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    Food Allergies & Sensitivities: All the Science You Need to Know


    It seems like everyone is talking about what they can and can’t eat these days: supermarket aisles are lined with products claiming to be gluten-free, dairy-free, nut-free, soy-free, and everything in between. Suffice to say, food allergies, food sensitivities, and food intolerance are a hot topic in nutrition and health right now. There have been new diet trends and entire patterns of eating designed around the idea that people may be “sensitive” to certain foods, and that this sensitivity can cause negative reactions like inflammation and fatigue. From dietitians and physicians to news anchors and journalists, there are a lot of people talking about the subject; but is there solid science to back it up?

    Examining the science is what InsideTracker does best! We’ll dissect the issue in this blog and present the most current research on food allergies and sensitivities. If you do your own reading on food allergies, you’re sure to run into plenty of scientific terms – some of which may be confusing – so we’ll save you the struggle and in simple terms, break down different types of food allergies, the tests currently used, and the scientific evidence that supports them. It’s dense, but it’s worth it! At InsideTracker we follow evidence based nutrition; meaning that everything that we recommend is supported by qualified scientific research.
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    First, The Basics

    In general, an allergic reaction occurs when your body mistakes a harmless protein or molecule as a “threat” to itself. Whether this “threatening invader” is pollen, peanut proteins, or cat dander, your body will respond with an immune reaction that triggers the production of antibodies. Antibodies help your body get rid of molecules that could potentially harm it, and are very important for fighting disease and keeping us healthy. Antibodies are also what cause the symptoms (think inflammation, runny nose, sneezing, etc.) of an allergic reaction.

    Food allergies work the same way as other allergies. When you are allergic to a food, it is actually specific components of the food that make the body react. When you eat this food that your body thinks is harmful, it responds by producing antibodies to defend itself. The antibodies cause symptoms – this is an allergic reaction. We’re going to talk about antibodies a lot in this post, because they are usually measured in tests for food allergies/sensitivities. The type of antibody that is made can also be what differentiates a food allergy from a food sensitivity.


    Food Allergy (a.k.a. Type 1 Hypersensitivity)

    A food allergy is an immediate, intense allergic reaction to a food. This type of allergic reaction is also known as a type 1 hypersensitivity, and can be very serious in some people. This type of severe allergic reaction is characterized by an immediate rise in the antibody IgE.1

    So, when we talk about food allergies, we mean intense reactions that can be extremely uncomfortable, or even life threatening. Because of the intensity of the reaction, these types of allergies are fairly clear-cut when it comes to making a diagnosis. Based on your symptoms, your doctor will make a clinical diagnosis and then order allergy tests to confirm the diagnosis.

    The most common tests used to diagnose a food allergy are:

    • Skin prick test: A small amount of purified allergen is gently scraped or pricked onto the skin surface. This test is highly sensitive, but can also result in false positives. This means that even if you get an allergic response, you may not actually be allergic to the food. This test is better at confirming that you are not allergic to something.
    • Food challenge: The subject is fed food in increasing doses until an allergic reaction occurs. This is the most accurate food allergy test, but must be done with an allergist at a medical facility to avoid a serious allergic reaction.
    • Laboratory tests (In Vitro Immunoassay): Blood tests measure for antibody levels in reaction to different foods. A blood sample is taken and exposed to several different components of food (allergens) that can cause an allergy. If you react to these foods, antibodies in your blood will bind to these allergens, and this can be measured.These tests are typically done in conjunction with one of tests listed above.1

    A food allergy can be very serious, and it is important to follow your doctor’s orders for dealing with the foods you’re allergic to. Some classic examples of foods that can cause allergic reactions are peanuts/tree nuts, seafood, and soy. Managing a food allergy typically includes avoiding these foods, or carrying an EpiPen just in case you are exposed. There is no real “gray area” when dealing with food allergies. Do what your doctor tells you to do.


    Food Sensitivity/Intolerance (a.k.a. Type 2 Hypersensitivity)

    “Food sensitivity” and “food allergy” mean two very different things, but these terms are often confused. Unlike food allergies, food sensitivities are less understood, and methods for accurately testing for them are still being researched. A food sensitivity is also known as a type 2 hypersensitivity, and is thought to be a chronic, low-level allergic reaction.

    There are no established biomarkers or tests for food sensitivity, but recently, research has been examining the antibodies IgG and IgA as markers of this type of reaction. Unlike the food-allergy antibody IgE, which increases immediately after exposure to an allergen, it is thought that the antibodies IgG and IgA slowly increase in the hours after exposure to certain foods, and remain elevated for a longer period of time. This is thought to lead to low-grade, chronic, allergic reaction conditions. IgG/IgA-mediated food sensitivity has been shown to be associated with symptoms like Irritable bowel syndrome (IBS), migraines, rashes, asthma, and chronic fatigue.2

    Recently, there has been a great deal of popular interest in this new research on food sensitivity, and it has been used as the basis for trends like gluten-free and lactose-free diets. The idea behind these trends is that by eliminating foods containing “allergens” from your diet, you will improve your health by supposedly reducing these low-grade, chronic allergic reactions. The most common foods thought to cause sensitivity are wheat, dairy, and corn. The problem with this, though, is that if you are not actually sensitive to these foods, following this special diet is not helping you. In fact, you may be missing out on certain nutrients contained in the foods you are avoiding. Unfortunately, the answer to this argument is not as simple as “okay, then I will get tested to see if I have a food sensitivity.” Testing IgG and IgA is really only useful if you are having symptoms of a sensitivity.

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    To test IgG and IgA, laboratories use ELISA to quantify the antibody response to specific foods, and then interpret the results in clinical context. What this means is they take a sample of blood, and expose it to hundreds of different food solutions. If more than 3 items in any food family create a positive allergic reaction (increase levels of IgG/IgA), the person is recommended to eliminate foods from that family for 4-6 months. If eliminating these foods reduces the symptoms the person was having, then a diagnosis of food sensitivity can be made.

    Having symptoms of food sensitivity is an important factor in considering the benefits of antibody testing, because there are high levels of false positives (diagnosed as sensitive to a specific food, but in reality, not sensitive to it) when using antibody levels to test for sensitivity. A study in 2012 measured IgG antibodies against common food allergens in people with Irritable Bowel Syndrome (IBS) and in healthy people without any symptoms. They found elevated IgG in 50% of the people with IBS, but also in 15% of healthy people with no symptoms!3

    This research shows that there is a high rate of false positives when using these antibodies to diagnose food sensitivity. Based on this, food allergy tests should only be used if there are symptoms of a food sensitivity. If you don’t have any symptoms, you might still get positive results for a sensitivity, but eliminating these foods from your diet may not have positive benefits.


    Is there any use for food sensitivity testing?

    If you are having symptoms of a food sensitivity such as IBS, antibody testing has been shown to be effective in identifying foods in your diet to eliminate. A research group in 2004 had subjects with IBS either follow an elimination diet based on their IgG testing, or a random elimination diet (placebo). The group that eliminated foods based on the IgG test had 10% greater reduction in IBS symptoms than the placebo group after 12 weeks.4 Findings from a similar study in 2012 support these results. In this study, a group of subjects with IBS followed an elimination diet based on their antibody results. After 12 weeks all IBS symptoms had decreased significantly (see graphs below).3

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    Let’s recap the science...

    Food allergy and food intolerance are two very different things. A food allergy is a type 1 hypersensitivity mediated by the fast-responding antibody IgE. A food allergy will result in an immediate and intense reaction, and doctor’s instructions should be followed in managing the allergy. Food sensitivity, on the other hand, is a type 2 hypersensitivity that is possibly mediated by the slow-responding antibodies IgG and IgA. Symptoms most commonly associated with food sensitivities are IBS, migraines, asthma, and chronic fatigue. IgG and IgA are not typically used to diagnose food allergy, but their potential for mediating, and possibly diagnosing food sensitivity, is a topic of current research.

    Based on the available research, IgG/IgA testing seems to be associated with food sensitivity, but should only be used to support a diagnosis based on clinical observation or presentation of symptoms, as many of the healthy controls in studies have also shown elevated levels of IgG. If symptoms are present, this testing can be used to confirm the clinical diagnosis, and can be the basis for an elimination diet that could improve your symptoms.

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    1. [1] Mullin GE, Swift KM, Lipski L, Turnbull LK, Rampertab SD. Testing for food reactions: the good, the bad, and the ugly. Nutr Clin Pract 2010;25(2):192-8.
    2. [2] Shakoor Z, AlFaifi A, AlAmro B, AlTawil LN, AlOhaly RY. Prevalence of IgG-mediated food intolerance among patients with allergic symptoms. Ann Saudi Med. 2016;36(6):386-390.
    3. [3] Guo H, Jiang T, Wang J, Chang Y, Guo H, Zhang W. The value of eliminating foods according to food-specific immunoglobulin G antibodies in irritable bowel syndrome with diarrhoea. J Int Med Res. 2012;40(1):204-10.
    4. [4] Atkinson W, Sheldon TA, Shaath N, Whorwell PJ. Food elimination based on IgG antibodies in irritable bowel syndrome: a randomised controlled trial. Gut. 2004;53(10):1459-64.



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