Testing for Food Allergies and Intolerances
There is now an increasing number of people who identify themselves as intolerant or allergic to foods. Having an intolerance or an allergy to a food are two different things and below I’ll discuss what the difference is.
A food allergy is when the body’s immune system reacts to a specific food, thinking that the body is under threat. Any food can actually cause an allergic reaction, however there are certain foods which are more commonly the cause, including: milk; eggs; peanuts; tree nuts; fish and shellfish (NHS, 2016a).
The symptoms of a food allergy can include:
- An itching sensation inside the mouth, throat and ears
- Raised itchy red rash
- Swelling of the face, eyes, lips, tongue, and roof of mouth
Over the last 20 years the number of individuals to have food allergies has risen.
Types of Food Allergies
There are three main types of food allergies and these depend on what symptoms an individual experiences and when they occur.
IgE-mediated food allergy: this is the most common and is caused when our immune system produces an antibody called immunoglobulin E (IgE). A few seconds, or minutes after the individual has eaten the food, symptoms start to develop.
Non-IgE-mediated food allergy: this reaction isn’t caused by IgE but by other cells within our immune system. The symptoms for this takes much longer to become apparent and is harder to diagnose.
Mixed IgE and non-IgE-mediated food allergy: this is when people may experience symptoms from both types.
Testing for Food Allergies
Tests for food allergies must be carried out by a registered healthcare professional. These tests include:
- Skin prick test: this is when a small amount of the diluted allergen is placed onto the skin, and the skin is then pricked. If a small swollen lump forms an IgE mediated food allergy may be diagnosed.
- Blood test: this is a specific IgE test, which looks at the amount of IgE antibodies in the blood to the suspected food. The results also look at a detailed clinical history, to help with diagnosing a food allergy.
- Food challenges: the food in question is consumed in small amounts and the amount is built up gradually, and symptoms are observed.
- Food exclusion and reintroduction: where the food is excluded for a period of time and symptoms are observed and recorded. If they improve then the food is then reintroduced. If this causes the symptoms to reoccur, it would indicate an issue with that food.
As we’ve seen above, food allergies are an immune system response to a food, whereas a food intolerance can also be called a sensitivity and is not an immune system response.
When you have an intolerance to a food, it may be caused by a difficulty to digest certain food. This may be due to:
- Missing enzymes (e.g. lactase missing to break down lactose = lactose intolerant)
- Irritable bowel syndrome
- Reactions to naturally occurring substances
- Sensitivity to additives
- Stress or psychological factors
Your healthcare professional will be able to help you with the diagnosis of these.
With food intolerances, consuming the food causes symptoms such as bloating, stomach pain, wind, diarrhoea, and skin rashes. These symptoms usually arise a couple of hours after eating the food.
In some cases, such as for determining lactose intolerance, you will be asked to drink a solution of lactose, then blood will be taken to see how much glucose your blood contains (NHS, 2016c). They look at your glucose because if you are lactose intolerant you will not be able to break down the lactose into glucose and galactose, due to not having the enzyme.
Testing for Food Intolerances
At-Home Intolerance Testing
One of the most common ways people find out about their intolerance to a food group is through at-home testing kits. With these, you send a sample of your blood and it gets tested against numerous foods. This kind of test is called an IgG blood test, and at present there is not enough convincing evidence to support the use of this test for the diagnosis of intolerance. So, it is not recommended as a diagnostic tool (British Dietetic Association, 2017).
IgG Blood Test
What does IgG blood test look at? Our body produces IgG antibodies when we eat food, and this test looks at this present in our blood. This test claims that when IgG levels increase, it indicates that we have an intolerance to that food. However, this has not been clinically proven. A positive result to an ‘intolerance’ may just show that you have been exposed to that food - the presence of IgG simply being a normal response to the exposure of that food, and may even be a tolerance to that food, as it is a memory antibody.
The presence of IgG indicates an exposure to the food. This is a normal response for the immune system response to foreign proteins, demonstrating the immune system is functioning normally and is not, in fact, an intolerance.
The IgG antibodies change daily depending on what you have eaten. There is the concern, that if there are any false diagnosis made, that it can lead to an over restriction of foods for individuals who do not actually need to cut out some of the foods which they have been found ‘intolerant’ to.
The Canadian Society of Allergy and Clinical Immunology released a statement referringto their concern of the increasing use of IgG food intolerance testing. They also mention a concern that a person with a true IgE-mediated food allergy, who is at severe risk of an allergic reaction may not have elevated levels of the specific IgG to their allergy, and therefore may be advised to reintroduce this food (Carr et al., 2012). It has also been found that in children who start to outgrow an allergy, their IgG levels go up, and their IgE go down.
The European Academy of Allergy and Clinical Immunology, the American Academy of Allergy, Asthma & Immunology, and the Canadian Society of Allergy and Clinical Immunology all do not recommend the use of IgG testing to diagnose both food allergies and food intolerances/sensitivities.
These IgG blood tests do not diagnose you with coeliac disease, lactose intolerances, any IgE- mediated allergies, sensitivity to histamine or chemicals. Currently there is not enough supporting evidence for BDA, the European Academy of Allergy and Clinical Immunology etc. to accept this as a validated method, so if you wish to do a IgG blood test, please just take the results with a pinch of salt, as what’s shown above it doesn’t always demonstrate an intolerance.
It is important to note that the relationship between IgG tests in relation to a food intolerance is not proven, and these tests do not indicate an allergy, only the possibility of an intolerance (Allergy Insight, 2011).
Other Tests for Intolerances
There are also other tests which can be carried out, though none of these are recommended by the British Dietetic Association for diagnosing an intolerance or an allergy. These include:
- Leucocytotoxic or Cytotoxic test
- Pulse test
- Electrodermal (Vega) test
- Hair analysis
What Recommended Tests Can Be done for an Intolerance?
There are currently not many evidence-based tests that you can do to work out most food intolerance. The NHS recommend that you monitor your symptoms and the food that you eat. You can then cut this food out of your diet for a while, and then reintroduce it back in with the assistance of a health care professional.
Whenever you believe that you have an intolerance, always go and talk to your GP as they can help determine a diagnosis and how to manage it. Take a food diary with you, write down your symptoms, so that when you go you have everything noted.
One of the best ways to monitor is through a food diary. Keep a note on what foods you are eating, and what time, and then any symptoms you have after eating these foods, and also when they come on (straight after, an hour after etc.).
Once you have identified food groups which may be causing your symptoms, you can experiment with excluding one at a time, and see if this has any impact on your symptoms. It is recommended by the NHS if cutting out a food, removing it for 2-6 weeks and see if your symptoms get better, then try reintroducing the food in small amounts, and see whether the symptoms come back (NHS, 2016b).
You can then also work out how much and how often you can consume that food. If you are planning on doing an elimination diet, it is best to speak to your GP, dietician or registered nutritionist to make sure that you are still getting all the nutrients needed. Or, you should always ensure that you are aware of what cutting out the food may impact, in regard to nutrients.
You should never restrict your child’s diet unless you have been advised to do so by a dietician or a doctor. If you are concerned about an intolerance, speak to your GP or a dietician before cutting out food groups as this can lead to malnutrition and stunted growth.
If you think you have an allergy to a food, write down the foods that you have eaten and what symptoms you experience and go talk to your GP about it. They will be able to point you in the right direction to get help.
If you are going to do an intolerance test, do some research around it and just remember that it is currently not a recommended tool by the NHS to diagnose an intolerance as it does not have enough evidence behind it. Just remember that these results are not a definite positive for an intolerance and it could just be your body’s immune system responding to the proteins. These tests can lead to restrictive eating, and the restriction from having a healthy diet. If individuals are unaware that the results do not truly indicate an intolerance, this in itself can be very harmful. Restrictive eating can also lead to nutrient deficiencies, which can in turn lead to a wide variety of health problems to our body.
If you are cutting out food groups, you need to consider how they may impact your diet, such as dairy, which is a source of calcium. If you cut this out but do not consider your other sources of calcium it can impact your risk of osteoporosis and your bone health. Before you do this on your own, carry out a food dairy, detailing the foods you have eaten, the time and symptoms you experience, just after, 1 hour, 2 hours, 3 hours etc. When you carry this out for a duration of time, this may help you to identify suspect foods, in which case you can then carry out exclusion and reintroduction of foods. Again, if you do not feel comfortable carrying this out on your own, talk to your GP and they will be able to assist you.
If you are frequently experiencing problems, especially gastrointestinal, talk to your GP as it may not be an intolerance, but another condition which may cause similar symptoms.
It is important to also note that coeliac disease is an autoimmune disease and cannot be tested from at-home kits. Coeliac disease is a reaction of the immune system to gluten. When consumed, the immune system responds by attack and damaging the lining of the small intestine. This then causes malnutrition, and other complications due to the small intestines not being able to absorb nutrients (Coeliac UK, 2018a).
If you think you have coeliac disease and have symptoms that point towards it, as with everything above, you need to speak to your GP. If your GP thinks that you have coeliac disease, they will be able to do a blood test to check for antibodies. It's important to note that when you are being tested, you must keep eating gluten throughout the process, until diagnosis. This is due to the test looks at how the body responds to gluten and if you cut or reduce when being tested, chances are you will receive an inaccurate result (Coeliac UK, 2018b).
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Daisy, MSc PGDip ANutr, is a Registered Associate Nutritionist with a Master's Degree in Public Health Nutrition, and a Post Graduate Diploma in Eating Disorders and Clinical Nutrition, both of which are Association for Nutrition (AFN) accredited. She, also, has a BSc degree in Psychology and Cognitive Neuroscience; and has completed an AFN accredited Diet Specialist Nutrition course.
Daisy has worked for an NHS funded project, the Diabetes Prevention Programme; and shadowed a nutritionist in Harley Street.
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Allergy Insight. (2011). NICE, Allergy UK, Food Allergies, and Unproven Allergy Tests. Available here.
British Dietetic Association. (2017). Food Allergy and Intolerance. Available here.
Carr et al., (2012). CSACI Position Statement on the Testing of Food-Specific IgG. Available here.
Coeliac UK. (2018a). Causes. Available here.
Coeliac UK. (2018b). Getting Diagnosed. Available here.
NHS. (2016a). Food Allergy. Available here.
NHS. (2016b). Food Intolerance. Available here.
NHS. (2016c). Lactose Intolerance. Available here.