This blog is written by our clinicians and aims to keep patients informed with up to date information on medical conditions.
Food Allergy and Food Intolerance are very hot topics.
These are widely discussed in newspapers, magazines as well as scientific journals. One of the reasons for that is the fact that food allergies and intolerances are on the rise, and we are fairly certain you know someone who has an allergy or intolerance to food, or you may even suspect you have one yourself!
It is a well-known fact that food can trigger many different types of reactions in the body:
- On the skin (such as hives, rashes, itchiness);
- In the intestines (feeling sick, abdominal pains, feeling ‘windy, diarrhoea and/or constipation);
- In the chest (such as discomfort/palpitations and fast breathing) or through generally feeling unwell or not right.
Symptoms can be severe and even cause a life-threatening anaphylaxis. It is estimated that up to 10% of children and 5% of adults have food allergies in the UK. Also 35% of children who have moderate to significant eczema will have a food allergy.
The reason why people develop such symptoms is because our immune system has the ability to mistakenly recognises certain food substances as ‘foreign’, and therefore the whole immune system can get ‘activated’which results in the production of antibodies (IgE) that trigger reactions described above. This is what typically happens in an IgE mediated food reaction.
The Ig E non-mediated reactions, such as intolerances are not as well documented. These are often dose related, meaning an individual has a tolerance level over which symptoms develop.
Why do more and more people develop food allergies?
Scientists established that certain factors like the age of weaning the babies, high rate of Caesarian sections, low vitamin D (especially during first year of life) as well as widespread antibiotic use and high levels of urbanisation and obesity are all fundamental contributors to that.
Some people tolerate their symptoms for many years, absolutely unnecessary, not realising that they could get better if the foods triggering these symptoms were eliminated from the diet.
The most common foods causing allergies are:
- Some fruits can also cause an allergy- e.g apples and some stone fruits (plums, cherries) are the most common offenders.
Finding out which foods are causing the symptoms can be straightforward for some patients and incredibly difficult for others. This is because diagnosing food allergies can be as complicated as the medical condition itself — symptoms can vary from patient to patient, and a single individual may not always experience the same symptoms during a reaction.
Cross-reactivity and Oral Allergy Syndrome
A cross-reactivity happens when antibodies against one allergen identifies other allergens as the same and therefore produce an allergic reaction. Commonly this happens with pollens and foods.
For example an individual who is allergic to birch pollen may develop symptoms when eating apples. Symptoms may consist of:
- Redness of the mouth
This is called an Oral Allergy Syndrome or OAS.
Amongst other cross-reactors are:
- Housedust mites and Crustaceans
- Hazel pollen and nuts
- Birch pollen and raw potatoes, celery, carrot, pears, hazelnuts, kiwi
- Grass pollen and kiwi, melon
- Mugworth and raw carrot, celery , aniseed and curry
- Ragweed and melon and bananas
This is a very short list and the possibilities of cross-reactivity are numerous. This cross-reactivity is important to consider when allergen identification through diagnostic tests takes place.
Food intolerance should not be confused with food allergy.
The symptoms of food intolerance can vary and may often come few hours or even days after eating an offending substance. Eating larger amounts of a specific food usually triggers the symptoms versus an allergy when the smallest amount is enough to trigger a reaction.
Commonly reported symptoms in a food intolerance are:
- Excess wind
- Frequent infections
- Muscle aches
- Water retention
- Rashes and itching.
Symptoms are usually much less severe than what you would experience with a true food allergy. It is essential to understand that our immune system is not activated in this case, and therefore food intolerances can sometimes be a challenge to diagnose correctly.
A good example to mention would be lactose intolerance. This happens when one’s small intestine stops producing as enzyme called lactase that breaks down the sugar—lactose.
It is considered to be one of the commonest types of intolerances, and frequently we see patients trying to exclude milk and other forms of dairy from their diets (often absolutely unnecessary), thus depriving themselves of important vitamins and minerals. This is where a correct diagnosis is essential so that appropriate measures are decided upon and implemented.
When a food allergy or intolerance is suspected, it is important to be seen by a trained professional who can take a detailed history, perform an examination and then order tests as deemed appropriate. Once a correct diagnosis is made counseling on food allergy management takes place.
There are many non-medical clinics and health centres on high street offering ‘allergy testing’; as are nutritionists and alternative therapists providing such services, often without having the necessary training or expertise. As the results of the tests can often be very confusing and some positive results may not actually be significant, we often see patients coming back to us asking to interpret the results of such tests for them correctly, as the last thing one wants is to start excluding foods from the diet she/he is not really allergic to!
A good medical history is the most important. Positive tests are of no value without a clinical history.
For IgE mediated reactions skin tests and/ or blood tests for serum specific IgE are the investigations of choice.
Skin tests may be:
- Skin Prick Tests – this are reproducible, sensitive, not irritant;
- Skin Prick-Prick Tests – these use raw or cooked food and are highly recommended for fruits and vegetables.
Skin tests have the advantage of more or less immediate results.
A Skin test has a negative predictive value over 95%. This means that a negative skin test results essentially confirm the absence of IgE-mediated reactions.
In general, negative skin prick test results are extremely useful for excluding IgE-mediated food allergies, but positive skin test results are only suggestive of presence of clinical food allergies.
Blood tests for specific IgEs have the advantage of obtaining multiple results with one sample, although several days later.
A positive result indicates presence of IgE not clinical reactivity.
A negative blood test essentially excludes an IgE antibody mediated reaction.
What about the Non-IgE mediated reactions, including Food Intolerances?
Like with any other food reaction, a good history, a diet history with detailed information on reactions and dietary exclusions is key.
Available on the market are IgG blood tests and food allergen cellular tests that measure an inflammatory marker produced in both Ig E and non-IgE mediated reactions.
Neither is recommended as a diagnostic test at present, due to insufficient evidence.
Treatments in Food Allergy and Food Intolerance
The key when managing a food reaction is making a correct diagnosis with a trained doctor.
Treatment of immediate / anaphylaxis reactions should be discussed and available to patients.
Food elimination should commence as indicated by a doctor and a dietician or nutritionist should be at hand. If symptoms do not resolve with dietary elimination, food may be reintroduced.
Of note is that restricting foods may leads to vitamin and mineral deficiency, hence is paramount to have the correct diagnosis.
Dietary Elimination presents issues in itself due to several factors such as:
- Hidden ingredients
- Labelling issues
- Cross contamination (shared equipment)
- “Code words” (“Natural flavor” may be cow’s milk)
If you would like to make an appointment to see one of our doctors for a food allergy/ intolerance assessment please click here. Along our doctors, expert nutritional and dietetic advice is at hand to provide you with the support you will need.