Food Intolerance Test (IgG): Checking for Hidden Food Reactions

Every person is unique; even identical twins can differ. The same is true of how our bodies react to food: reactions may be similar from person to person, or completely different.

Working out which foods suit you usually involves trial and error, which takes a long time and may not give a clear answer. Laboratory tests have therefore been developed to provide information that supports choosing suitable foods for each individual. One of these is the Food Intolerance Test.

The Food Intolerance Test (IgG) is a blood test that looks at which foods your body produces IgG antibodies against. This information may help you and your physician plan dietary changes together. For some people, temporarily reducing or avoiding certain foods may help improve some chronic symptoms.

Two types of immune reaction to food

The body's immune reactions to food fall into 2 main types: acute food allergy, which involves IgE, and gradual reactions, which involve IgG.

Type 1: Acute food allergy (IgE)

This type is commonly known as "allergy". It occurs when the body produces immunoglobulin E (IgE) antibodies, which trigger the release of histamine and cause sudden symptoms such as hives (urticaria), asthma (bronchial asthma) or severe allergic shock (anaphylactic shock).

It can be diagnosed by observing symptoms, by skin testing, or by measuring which substances IgE in the blood reacts to.

Management involves avoiding the trigger and using antihistamines when symptoms occur. In some cases a physician may consider treatment in which small amounts of the allergen are given regularly over a period of time, so that the body gradually adapts and reacts less to it.

Type 2: Gradual reactions (IgG)

This type is reported to be more common than the first. It occurs when the body produces immunoglobulin G (IgG) antibodies against foods or other foreign substances. Symptoms tend to develop gradually and come and go over a long period, which makes a clear diagnosis fairly difficult.

Symptoms some people notice include skin rashes, bloating, joint pain, chronic fatigue, bowel problems or migraine headaches.

IgG and chronic symptoms

IgG antibodies can bind to foreign substances to form what are called immune complexes. These circulate in the bloodstream and may deposit in tissues such as the skin, the bowel wall, the kidneys or blood vessel walls, prompting the body to produce substances associated with inflammation.

Because the foods we eat vary widely in type and amount, the reaction is usually not obvious at any one time. Instead, it may show up as mild chronic symptoms that come and go.

Research in this area is ongoing, and it has been hypothesised that IgG reactions to food may be a contributing factor in a number of symptoms and conditions. However, the scientific evidence is not yet clear, and these symptoms can have other causes too. Examples of conditions that have been hypothesised include:

• Muscle aches and joint inflammation
• Chronic fatigue, low mood and attention problems
• Digestive disorders, chronic diarrhoea and acid reflux
• Itchy rashes and acne
• Headaches and migraine
• Ear inflammation and fungal infections

Symptoms that may be linked to food intolerance

The following are examples of symptoms some people find may be linked to intolerance of certain foods. Each of these symptoms can have many causes, so a physician should assess you before concluding that food is involved.

• Respiratory: coughing, sneezing, breathing difficulty, allergies, ear infections, snoring, bronchitis
• Immune: frequent fevers or infections, mouth ulcers, fungal infections
• Nervous system: feeling sluggish, clumsiness, headaches, migraine, stress, memory problems
• Skin, hair and nails: dermatitis, hives, red rashes, hair loss, brittle nails, dandruff
• Metabolism: irritability, unexplained weight gain or loss, feeling cold
• Muscles and joints: stiff muscles or joints, tendon or joint inflammation
• Nutritional deficiencies: fatigue, poor concentration, vitamin deficiency, iron deficiency, anaemia, calcium deficiency
• Digestive: irritable bowel syndrome (IBS), diarrhoea, constipation, indigestion
• Urinary and reproductive: urinary tract infections

How the Food Intolerance Test is done

Finding out which foods trigger IgG production requires a specialised test called the Food Intolerance Test, or IgG food antibody test.

Microarray technology now allows reactions to as many as 221 foods to be tested using only about 10 microlitres (0.01 ml) of blood. The sample can be taken from a fingertip instead of a vein, which suits people who are difficult to draw blood from, such as children or older adults with fragile veins.

Reading the results

The report shows which foods your body produces IgG against, and to what degree. Where levels are high, that food may be one factor linked to chronic symptoms. Your physician may suggest reducing or avoiding it temporarily and choosing other foods that do not cause a reaction. The report also lists foods in the same group that can be eaten instead, making it easier to adjust your menu.

Results are grouped into 3 levels of reaction: red, yellow and green. Your physician will explain what each group means and what to do.

An IgG result is not a diagnosis of food allergy and should not replace testing for acute (IgE) allergy. Results should be interpreted by a physician together with your symptoms and history.

You don't need to give up a food for life

Finding antibodies to a food does not mean you can never eat it again. It shows that, at that point in time, your body is reacting strongly to that food.

Typically the food may be avoided for a period of at least about 3 months (possibly longer for children or people who also have allergies). Once symptoms have improved, it can be gradually and carefully reintroduced on your physician's advice.

In addition, not eating the same foods repeatedly and rotating your menu each week, choosing from food groups that do not cause a reaction, may help reduce the chance of developing food reactions. If you would like to follow up, you can discuss retesting with your physician.

Watch for hidden ingredients

Some foods, such as milk and eggs, are ingredients in many other dishes. If you need to avoid milk or eggs, take care with foods such as:

• Butter and cheese
• Cakes and desserts
• Fried rice and stir-fried noodles
• Spaghetti sauces

Keep your nutrition balanced

When people learn they react to certain foods, many become anxious and try to cut out several foods at once. Whatever your results, it is important to keep your diet balanced and to pay more attention to the foods you choose.

To make sure you get all the nutrients you need each day, adjust your diet following a guide under the care of a specialist physician, rather than eliminating foods on your own.