A Food Allergy
A food allergy ; is hypersensitivity to dietary substances, leading to various types of gastrointestinal complaints. It occurs mainly, but not exclusively, in children. It is a common type of allergy, and is usually treated with an exclusion diet. To keep the body safe from harmful germs and bacteria, the immune system produces antibodies as a way of protecting us from foreign and potentially harmful invaders. However with food allergies, a common and benign food protein can cause the body’s immune system to overact. As a result the body undergoes chemical reactions in it’s attempt to defend against the ” offending ” food. These reactions can range from mild to life threatening.
Food Intolerances occur in individuals whose bodies lack enough of an enzyme to properly digest a certain food substance. For many people, a common intolerance is for lactose – sugar found in cow’s milk. The inability of the body to break down or digest this sugar can cause side effects such as gas, bloating and abdominal pain. Although uncomfortable, food intolerances are often harmless and people with them may be able to tolerate the food that effects them if consumed in small quantities.
Signs and Symptoms
Patients present with skin symptoms, throat tightness, shortness of breath, light-headedness and/or stomach symptoms. These symptoms usually develop within half an hour of ingesting the allergen.
Rarely but more importantly, some food allergies can lead to anaphylactic shock: hypotension (low blood pressure) and loss of consciousness. This is a medical emergency. Allergens commonly associated with this type of reaction are peanuts, nuts, milk, egg and seafood’s. (Latex products can induce similar reactions).
Anaphylaxis may begin mildly enough with itching around the eyes, widespread hives, a cough and a feeling of anxiety and discomfort. Symptoms can appear in rapid succession, often within minutes of exposure to the allergen, or in some cases several hours after exposure. When some one says that they are having an anaphylactic reaction – believe them! It’s better to be safe then sorry.
Food allergy is thought to develop more easily in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, excema and asthma. The syndrome has a strong inherited component; a family history of these diseases can be indicative of the atopic syndrome.
Some symptoms to watch for:
- itching skin, lips, tongue, throat
- swelling of any body part
- runny nose/nasal obstruction
- problems swallowing
- tightness or closing of the throat
- change in skin colour or voice
- cold, clammy skin
- decreased blood pressure
- fainting or loss of consciousness
The Big Nine
The most common food allergies are:
- Tree nut
These are often referred to as “the big nine,” Corn and sesame is also common allergens. Likelihood of allergy increases with exposure. For example, rice allergy is more common in Asian nations where rice forms a large part of the diet. These most common food allergens account for about 90% of all allergic reactions.
Any food allergy has the potential to cause a fatal reactions.
The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will discuss the symptoms that occurred after the food ingestion. If the allergist feels the reaction is in keeping with a real food allergy, he/she will perform allergy skin tests.
These skin tests are performed by a method called skin prick testing, which is a somewhat uncomfortable test tolerated by most adults but not all children. The results are available within 15 minutes. Another option is to perform blood testing, called RAST testing, for the foods that are suspected as allergens. ELISA tests for IgE may also be used. Blood tests allow for hundreds of allergens to be screened from a single sample, and cover food allergies as well as inhalants.
Important differential diagnoses are:
- Lactose intolerance; this generally develops later in life but can present in young patients in
severe cases. This is due to an enzyme deficiency (lactase) and not allergy. It occurs in many
- Celiac disease; this is an autoimmune disorder triggered by specific proteins such as gliadin
(present in wheat and other grains).
- Irritable bowel syndrome (IBS); although many IBS cases might be due to food allergy, this is an important diagnosis in patients with diarrhea in whom no allergens can be identified.
- C1 esterase inhibitor deficiency (hereditary angioedema); this rare disease generally causes
attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea.
See also allergy for a general discussion of the background of allergy.
Generally, introduction of allergens through the digestive tract is thought to induce immune tolerance. In individuals who are predisposed to developing allergies (atopic syndrome), the immune system produces IgE antibodies against protein epitopes on non-pathogenic substances, including dietary components.
The IgE molecules are coated onto mast cells, which inhabit the mucosal lining of the digestive tract.Upon ingesting an allergen, the IgE reacts with its protein epitopes and release (degranulate) a number of chemicals (including histamine), which lead to oedema of the intestinal wall, loss of fluid and altered motility. The product is diarrhea.
The immune system’s eosinphils, once activated in a histamine reaction, will register any foreign proteins they see. One theory regarding the causes of food allergies focuses on proteins presented in the blood along with vaccines, which are designed to provoke an immune response.
Flu vaccines and the Yellow Fever vaccine are still egg-based. As of 1994, Measles-mumps-rubella vaccines no longer uses eggs. There is resistance to this theory, especially as it applies to autoimmune disease. Another theory focuses on whether an infant’s immune system is ready for complex proteins in a new food when it is first introduced.
The mainstay of treatment for food allergy is avoidance of the foods that have been identified as allergens.
If the food is accidentally ingested and a systemic reaction occurs, then epinephrine (best delivered in an EpiPen) should be used. Epinephrine is a form of adrenalin medication used during severe allergic reactions.
It prevents the body from releasing the chemicals that cause anaphylaxis. This should slow down or stop an allergic reaction. For those with life-threatening allergies it can be essential in saving their lives – it gives them more time to get to the hospital for assessment and further treatment if needed. It is possible that a second EpiPen dose may be required for severe reactions. The patient should seek medical care.
At once. There is no allergy desensitization or allergy “shots” available for food allergy.
For reasons that are not entirely understood, the diagnosis of food allergies has become more common in Western nations in recent times. (This trend seems to apply to asthma as well.) In the United States, it is believed that about 4% of the population suffers from food allergies. In children, this number is believed to be significantly higher.
Various medical specialties have a differing view on food allergies. What is called irritable bowel syndrome by many doctors (a stress-related functional disorder) is often interpreted by allergists to be food allergy.
In addition, many practitioners of complementary and alternative medicine ascribe symptoms to food allergy where most classically trained doctors would not find a causal relationship. Examples are headaches, tiredness and hyperactivity. Nevertheless, hypallergenenic diets can be of benefit in these conditions, indicating that the current medical views on food allergy may be too limited.
Three suggested levels of response; classical immediate-onset allergy (IgE), delayed-onset allergy (giving a positive response on an ELISA IgE test but rarely on an IgE skin prick test), and food intolerance (non-allergic), and claim the last two to be more common.
Milk and soy allergies in children can often go undiagnosed for many months, causing much worry for parents and health risks for infants and children. Many infants with milk and soy allergies can show signs of colic, blood in the stool, reflux, rashes and other harmful medical conditions.
These conditions are often misdiagnosed as viruses or colic. Many children who are allergic to cow’s milk protein also show a cross sensitivity to soy-based products. There are infant formulas in which the milk and soy proteins are degraded so when taken by an infant, their immune system does not recognize the allergens and they can safely consume the products.