An intolerance test is one of the fastest-growing segments in the dietary testing market. But are they accurate? And are they worth the money?

Food allergies and intolerances are on the rise, leading to a boom in at-home testing kits. But it's important to remember that these tests aren’t testing for allergies to foods – they're testing for foods which might cause symptoms like stomach aches, headaches or bloating, but not more severe reactions such as tongue and throat swelling or difficulty breathing (also called anaphylaxis).

The at-home kits involve pricking your finger, depositing drops of blood onto a special card and sending the sample off for analysis. The results are usually delivered via email within a couple of weeks. But the vast majority of these kits are not scientifically based and many contain false positives.

Most of these 'tests' are looking at IgG antibodies to specific foods present in your blood and claim that an increase suggests you are sensitive to the food. The truth is that IgG antibodies are found in all healthy adults and children without any symptoms, so this type of test is not clinically useful.

Other 'tests' include injecting you with food extracts under the skin in an attempt to reproduce the food related symptoms you have reported. These types of tests are not scientifically based and should be avoided as they may suggest long lists of foods which should be excluded from the diet unnecessarily, resulting in nutritional deficiencies and a reduced quality of life.

There are also a number of breath and urine tests which are purported to indicate intolerances by measuring your ability to break down lactose, a sugar found in milk products. The best of these is the hydrogen breath test, where you drink a liquid containing lactose and breathe into a device which measures the levels of hydrogen in your breath. This is a good way to identify whether you are unable to break down lactose and should result in a reduction of symptoms such as gas and abdominal pain.

Other tests measure your body's electromagnetic conductivity before and after a suspect food is eaten, and are claimed to show changes in the size of your white blood cells when you're allergic to a particular food. These tests should also be avoided as they have no rational scientific basis and can be harmful if they suggest multiple foods are unnecessarily excluded from the diet and are not reintroduced under the guidance of a dietitian.