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How Does A Food Sensitivity Test Work? What Can The Test Tell You?

A food sensitivity is an abnormal reaction by our digestive systems to food or drink. They can be triggered by a whole food – for example, apple or apricot – or by a single substance within the food, such as fructose, a simple but potent fruit and plant sugar.

Food sensitivities have different causes.

These include:

  • Genetic – i.e. the absence of a substance needed to properly digest a food. An excellent example is lactose intolerance. In order to properly digest the milk sugar lactose, the body requires an enzyme called lactase, but in many people, production ceases after early childhood.
  • A digestive abnormality. Fructose malabsorption, for example, results from low levels of a molecule used to absorb fructose, causing this sugar to accumulate in the intestine. Learn more about the different types of sugars.
  • The overgrowth of gut flora, which can follow surgery, the overuse of some medications, stress or diet.

Commonest food sensitivity symptoms include:

  • Gas and bloating
  • Diarrhoea
  • Constipation
  • Stomach cramps
  • Headaches
  • Nasal congestion
  • Rashes
  • Heartburn

Food sensitivities are distinct from food allergies, although many of the symptoms are similar. Food allergies occur when the immune system misfires and responds to certain foods as though they were pathogens. Typically the symptoms of food allergies are more severe than those caused by sensitivities.


What is a food sensitivity test and how does it work?


It’s not always easy to be sure that you have a food sensitivity – or to establish which food you may be reacting to if you do have one. The symptoms often occur soon after eating a particular food – but there may be a delay of hours, even days.

And how exactly do you work out which food in a meal you may be reacting to? You may have noticed a clear link between one food and the onset of symptoms over a number of years – but many people struggle to make such connections.

Food sensitivity tests are designed to establish exactly which foods are causing problems and which are not. A variety of tests are available, but the two most widely used are:

  • Hydrogen breath tests
  • Food sensitivity blood tests


What sensitivities can they alert you to?


As the name suggests, hydrogen breath tests are used to detect the presence of hydrogen in a person’s breath. Raised levels of hydrogen are a sign of poor digestion. This test can be used to indicate fructose or lactose intolerance. They work by comparing your breath before and after consuming a drink containing one of the two substances.

A different type of food sensitivity test works by detecting the activity of immunoglobulin G (IgG), the commonest type of human antibody. These may begin to react to certain foods, triggering inflammation and uncomfortable symptoms. This is a broad spectrum assessment, designed to detect an antibody response to the many foods and spices that have been associated with digestive problems. These types of reaction are sometimes called ‘food sensitivities’, to differentiate them from intolerances, which do not involve an IgG response. Lactose intolerance does not, for example, and so will not produce a positive result with IgG tests.

The elimination diet is a third approach to this issue. Food types suspected of causing a reaction are removed from the patient’s diet and then gradually reintroduced one by one, with the return of any symptoms carefully monitored.Are food sensitivity tests reliable?

It may sound contradictory to test for an immune response when, unlike food allergies, food sensitivities do not involve the immune system. But the principle is compelling. A so-called ‘leaky gut’ is one in which the normally impermeable inner lining of the intestines develops gaps or holes. These may be caused by an unhealthy diet, excessive alcohol or painkiller use, or simply stress. The gaps may allow larger, undigested molecules of food to leak through and the body responds to these as though they were germs, triggering the release of antibodies.


How to find out whether you have any food sensitivities


If you suspect you may have one or more food sensitivities, it is important to identify the culprit foods as soon as you can and adjust your diet accordingly.

An inexpensive, home use food intolerance or food sensitivity test is a quick and easy way to do so. Following a painless finger prick you will be able to send back a blood sample for laboratory analysis. You then receive a full breakdown for your IgG levels, and this will help to establish whether you are sensitive to foods that can provoke an IgG response. Armed with this knowledge, you will soon be on your way to feeling better.


Sian Baker

Medically reviewed by Sian Baker, Dip ION mBANT mCNHC – Written by Beth Giddings.

Updated on 1st December 2021