26/01/2012 12:56 GMT | Updated 27/03/2012 06:12 BST

Food Allergies And Intolerance - Symptoms, Diagnosis And Treatment

Nearly a quarter of adults think food allergy or intolerance sufferers as just ‘fussy’ eaters, yet 45% of the British population are living with a food intolerance and 2% with a food allergy.

In light of Food Allergy & Intolerance Week, we’ve got the lowdown on what it means to have a food allergy, how it’s diagnosed and what treatment is available.

What Is A Food Allergy?

In the UK, around one to two people in every 100 suffer from a food allergy. If you have an allergy, it means that your body's immune system have an adverse reaction to specific proteins in food or allergen - a mostly harmless substance that causes an allergic reaction in those prone to attacks.

Normally, your body's immune system defends against potentially harmful substances, such as bacteria, viruses, and toxins. In some people, a immune response is triggered by a substance that is generally harmless, such as a specific food.

An allergic reaction happens when the body's immune system mistakes the allergen, for example nuts or shellfish, for a harmful outsider and begin to produce antibodies called immunoglobulin E (IgE) to protect it.

Although the initial process rarely has any symptoms, the next time you eat the food, the antibodies are ready to react with it. This causes your body to release chemicals, which leads to a range of physical symptoms known as an allergic reaction. Allergens aren't usually harmful and most people aren't sensitive to them.

It’s quite common that if you have one food allergy, you may also react to other foods. For instance, if you're allergic to prawns, other shellfish or crustaceans may also affect you. This is called cross-reactivity.

What Is A Food Intolerance?

A food intolerance is not the same as an allergy because the immune system isn't activated or affected. Food intolerance occurs when the body is unable to deal with a certain type of food.

This is usually because the body doesn't produce enough of the particular chemical or enzyme that's needed for digestion of that food, which is why food intolerance symptoms usually include diarrhoea, stomach upset and abdominal cramps. Food intolerance's are commonly linked to Irritable Bowel Syndrome (IBS) and Coelic Disease.

What Are The Symptoms Of A Food Allergy?

Symptoms of a food allergy usually appear around two hours after eating the offending food.

There are many different types of symptoms, from internal pains like stomach cramps, vomiting, abdominal pain and difficulty swallowing, to physical such as swollen lips, fingers and ears, patches of itchy skin and sore rashes. Some cases are mild, such as tingling in the mouth and a skin rash, but other cases can be life threatening. This is known as anaphylaxis (or anaphylaxis shock) and causes breathing difficulties and severe swelling.

How Common Are Food Allergies?

Although food allergies are becoming more common, they aren't as widespread as many people think. According to NHS Choices, a number of surveys have found that 20 to 30% of people claim to have a food allergy.

However, a Food Standards Agency (FSA) report in 2008 estimated that only 5 to 8% of children and 1 to 2% of adults have a food allergy. Some researchers believe that the figure for adults may be slightly higher, at around 3 to 4%.

This is because many people convince themselves that they have a food allergy when in fact, it has been mistaken for food intolerance's.

Food allergies, in particular peanut, milk and egg allergies, are most common in young children. Although some ‘outgrow’ the allergies as they get older, an estimated 80% of children remain allergic for the rest of their lives.

How To Get Diagnosed

According to NHS Choices, the following tests can be done to diagnose a food allergy.

Prick Tests:

A prick test, or scratch test, is often used to test a number of potential allergens at one time. The allergist tests a number of allergens on the thin skin of the forearm or the back. A positive test will show as a hive, or wheal. An inconclusive prick test will usually be followed by a more sensitive test.

RAST Tests:

The RAST, or radioallergosorbent, test is a blood test that tests for IgE antibodies. It is often used in circumstances when a skin test would be difficult to perform (for example, in a patient with severe eczema or another skin condition) or where exposing the patient to an allergen might be unnecessarily risky (for example, in cases of suspected severe peanut allergies). A positive test result indicates that the body has produced antibodies to an allergen and is primed for a reaction.

Elimination Diet:

An elimination diet can be undertaken in several ways, depending on the allergist supervising it, but the basic principle is the same: the diet begins with a limited set of foods that are deemed unlikely to cause a reaction. Other foods are added one by one over a period of days or weeks.

While the elimination diet can be tedious, it can be an effective way to determine which substances are problematic when skin testing is inconclusive. It can also help diagnose food intolerance's, which may cause problematic symptoms but will not show up on an allergy test.

Food Allergy Treatment

"We would urge those who are experiencing symptoms of a food allergy to visit their GP and ask for a referral to an allergy consultant in a specialist allergy clinic," says McManus Allergy UK.

"Most severe reactions are due to an allergic response and can be identified by the blood or skin tests in NHS clinic allergy testing. If a severe allergy is identified, it’s important the sufferer avoids even the most tiny amount of the trigger food or substance. Anyone suffering a severe allergic reaction should be given any prescribed treatment without delay, such as adrenaline by injection, antihistamines, steroids or all of these.

"We advise those who suspect food intolerance to keep a food diary for three weeks to identify the offending food. We recommend they visit their GP to discuss the results of their food diary and obtain a referral to a dietician, if their GP feels this is appropriate. Without consulting with a qualified medical professional you can run the risk of poor nutrition or eating a dangerous diet.

"However, food allergies and intolerance often go undiagnosed by GPs who do not recognise key symptoms of the condition. A dietician at your local hospital may be able to help you investigate the cause of your food intolerance."

Living With It

People with allergies have to watch what they eat and ensure that no cross-contamination takes place with foods that may contain high-risk allergens. The EU food labeling legislation was brought into action in 2005 and means that all food must clearly outline its ingredients and whether it contains an allergen, such as eggs or nuts.

"Living with food allergy or food intolerance can have a huge impact on everyday tasks such as grocery shopping, eating out at restaurants or at friends’ houses, and going away on holiday. Sufferers need to plan their means in advance whether they are eating out or going on holiday.

"It’s important they know where to find suitable alternatives to ensure they’re eating a balanced, nutritional diet. We recommend that those with food allergies or intolerance's cook using fresh ingredients as much as possible," says Lindsey McManus, Deputy CEO, Allergy UK.

"A weekly shop can take a lot longer as sufferers need to check the list of ingredients as well as allergy advice warnings (where available). Allergy UK offers a free food allergy alert service to notify sufferers if a product has been recalled due to incorrect or missing allergen information. You can also ask your local supermarket or shop for additional information on their free from range."

Eating Out - What To Avoid

According to Bupa, when eating out, those with food allergies should avoid the following dishes:

  • Malaysian, Chinese and Indian dishes - these often contain nuts or are cooked using nut oils.
  • Salads - these can be garnished with nuts or dressed with nut oils.
  • Desserts - nuts are often used as garnishes or may be present in the form of ground almonds or in the dessert base where they aren't immediately obvious.
  • Food in self-service areas - these are at risk from cross-contamination (as in non pre-packed foods).

If you think you might be allergic to a particular food and want to seek advice, visit Allergy UK or call 01322 619 898, for around the clock advice and support.

Common Allergenic Foods