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Not Worth Your Money: IgG Testing for Food Sensitivities

Bloating is uncomfortable, farting is unpleasant, and not knowing what’s causing your gastrointestinal tract to react can be debilitating.

But what if you could submit a one-time test that compared your blood against upwards of 900 common foods? Once the triggering foods are known, avoiding them makes your gut issues disappear.

Unfortunately, it's not that simple.

Here’s what this article is going to review:

  • The difference between a food allergy and a food intolerance/sensitivity.

  • How food allergies are diagnosed, which is crucial for understanding food sensitivities.

  • What the IgG test for food intolerances evaluates.

Plot ruiner: An example of expensive IgG tests that are not recommended by medical groups (US, Canada, and Europe) for diagnosing food intolerances.

The Differences Between Food Allergies and Intolerances/Sensitivities

Food Allergy

A food allergy is an adverse, inappropriate reaction launching the immune system into attack mode against a food, especially one that most peoples’ immune systems would consider non-threatening. A food allergy will have a reproducible effect every time it’s consumed (typically within two hours after consumption), although the severity of the reaction may differ.

When an “invading” food is consumed, the immune system overacts to produce food-specific antibodies called immunoglobulin E (IgE) that travel to mast cells. Mast cells release chemicals, like histamine, that produce an allergic reaction. Reactions can result in hives on the skin to trouble breathing.

Nearly any protein can cause a reaction, but there are eight common culprits leading to 90% of all allergies:

  • Milk, soy, wheat, and egg: These tend to be resolved during childhood, but can remain for life.

  • Peanuts, tree nuts, fish, and crustacean shellfish (e.g., lobster, shrimp, crab): These allergies tend to remain throughout a person’s entire life.

Food allergies aren’t common, present in only 6-9% of children and 2-3% of adults, yet food intolerances tend to be more common.

Food Intolerance/Sensitivity

A food intolerance is a non-immune adverse reaction. Rather, an intolerance is related to the body’s inability to properly digest a food (possibly due to an enzyme deficiency), sensitivity to food additives, or sensitivity to naturally-occurring substances within a food. Often, consuming a small amount of the culprit won’t result in a reaction, but this is very specific to the individual.

Symptoms of an intolerance, for instance, include headache, upset stomach, bloating, and diarrhea. Although a nuisance, an intolerance doesn't result in damage to the body.

How Food Allergies are Diagnosed

Properly diagnosing a food allergy takes time. If someone tells you one 60-minute consultation will result in a definitive answer, be weary.

Step 1: Conduct a Medical History

When a health care professional (HCP) evaluates someone for a food allergy, they're beginning to form a hypothesis, linking together the pieces of a patient's story like a puzzle. Beginning with a comprehensive set of questions within a complete medical history, questioning is a low-cost, minimally-invasive method for fine-tuning the direction of a patient's care plan.

Useful components of the medical history related to food allergies and intolerances include reviewing the following (although this is a very short list of what would be asked):

  • Was one of the most common allergenic foods ingested within 2 hours before the onset of the reaction? Within the definition of a food allergy, symptom onset should occur within this timeline.

  • Had the suspect food been ingested previously? A food allergy’s effects upon consumption needs to be reproducible over time.

  • What symptoms were experienced by the patient? This can help differentiate between a food allergy (respiratory symptoms) or a food intolerance (gastrointestinal symptoms).

Further testing may be required, which should be the decision of the HCP, especially a medical doctor who specializes in allergies.

Step 2: If Deemed Necessary, Conduct Further Testing

Multiple medical groups recommend a blood test and/or a skin prick test only after a complete medical history has been completed. Otherwise, jumping straight to testing has been deemed inappropriate and can result in mismanagement. That said, there are two tests that may help pinpoint a food allergy:

  • Blood work: If the immune system identifies a certain food as a threat, a food-specific IgE is released. Blood work is evaluating for these specific increases in IgE. For instance, if someone is allergic to cow’s milk, blood work could show an increase in circulating cow’s milk-specific IgE.

  • Skin prick test: An allergen is introduced into the top layers of the skin. If an allergy is present, it may result in "a raised, red, itchy bump and surrounding ‘flare’—[indicating] the presence of the allergy antibody. The larger the wheal and flare, the greater the sensitivity.”

Note that the IgG blood test is not recommended for evaluating food allergies (allergies test for IgE).

There are many reasons why a complete medical history is necessary when diagnosing a food allergy—one of them related to how blood work and skin prick tests are not definitive. A skin prick test could state a person is allergic to soy when they aren’t, leading to an unnecessary food restriction. The results of blood work and a skin prick test could be at odds.

Why does this happen?

  • Blood work produces results that are 70-90% sensitive and 50% specific.*

  • Skin prick test produces results that are 90% sensitive and 50% specific.

With blood work, “the presence of antibody does not indicate disease” and a food should ultimately be removed from the diet only when a person reports symptoms—not simply because blood work states that they may be allergic. Alternatively, simply because antibodies aren’t detected does not mean a person isn’t allergic (i.e., restriction may still be recommended).

For a positive skin prick test, the medical provider learns that the person’s immune system has been sensitized to the allergen, yet without any symptoms, the person is deemed not allergic.

Finally, if the medical history and previous tests point to a specific food allergy, a medically-supervised oral food challenge is the final step in a diagnosis. This test is considered the gold standard. Although a slow process, it's time well spent. A medical professional specifically trained in allergies will be present as the patient consumes increasingly larger amounts of the potential allergen. The HCP's presence is necessary, since if and when a life-threatening symptom is triggered, medical intervention is present.

Given the varying results, a trained HCP is needed to cut through the mud and provide a final answer and plan for the patient. Ultimately, avoidance of any food should occur only when symptoms develop after consumption.

*Sensitivity = the ability of a test to correctly classify a person as diseased. Specificity = the ability of a test to correctly classify a person as disease-free. The closer BOTH sensitivity and specificity are to 100%, the better the testing is at correctly diagnosing what it's intended to test for.

What About the IgG Test for Evaluating Food Intolerances?

The IgG food sensitivity test is a flawed understanding of why IgG increases in the blood. The test has neither been validated nor supported by the research, with multiple medical groups recommending NOT to pursue these tests—ever. You can read multiple position statements from the Canadian Society of Allergy and Clinical Immunology, the American Academy of Allergy, Asthma and Immunology, and the European Academy of Allergy and Clinical Immunology.

As mentioned, some food allergies present in childhood will disappear with age. For instance, research studies have shown that during childhood, someone with a cow’s milk allergy has blood work showing high levels of cow’s milk-specific IgE and low levels of IgG. As tolerance of cow’s milk improves (i.e., the allergy begins to disappear and cow’s milk is reintroduced into the diet), IgE decreases and IgG increases.

High IgG blood levels are “a marker of tolerance and prior exposure as opposed to intolerance.” Our immune system reacting is a good thing—we want our immune system to recognize and react, whether that’s recognizing a familiar friend or an invading threat. In both cases, specific antibodies will increase. The trick is correctly interpreting those antibodies.

Unfortunately, the rhetoric of companies and practitioners offering IgG tests use high IgG levels as their proof: Upon result retrieval, if the wheat-specific IgG value is increased then the assumption is, “See? Wheat produces high levels of IgG. This means you have a wheat intolerance.” That interpretation is incorrect.

Straight up, there is no easy test to evaluate for food sensitivities: They’re uncovered by a process of questioning, elimination, and challenge by reintroduction.

Take-home Message

In review:

  • High IgE could mean a food allergy is present (high = concern).

  • High IgG could mean immune tolerance and recognition (high = normal).

  • Whether it's a suspected allergy or intolerance, a complete medical history is the first step to evaluate if blood work and/or skin-prick testing are appropriate. For food allergies, ensure you’re working with a medical doctor who specializes in allergies. For food intolerances, ensure you're working with a registered dietitian.

  • Avoid spending the hundreds of dollars on an IgG food sensitivity test, especially since the test’s results are not useful. Unnecessary food restrictions can trigger an athlete's past of disordered eating, a clinically-diagnosed eating disorder, body image concerns, anxiety... all questions that should be first reviewed during that initial medical history.

The outcome of an IgG test typically results in an inappropriate restriction of foods. With a list of foods to avoid, people become hyper-aware of what they're eating, they read the ingredient's list for those foods, become much more aware of what they're eating, and are less likely to eat processed or packaged foods. Essentially, they tend to eat more whole foods and their symptoms weaken or disappear. It's not the IgG test being effective, but a healthful diet that is the trick.

Food-related symptoms can be debilitating. It’s understandable that people can be frustrated and want a quick fix or a test to tell them precisely what is causing their symptoms. But this testing doesn’t currently exist. Rather, commit to working with a medical doctor and registered dietitian to fine-tune an individualized diet that alleviates your symptoms.

Further Reading

Savilahti, E.M., Rantanen, V., Lin, J.S., Karinen, S., Saarinen, K.M., ... & Sampson, H. (2010). J Allergy Clin Immunol,125(6):1315-1321.

Abrams, E.M., & Sicherer, S.H. (2016). CMAJ,188(15):1087-1093.

Carr, S., Chan, E., Lavine, E., & Moote, W. (2012). Allergy Asthma Clin Immunol,8(12):1-2.

American Academy of Allergy, Asthma & Immunology (2020)

Stapel, S.O., Asero, R., Ballmer-Weber, B.K., Knol, E.F., Strobel, S., ... & EAACI Task Force. (2008). Allergy,63(7):793-796.

This post covers what FODMAPs are, why they can be a problem for some athletes, and why one would follow a low FODMAP diet.

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