Posted 25 September 2018

Here at The London Clinic of Nutrition, we regularly receive enquires about food intolerance and allergy testing. We often try to deter patients from ordering these tests, simply because their accuracy is so variable.

Even if a patient tests positive for a particular food, it doesn’t necessarily mean that they have a problem with that food! Not only can food intolerance tests give false positives, they can also give false negative results.

This leaves the patient in a confused position when they receive their test results back—and no clearer as to what they should or shouldn’t be eating.

How do food intolerance tests work?

Food intolerance tests are generally done via a blood test. The technicians in laboratories place your blood sample on a food antigen (a food you might react to), and look to see if any immunoglobulins are present.

The easiest way to understand this is to imagine your immunoglobulins as the armed forces of your immune system. When a food intolerance test is run, they’re looking to see which armed forces come out to fight.

Most labs measure only one section of the armed forces called IgG—let’s imagine this is the army. There are other immunoglobulins such as IgE, IgA and IgM, which we can call the navy, the air force and the coast guard respectively.

When a sample of your blood is applied, the technician is only looking to see if the army has come out to fight. They’re not even considering the navy, the air force and coast guard. This means there’s a very high chance of false negative results.

Sadly, at present there’s no food intolerance test on the market that measures all the immunoglobulins (all sections of the armed forces).

Is food intolerance testing accurate?

One issue with food intolerance tests is that the antigens used tend to come from raw food. This isn’t a true reflection of how we eat.

Let’s take rice as an example. People eat rice cooked, and yet food intolerance tests will look to see if a person’s blood reacts to the raw rice antigen. Cooking changes the food’s protein structure, so even if we don’t react to the raw rice antigen, we could still react to the cooked version (which isn’t tested for). Again, this can produce a false negative result.

A further problem with food intolerance testing is that there appears to be a lack of consistency. Here at the London Clinic of Nutrition, we’ve found that when conducting parallel sampling of IgG food sensitivity panels, we receive a variation in results from samples taken from the same person on the same day.

What happens when my food sensitivity panel shows that I am sensitive to nearly all the foods on the panel?

We’ve seen this on many occasions. Patients may have been to other practitioners, and have been told to avoid all the foods that come back as ‘yellow’ or ‘red’ on a food sensitivity panel. This often leaves the patient with very little to eat.

The issue here is twofold. Firstly, if a patient is coming up ‘positive’ to a high number of foods, it often means they have a degree of intestinal permeability (leaky gut), rather than a simple intolerance to a selection of foods. Secondly, if the test is solely an IgG antibody test, it’s worth bearing in mind that IgG food reactions aren’t always a negative situation for the patient.

What’s more, there’s a large element of cross-reactivity between foods that are tested. The body can make mistakes when recognising the protein structures of particular foods: they can mistake it for another food, or even a pathogen such as a virus.

Because of this, it’s not unheard of for a patient to test positive for a food that they’ve never eaten in their life. This is because they’re cross-reacting to another food with a very similar protein structure.

What’s the best food intolerance test?

The best food intolerance test is an elimination diet—or what’s known in the medical literature as an oligoantigenic diet.

This involves removing several foods for a period of time (at least 28 days) and then reintroducing them one at a time. After each food, the patient waits three days and observes any reactions that arise.

What should I do if I think I have a food intolerance?

If you suspect you have a food intolerance, the best advice is to conduct an elimination diet as outlined above.

It’s also worth getting in touch with The London Clinic of Nutrition, as often the underlying cause of food sensitivity can be other conditions such as SIBO, intestinal permeability, low stomach acid (HCL), low digestive enzymes or an overactive stress response.

These are all conditions that we see regularly and treat successfully at the clinic. We look forward to helping you with your food choices.

For further information, please get in touch or ring us on 020 3332 0030.

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Thank you


So true, I wish I had saved my €250 that I had spent on one of those food intolerance tests (non IgG) for Christmas instead...

25 September 2018

Chrissy Wood

There is a more advanced test out there by Dunwoody Labs (through Invivo) that tests for IgG, IgG4, IgE, C3d and blocking potential.

25 September 2018


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