Food Allergy and Food Intolerance
There are 20 million people in the UK who are suffering with an allergy at any one time; of these, the numbers who are diagnosed with a food allergy is rising faster than for any other allergy. With this in mind, STH Online went to speak to Fran Ashworth, Senior Clinical Immunology and Allergy Nurse Specialist, to find out more.
What is food allergy and food intolerance?
A food allergy is an allergic reaction to something that is eaten. Food allergy is caused when the body mistakes the proteins in food as a dangerous substance and produces antibodies to fight it, which causes a reaction to that particular food. When the food is eaten, the immune system releases chemicals such as histamines, which cause various symptoms including asthma, rashes and swellings, hay-fever, vomiting, tummy pain, and in the most severe cases can cause anaphylaxis (a severe allergic reaction causing collapse, with breathing difficulties or low blood pressure).
Food intolerance is much more common than food allergy and describes any adverse reaction to food that does not involve the immune system. Food intolerance is very unpleasant but rarely dangerous.
Food intolerance has a number of different causes and not all are known. Some reactions are a predictable result of natural substances in the food, which cause adverse symptoms if you eat a large enough dose, or if you are more susceptible to the effects for some reason, such as lacking an enzyme needed to tolerate the food (examples would be food-induced migraines or lactose intolerance). Coeliac disease is an immunological reaction to wheat gluten, but is a different type of allergy, but should be excluded in patients with symptoms related to wheat or cereals.
There are a number of foods that contain naturally occurring toxins, which also result in adverse reactions if enough of the food is eaten. Whilst chemical and food additives are often suspected as a cause, there is little evidence that symptoms of intolerance are directly due to these substances, except in a few cases, eg an excess of monosodium glutamate (a food additive).
Food intolerance often varies throughout a person's lifetime and patients can sometimes tolerate a small amount of the food in question.
What foods are affected?
Any food can cause an allergy, but there are some that are more common than others; these include milk, eggs, wheat, nuts, soybeans, peanuts, fruits, vegetables and seafood.
The most common foods which cause intolerance are milk, eggs, nuts, seafood, wheat, flour, chocolate, artificial colours, pork, bacon, chicken, tomato, soft fruit, cheese and yeast, but any food can cause an intolerance, which can appear at any time in your life.
Is food allergy and food intolerance common?
Up to 20% of the population have adverse reactions to food and most suffer food intolerance, but only approximately 1% of adults and 2-4% of children are truly food allergic.
Who is at risk?
A tendency to allergies (Atopy) often runs in families and patients are therefore at an increased risk of having a food allergy if their mother or father or a sibling has an allergy.
What are the common symptoms?
Patients suffering allergic reactions to food can experience symptoms such as abdominal pain or bloating, vomiting and diarrhoea, runny nose, sneezing, wheezing or a cough, itching, swelling or rash, body swelling, breathing difficulties, and in more extreme cases anaphylaxis. Symptoms usually occur within 20 minutes and very rarely can be delayed for a couple of hours.
Food intolerance can cause fatigue, bloating, irritable bowel, joint pains, rashes, flushing, abdominal pain, eczema, vomiting and diarrhoea, palpitations and migraine. The onset of symptoms is very variable. Symptoms can last for many hours and in some cases, well into the next day. Patients with intolerance to gluten or wheat may have coeliac disease (a different type of allergy to gluten in cereals) which will need to be excluded.
A patient suffering a food allergy will generally experience a more limited range of symptoms than patients experiencing food intolerance, who often suffer multiple symptoms at the same time.
How is food allergy and food intolerance diagnosed?
The key to diagnosis is a careful allergy history taken by an allergy specialist. Blood and skin tests are used to provide additional evidence, but are never used alone to diagnose allergy as they can be positive without allergy and vice versa.
A skin-prick test is a quick and easy way of identifying whether an antibody is present and involves introducing a small amount of the suspected food to the skin, then pricking through with a lancet or scalpel. If the patient is sensitised the skin will become itchy within a few minutes, then red and swollen.
If the skin-prick test cannot be done for any reason, a test to detect the IgE antibody in the blood can be used instead.
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