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Be skeptical of any food intolerance “diagnosed” by a blood test.

Several years ago I wrote about what was then an emerging and concerning service offered by pharmacies and endorsed by naturopaths: “Food Intolerance” testing with claims that a simple blood test could identify foods that you were intolerant to. There was any to , and over time I was relieved to see most pharmacies (in Canada, at least) drop them, while one of the major purveyors seems to have closed up shop in Canada completely. Whether that was due to growing recognition that this direct-to-consumer testing was effectively useless, or some other reason, I am not sure but I was just relieved to see it disappear. Or so I thought. Like any other form of alternative medicine, there will always be the true believers – or at least those prepared to sell you a test, whether it’s validated, or not.

Recently the CBC television show Marketplace did . It’s worth watching in its entirety, but I’ll use the episode to illustrate just how IgG testing is clinically useless and arguably harmful.

Allergies and intolerances – What’s the difference?

Food allergies are reaction to food proteins. They may be categorized as immunoglobulin E (IgE)–mediated (immediate) reactions, non–IgE-mediated (delayed) hypersensitivity reactions, and mixed reactions. IgE-mediated reactions are the ones we worry about when we hear about a “food allergy”: flushing, itchy skin, wheezing, vomiting, throat swelling, and even anaphylaxis. These reactions can occur immediately following exposure, and are the consequence of the interaction of allergens with IgE. The reaction leads to the rapid release of inflammatory chemicals that trigger the reaction which is typically skin related (itching, swelling, rash) but can be severe- to life-threatening anaphylaxis.

Not all reactions follow this cascade. Non-IgE-mediated allergic reactions can cause localized (e.g., dermatitis) or generalized reactions, which are usually gastrointestinal or dermatological in nature. is a non-IgE related allergic reaction. Finally, some allergic disorders are both IgE and non-IgE mediated, such as atopic dermatitis (eczema).

Beyond the IgE mediated reactions, there are a number of possible reactions to food, some of which may be called a “food intolerance”. They include conditions like lactose intolerance, gastroesophageal reflux (GERD), and anything else attributed to food. “Intolerance” is a catch-all term.

When you see advertising promoting “Food Intolerance” testing, it’s a test for immunoglobulin G (IgG). IgG antibodies signify exposure to products—not allergy. IgG antibody testing will identify what you ate recently – there is no correlation between an IgG test result and your ability to eat that food without distress. In fact, suggests IgG may actually be a marker for food tolerance, not intolerance. Given the lack of correlation between the presence of IgG and physical manifestations of illness, IgG testing is considered as the as a tool for dietary modification or food elimination. As the Australasian Society of Clinical Immunology and Allergy notes, – in other words, it’s not useful at all:

Vega testing, kinesiology, allergy elimination techniques, iridology, pulse testing, Alcat testing, Rinkel’s intradermal skin testing, reflexology, hair analysis and IgG food antibody testing have all been proposed as being useful for diagnosing allergic conditions or food intolerances. Not only do these tests lack any scientific rationale, but have been shown to be inaccurate and poorly reproducible when subjected to careful study. Treatment based on inaccurate results is not only misleading, but can result in ineffective and sometimes harmful treatments, and delay more effective therapy.

The Marketplace sting

CBC Marketplace took a – they compared them to reality:

To test the accuracy of these food sensitivity tests, Marketplace ran several different kinds on host Charlsie Agro, including drawing blood for the IgG tests offered by Dynacare and Rocky Mountain Analytical, which is owned by LifeLabs. Both tests require a requisition from a naturopathic doctor or licensed physician. LifeLabs’ test is typically offered through naturopaths or other health outlets, however, while Dynacare’s food intolerance test is advertised and promoted directly to the consumer in its clinics. The results from the Rocky Mountain Analytical test reported intolerances to 52 foods, while Dynacare reported 30 intolerances.

Before taking the tests, Agro had tracked what she was eating. Yet both tests reported intolerances to foods she regularly consumed, with absolutely no adverse reactions. For example, Agro had a smoothie, which included flax seeds, for breakfast daily. Yet both tests suggested Agro is intolerant to flax. She also ate vegetable soup — containing barley, kidney beans and corn — without problem. Both IgG tests again claimed Agro is intolerant to these foods. Both sets of lab results also showed Agro is “intolerant” of egg whites, all milks, wheat and gluten — all foods she eats regularly without issue.

The IgG test, as expected, identified food that Agro had consumed recently – not foods that she had any difficulty tolerating. It’s easy to see how this type of testing could lead to disordered eating, potentially causing someone to totally transform their diet in the belief that they are “intolerant” to their regular diet. These tests are not harmless, as allergists noted:

Dr. Douglas Mack, a pediatric allergy, asthma and immunology specialist, argues the results of an IgG test are an indication that you had exposure to the foods — not an intolerance of them. IgG tests measure levels of an antibody known as Immunoglobulin G — or IgG, for short. “It should be used to track whether a patient actually is developing tolerance, not intolerance,” he said.

Interpreting the test otherwise is not only incorrect, but potentially hazardous to your health, Mack argues. By unnecessarily eliminating foods, he says he sees “kids that are coming in with nutritional deficiencies, with failure to grow very well.” Removing foods from your diet could also lead to development of a food allergy, especially in children, says Mack. One young patient of his developed a milk allergy after eliminating it from his diet when a food sensitivity test suggested he had a milk intolerance. “If these tests result in the harm of a child, we really gotta think twice about whether or not these labs should be offering these,” he said.

In response, both LifeLabs and Dynacare provided citations in support of their claims about IgG testing. I’d review them for you, but .

Social media hype

Instagram seems to be THE place to promote your product these days, and food intolerance advertising masquerading as unbiased testimonials are widespread. It’s reported that to promote its $490 IgG blood testing:

“If this test has any value, we will see literature that would be published to prove this test really could be useful,” Alessio Fasano, a pediatric gastroenterologist at Harvard Medical School, told BuzzFeed News. “But honestly, I haven’t seen anything like this so far. In the literature, in practice, I don’t see it.”

STATnews called the “medically dubious” quoting multiple experts who are critical of the testing:

Patients who ask Dr. Robert Wood, an allergist at Johns Hopkins Children’s Center, whether they have a food sensitivity would never undergo an immunoglobulin G test. Immunoglobulin G tests “are completely useless and do dramatic harm” because they may compel patients to unnecessarily avoid broad swaths of a healthy diet, Wood said. “In all my years of practice, I have never sent an immunoglobulin G test because they have no ability to predict food sensitivity,” he said.

And:

Dr. Martha Hartz, an allergist at Mayo Clinic in Rochester, Minn., says she frequently evaluates patients who’ve already forked over the cash for the testing. “Anytime I see a patient who’s had these kinds of tests, we get them to toss it aside,” Hartz said. “It has no relevance to anything. It is just not a test that should done.”

Believe the evidence, not the vendors

While food intolerances are non-immune by definition, IgG testing continues to be widely promoted as a diagnostic tool, and to guide dietary choices. There is no credible evidence to support IgG testing by consumer laboratories to identify food intolerances. The CBC Marketplace episode highlighted how IgG testing has the potential to harm, not help consumers. It’s not surprising, then, that major allergy and immunology organizations worldwide advise against IgG testing.

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Posted by Scott Gavura