4th February 20

Working as a dietitian I get many patients ask me about allergies and intolerance’s, specifically around allergy testing.

There are many companies and individuals who claim to diagnose people with allergies and intolerance’s, but how do you know which is legitimate and which are just looking for a quick buck?

What is an allergy?

An allergy is caused by an immune response to a specific substance which is not typically harmful to your body. In food allergies, the substance is a protein in a food, e.g. cow’s milk, egg, peanut, soya etc.

What is an intolerance?

An intolerance is known as a ‘non-allergic food hypersensitivity’. This does not involve the immune system and is caused by inefficiency in digesting a sugar in food, as seen in lactose intolerance.

How can we test for allergies?

Testing for an allergy depends on the type of allergy you are suspecting. There are two types of allergy –

IgE mediated food allergies – causes immediate reactions e.g. lips swelling, hives, anaphylaxis

Non-IgE mediated food allergies – causes more delayed reactions and slower onset, such as constipation/ loose stools, reflux and eczema.

Testing for an IgE mediated food allergy can be done using a blood test for the specific IgE antibody of the suspected food allergy or using a skin prick test. This is usually carried out by a trained health professional.

Results to these types of tests tell you whether you are “sensitised” to the food and not whether you are “allergic” to the food. It is not used solely as a diagnostic tool because you can get a “false positive” (you have no symptoms when you eat the food but test result is positive) or a “false negative” (negative result when you actually have symptoms every time you eat the food). This is important to remember and the reason why we do not carry out food tests for every food on the planet! We use clinical history to guide our judgment about which foods are suspected and should be tested for. We do not want you to be avoiding food unnecessarily.

Testing for a non-IgE food allergy is a bit more complicated. This is because the reaction is a cell mediated response, so there are no specific markers we can look for in the blood. This means there is currently no clinically verified test to look for this. The “gold standard” approach, as recommended by the National Institute for Health and Care Excellence (NICE) is to remove the suspected food from the diet for 2-4 weeks. After this exclusion period, you then reintroduce the food back into the diet, and you should see reproducible symptoms each time the food is introduced. If you do not get the same symptoms with the reintroduction, you are not allergic to the food (hooray!). If you do have the same symptoms on reintroduction, then you can work with a Registered Dietitian who is competent in allergy, to monitor and potentially desensitise you to the food. This type of allergy is often confused with an intolerance as the symptoms are usually not as severe as an IgE mediated reaction – but it is an allergy and involves an immune response!

So, what are intolerance’s?

Intolerance’s do not involve an immune response. In the case of lactose intolerance (the most common type of intolerance), it is caused by the sugar in milk (lactose) not being digested effectively by the enzyme (lactase) in the small intestine. Because the sugar is undigested it moves into the large intestine, which causes your gut bacteria to feast on it instead. This then causes wind and bloating (specifically Hydrogen gas is released from your gut bacteria) and water is drawn into your bowel which causes loose stools.

Lactose intolerance is very rarely seen in babies – they are designed to drink breastmilk and the sugar in breastmilk is lactose! The incidents of lactose intolerance in adults varies depending on ethnicity due to genetics reducing the amount of lactase enzyme produced.

Lactose intolerance can also be caused by severe gastroenteritis whereby the gut is damaged by inflammation during this time. This is usually restored after you are recovered, however sometimes an exclusion period is needed to give your gut a break to get back to normal. You can usually tolerate lactose after this time.

Similarly, lactose intolerance can be secondary to coeliac disease, again due to inflammation in the gut. This again should improve once you are on a strict gluten free diet to treat the coeliac disease as the gut will heal again.

So, as you can see there are many different mechanisms which cause allergies and intolerance’s.

There are many allergy tests out there such as IgG blood tests, kinesiology, hair analysis and electrodermal (vega) testing. Unfortunately, none of these tests are clinically validated or have any scientific research backing them for testing of an allergy or intolerance. I, therefore, would not recommend paying for these tests, as you may end up avoiding food and spending money unnecessarily. Children should also not be following a restricted diet unless they are supervised by a Registered Dietitian. This will ensure they have a well-balanced diet and are meeting their growth and developmental milestones.

Useful links:

British Dietetic Association, Food Allergy Testing

Allergy UK, Types of Food Allergy