There are many people and places around the world that will offer you blood tests, promising they can tell you what foods you should and should not eat.

They do this on the basis of antibodies in your body known as IgG and IgE proteins that show a certain number of antibodies that your body contains.

The blood testers claim they can tell you from the results what you should eat and what will cause you issues.

However science tells us somewhat differently. Read on (data taken from Science Today)… In short, do not waste your money on these blood tests, the data is totally unproven and indeed a waste of your hard unearned cash!

From the American Academy of Allergy, Asthma and Immunology & American College of Allergy, Asthma and Immunology: Allergy diagnostic testing: an updated practice parameter:

IgG and IgG subclass antibody tests for food allergy do not have clinical relevance, are not validated, lack sufficient quality control, and should not be performed.

And from the the American Academy of Allergy, Asthma and Immunology (AAAAI) Practice Paper, Current approach to the diagnosis and management of adverse reactions to foods[PDF]:

Some tests are considered unproven in regard to the diagnosis of specific food allergies. Those for which there is no evidence of validity include provocation-neutralization, cytotoxic tests, muscle response testing (applied kinesiology), electrodermal testing, the “reaginic” pulse test, and chemical analysis of body tissues. Measurement of specific IgG antibodies to foods is also unproven as a diagnostic tool.

From the European Academy of Allergy and Clinical Immunology [PDF]:

Testing for blood IgG4 against different foods is performed with large-scale screening for hundreds of food items by enzyme—linked immunosorbent assay-type and radioallergosorbent-type assays in young children, adolescents and adults. However, many serum samples show positive IgG4 results without corresponding clinical symptoms. These findings, combined with the lack of convincing evidence for histamine-releasing properties of IgG4 in humans, and lack of any controlled studies on the diagnostic value of IgG4 testing in food allergy, do not provide any basis for the hypothesis that food-specific IgG4 should be attributed with an effector role in food hypersensitivity.

In contrast to the disputed beliefs, IgG4 against foods indicates that the organism has been repeatedly exposed to food components, recognized as foreign proteins by the immune system. Its presence should not be considered as a factor which induces hypersensitivity, but rather as an indicator for immunological tolerance, linked to the activity of regulatory T cells. In conclusion, food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints.

From the National Institute of Allergy and Infectious Diseases Guidelines for the Diagnosis and Management of Food Allergy in the United States [PDF]:

4.2.2.9. Nonstandardized and Unproven Procedures; Guideline 12:

The (Expert Panel) recommends not using any of the following nonstandardized tests for the routine evaluation of IgE-mediated (food allergy):

  • Basophil histamine release/activation
  • Lymphocyte stimulation
  • Facial thermography
  • Gastric juice analysis
  • Endoscopic allergen provocation
  • Hair analysis
  • Applied kinesiology
  • Provocation neutralization
  • Allergen-specific IgG4
  • Cytotoxicity assays
  • Electrodermal test (Vega)
  • Mediator release assay (LEAP diet)

From the Australasian Society of Clinical Immunology and Allergy (ASCIA):

Inappropriate use of Conventional Testing: Food specific IgG, IgG4; Use: Diagnosis of food sensitivity / allergy.

Method: Antibodies to food are measured using standard laboratory techniques.

Evidence: Level II

Comment: IgG antibodies to food are commonly detectable in healthy adult patients and children, independent of the presence of absence of food-related symptoms. There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, nor that IgG antibodies cause symptoms. In fact, IgG antibodies reflect exposure to allergen but not the presence of disease. The exception is that gliadin IgG antibodies are sometimes useful in monitoring adherence to a gluten-free diet patients with histologically confirmed coeliac disease. Otherwise, inappropriate use of food allergy testing  (or misinterpretation of results) in patients with inhalant allergy, for example, may lead to inappropriate and unnecessary dietary restrictions, with particular nutritional implications in children. Despite studies showing the uselessness of this technique, it continues to be promoted in the community, even for diagnosing disorders for which no evidence of immune system involvement exists.

From the Allergy Society of South Africa, Position Statement: ALCAT and IgG Allergy & Intolerance Tests [PDF]:

We are constantly consulted by colleagues, health funders and practitioners about the reliability and appropriateness of the ALCAT and IgG food allergy tests for patients with suspected allergies and other disorders. We would like to provide the following information to the readership of the journal and to the public.
The manufacturers and suppliers of ALCAT and the IgG test claim that the tests have diagnostic value in identifying substances responsible for allergic and intolerance reactions. These tests are being marketed directly to the public and health professionals, claiming to be more effective than traditional skin prick tests or serum specific IgE tests, particularly for delayed allergic reactions.  The manufacturers of the ALCAT test argue that orthodox allergy practice does not recognize delayed allergic reactions, when in fact these reactions are universally acknowledged to play a role in up to 30% of the spectrum of allergic reactions!
To date neither ALCAT nor IgG has been shown to have any predictive value in the diagnosis of allergy or intolerances.

and

The second test marketed with insufficient documentation is the IgG test for food allergies. Specific IgE determination and its diagnostic value have been documented for over three decades in being specific for allergic disorders. Although IgG does play a role in the allergic response, there is no evidence to suggest that it has a diagnostic value in predicting food allergens or other substances that may be affecting individuals. The IgG test is also marketed as effective in predicting foods implicated in Attention Deficit Disorder and obesity. There is no published evidence for these claims.

I also found review papers from immunologists and allergy experts:

From the Department of Pediatric Pneumology and Immunology, University Children’s Hospital Charité, Berlin: Unproven diagnostic procedures in IgE-mediated allergic diseases[PDF]:

The determination of specific IgG-antibodies in serum does not correspond with oral food challenges (5). In cow’s milk intolerance proved by oral challenge, no increased IgG-antibodies could be found (6). IgG milkspecific antibody levels are similar in children with early and late-type clinical reactions (7). Furthermore, there is no evidence that IgG subclasses (8) or the IgE/IgG4 antibody ratio (9) are reliable diagnostic tools. A study of 27 children with hen’s egg allergy found that children with a positive challenge tended to have a higher IgE/IgG 4 ratio and a higher IgG1/IgG4 ratio than those with anegative challenge test, but concluded that oral provocations are still necessary to confirm diagnosis of food allergy (10). A large study in 601 newborns, infants, children and adults showed that the determination of IgA and IgM antibodies did not contribute to the diagnosis of food allergy (11). Since IgG-antibodies to common dietary antigens can be detected in health and disease (12), the determination of food-specific IgG is of no clinical relevance (13) and should not be part of the diagnostic work-up of food allergy.

From the Department of Paediatrics, National University Hospital , Singapore, Diagnostic tests for food allergy [PDF]:

INAPPROPRIATE TESTS :Food-specific IgG tests
Tests for food-specific IgG are marketed as IgG radioallergosorbent tests and vary in offering measurements of total IgG toward a food, or IgG4 with or without food immune complex assay. The measurement of such specific IgG antibodies and their subclasses, primarily IgG4, is based on the fact that the titre falls after a period of withdrawal of the specific food antigen.
Thus, some physicians opt to use such a modality to diagnose food allergies. Unfortunately, the determination of specific IgG antibodies in serum does not correspond with oral food challenges.(43) Burks et al conducted a study of antibody responses to milk proteins in patients with milk-protein intolerance proved by oral challenge, and found that no increase in IgG antibodies was noted.(44) In another study, Shek et al concluded that foodspecific IgG or IgG4 does not add any information to the diagnostic workup of food allergy.(45) Furthermore, most people develop IgG antibodies to foods that they eat, and this is a normal immune response indicating exposure but not allergic sensitisation.(20) Recent studies have shown that the IgG response may even be protective, and thus prevents or protects against the development of IgE food allergy. Hence, there is no convincing evidence to suggest that this test has any diagnostic value for allergy.

Other reviews and commentary identified included the following:

From the UK House of Lords Science and Technology—Sixth Report on Allergy:

We are concerned both that the results of allergy self testing kits available to the public are being interpreted without the advice of appropriately trained healthcare personnel, and that the IgG food antibody test is being used to diagnose food intolerance in the absence of stringent scientific evidence. We recommend further research into the relevance of IgG antibodies in food intolerance, and with the establishment of more allergy centres, the necessary controlled clinical trials should be conducted. We urge general practitioners, pharmacists and charities not to endorse the use of these products until conclusive proof of their efficacy has been established.

From the Food Allergy Initiative:

IgG Testing: This test checks your blood for the presence of food-specific immunoglobulin G (IgG) antibodies. Unlike IgE antibodies, which occur in abnormally large quantities in people with allergies, IgG antibodies are found in both allergic and non-allergic people. Experts believe that the production of IgG antibodies is a normal response to eating food and that this test is not helpful in diagnosing a food allergy.

Interestingly, IgG tests are also rejected as unproven by at least one insurer, Aetna:

IgG RAST/ELISA Testing: There is no evidence that IgG antibodies are responsible for delayed allergic symptoms or intolerance to foods.

A consumer advocacy group investigated different allergy tests, including IgG, and noted the following:

Researchers from the consumer group trialled alternative tests that claim to diagnose food intolerances through analysis of blood samples or strands of hair, changes in electric current, or resistance to pressure applied to their legs or arms. They found that:

  • The tests diagnosed 183 intolerances – although the researchers actually had just one medically confirmed allergy and one food intolerance between them
  • Identical blood and hair samples sent under different names to the same company produced different test results
  •  There was little or no overlap between test results from different companies
  • The testers felt the practitioners applied more pressure when measuring resistance for certain foods – which they were then told to avoid
  • The tests recommended excluding up to 39 foods – which could make it difficult to eat a balanced diet and lead to nutritional problems.

The tests cost between £45 and £275 each, but an expert panel of medical specialists and a dietitian that assessed the results felt that none had diagnostic value for genuine allergies or intolerances.

The UK’s Advertising Standards Authority has evaluated the marketing of the YorkTest and the claim the test is clinically validated, and noted the following:

YorkTest provided three papers to support their claims for the FoodSCAN intolerance tests and believed those showed that the presence of IgG antibodies in the blood was indicative of food intolerances. however, we were concerned that the studies were conducted on people suffering from chronic medical conditions such as IBS and migraine and considered that those findings did not support a general claim for diagnosis of food intolerance. We noted one of the studies was published in an academic peer-reviewed journal, but also noted that although the study concluded that IgG tests may have a role in the treatment of irritable bowel syndrome symptoms, it did not refer to food intolerance among the general population and also stated that futher clinical research was required. We acknowledged that the independent charity Allergy UK endorsed YorkTest’s FoodSCAN range with one of their Consumer Awards but also noted this was based on anecdotal evidence (self-reporting) that individuals felt they were benefiting from using the tests. We concluded that the evidence submitted was not sufficiently robust to prove the efficacy of the tests for diagnosing food allergy or intolerance.