only way to achieve a decent quality of life. Severe allergic reactions (anaphylaxis) occur especially for food allergies to peanuts and tree nuts.
“Corticosteroids reduce the activity of the
immune system and improve allergic reactions”
Corticosteroids decrease inflammation and reduce the activity of the immune system, thereby greatly improving allergic reactions. However, they must be taken regularly, often daily, and have a long list of side effects (see below). If they must be taken, they are usually taken all the time and long- term side effects can occur. Also, it takes one to two weeks until corticosteroids start working. For these reasons, corticosteroids are only subscribed to patients with severe allergic symptoms. For food allergies, corticosteroids are usually taken as pills.
Early side effects
- Weight gain – due to increased appetite
- Water retention – swelling of the whole body, swollen face
- High blood pressure
- Increased growth of body hair
- Increased susceptibility to infections (viral and bacterial)
Long-term side effects
- Blurred vision
- Cataract and glaucoma of the eyes
- Muscle weakness
Epinephrine (adrenaline) is used to treat severe allergic reactions (anaphylaxis) that are occurring suddenly. Epinephrine is used to prevent the occurrence of a life threatening anaphylactic shock. There are so called epinephrine autoinjectors available, portable single-dose epinephrine-dispensing devices for intravenous injection in emergency situations.
Oral allergen immunotherapy
Allergen immunotherapy is the only treatment option that not only treats the symptoms but also the causes of allergies. For food allergies, mainly oral immunotherapy is used.
“Allergen immunotherapy is
the only causative treatment option for allergies”
The principle of desensitisation
Allergen immunotherapy is also called desensitisation or hypo-sensitisation. The principle of allergen immunotherapy is to desensitise the immune system by introducing very low doses of the allergen. Afterwards, increasing doses of allergen are administered.
“Allergen immunotherapy is also called
desensitisation or hypo-sensitisation”
In the course of a successful desensitisation the (mis-)response of the allergic immune system decreases and allergy improves.
During allergen immunotherapy, adverse systemic reactions are uncommon. However, because of the risk of severe allergic reactions (anaphylaxis) allergen immunotherapy should only be administered by trained healthcare providers and emergency medications and equipment should be immediately available.
Allergen immunotherapy in clinical practice
There are three types of administering the allergen:
- Subcutaneous immunotherapy
- Sublingual immunotherapy
- Oral immunotherapy
Beside sublingual immunotherapy, oral immunotherapy is the only causative treatment for food allergies. Protocols for oral immunotherapy vary considerably. They typically include an initial rapid dose escalation day, followed by a build-up phase, and then a maintenance phase, similar to inhalant subcutaneous immunotherapy. It seems that for patients with extreme food allergy, a slower, more cautious version of the treatment protocol is needed. Treatment efficacy is tested using oral food challenges or skin-prick tests.
If you want to know more about allergen immunotherapy, read more here
Diagnosis of food allergy
Diagnosis of food allergy is usually based on a combination of different diagnosis, carried out by a qualified healthcare provider. This can be a competent physician, doctor or another medical practitioner. The diagnosis usually involves physical investigation and laboratory tests.
- Medical history
- Skin-prick testing – only for IgE-mediated allergic reactions
- Blood test for food-specific IgE antibodies – only for IgE-mediated allergic reactions
- Food elimination diet – for IgE-mediated and non-IgE mediated allergic reactions
- Oral food challenges – for IgE-mediated and non-IgE mediated allergic reactions
- Endoscopy, colonoscopy, and biopsy – for more serious cases or if in doubt
For skin-prick tests, standardised extracts of foods containing allergens are used to test if there is an allergic reaction. When the skin is pierced the allergen can come into contact with the cells of the immune system. If there is a positive allergic reaction a hive (urticaria) occurs.
“The skin-prick test only works for IgE-mediated allergic reactions”
The skin-prick test only works for IgE-mediated allergic reactions of the early response type. Non-IgE-mediated, late response allergies cannot be detected by this test. However, a positive skin-prick test cannot predict if an allergic reaction to food containing a particular allergen will actually take place in the patient after eating this food. Therefore, food elimination diet and oral food challenges are needed.
As the skin-prick test, a blood test only detects IgE-mediated allergic reactions. In a blood test the amount of IgE-antibodies in the blood is measured. This type of IgE-measurement is only relative and needs to be compared to blood from a non-allergic person. If there is more IgE-antibody bound to a certain food than it is bound from blood from a non-allergic person, there is a great chance the patient is allergic to this food.
“A blood test can only detect IgE-mediated allergic reactions”
Advantages of the blood test are, that it causes no distress to the patient and that more allergens can be tested than with the skin-prick test. As with the skin-prick test, also the blood test cannot predict if an allergic reaction to food containing a particular allergen will actually take place in the patient after eating this food. Therefore, food elimination diet and oral food challenges are needed.
Food elimination diet
A good test if there is a hypersensitivity to a certain food is the elimination diet. It works for both, IgE-mediated allergic reactions of the early response type and non-IgE-mediated, late immune response allergies. However, food elimination diet cannot discriminate between food intolerance and food allergy.
“Elimination diet is a test for both,
IgE-mediated and non-IgE-mediated, allergies”
The food in question is withdrawn from the diet for two to six weeks. When signs and symptoms of hypersensitivity improve, this is highly indicative for a food hypersensitivity to this food. Inversely, if there is no improvement of signs and symptoms of hypersensitivity within a 2 to 4 week period, food hypersensitivity – either food allergy or food intolerance – is unlikely. In the case of an improvement upon food elimination, the food can be reintroduced and symptoms of food hypersensitivity should return.
If the food elimination diet is successful, you will definitely benefit from a food exclusion diet which can greatly improve your food allergy symptoms.
As with elimination diets, food challenges cannot discriminate between food intolerance and food allergy. A food challenge only makes sense if symptoms of food hypersensitivity have improved significantly for at least five days on elimination diet and after a minimum period of two weeks.
For a food challenge, purified food chemicals (containing the allergen) are given to the patient in the form of a pill. If signs and symptoms of food hypersensitivity are seen in the patient, this is highly indicative for a food hypersensitivity to this food.
The caveat with food challenges is that if the patient is allergic to the food this might lead to anaphylactic reactions. Anaphylactic reactions can result in a life threatening anaphylactic shock. Therefore, food challenges must be performed under careful supervision of a competent healthcare provider who is able to treat anaphylaxis immediately. Especially patients with a history anaphylaxis, asthma, or other allergies should therefore be hospitalised during a food challenge.
“Food challenges are the best way to test for both,
IgE-mediated and non-IgE-mediated, allergies”
Food challenges are the best way to detected non-IgE-mediated, late immune response food allergies. They can also detect IgE-mediated allergic reactions of the early response type.
Food challenges be carried out as double-blind, placebo-controlled food challenges (DBFCFC), allowing the highest reliability of all test methods described here. Food challenges are best interpreted in connection with a blood test or a skin-prick test.
Endoscopy, colonoscopy, and biopsy
Endoscopy, colonoscopy, and biopsy are important physical diagnostic tools for the detection of non-IgE mediated allergic reactions of the late response type. They are usually used in connection with a positive food challenge or a positive food elimination diet.