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Understanding Food Allergy, Intolerance and Sensitivity

Food reactivity issues seem to be on the rise: What does this mean for you and your clients, and how can you coach people to adopt appropriate nutritional solutions?

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Food Allergy and Food Intolerance

It’s almost impossible to scroll through social media without seeing ads for DIY food sensitivity tests—and with good reason. Food allergy and food intolerance are on the rise and in the public eye more than ever.

According to FARE, the largest private funder dedicated to Food and Allergy Research and Education, 85 million Americans are affected by food allergies and intolerances, and 32 million of them have a true food allergy (potentially life-threatening) (FARE 2021a). The number of children with food allergies has grown 4% every year since 2000 (FARE 2020b), and there is general agreement in the medical community that adult allergies are on the rise in the United States and other Western countries. Other nations appear to be following suit as they adopt a more westernized lifestyle (Tang & Mullins 2017).

How do you handle all the incoming information in the realm of food allergies, intolerances and sensitivities? Start by listening to your clients, who may confide in you about food issues, food sensitivity tests and restrictive diets. This article will help you meet their questions with a basic understanding of this topic, including what distinguishes food allergies from intolerances and sensitivities, how these issues can impact health and fitness, and when it’s appropriate to seek nutritional or medical guidance.

Pass or Fail Test for Food Allergy?

In addition to people who have bona fide food allergies, there are plenty of people who think they have a food intolerance or allergy but probably don’t. In one study, 19% of adults reported having a food allergy, though researchers estimated that only 10.8% of the group were correct about that (Gupta et al. 2019).

While “unconventional” food sensitivity tests (like mail-away blood and hair samples and online quizzes) may seem to be a perfect first step for uncertain consumers, they are frequently quite inaccurate and often misleading, according to Janice Vickerstaff Joneja, PhD, owner of Vickerstaff Health Services. Joneja was head of the first clinic in Canada catering to the dietary management of food allergy, which opened in 1991 at Vancouver Hospital and Health Sciences Centre. “People are paying a lot of money and being told they’ve got a whole range of intolerances that they may not have.”

Diana Munoz-Mendoza, MD, assistant professor of allergy and immunology at the University of Arkansas for Medical Sciences, says this can be harmful. “Food sensitivity testing and online quizzes about food allergies and intolerances can lead to extensive elimination diets that can cause nutritional deficiencies without treating the underlying cause of symptoms,” she says.

Laura Gibofsky, MS, RD, CDN, who works with children and adults at the Hospital for Special Surgery in New York City, says, “We are also seeing a lot of eating disorders related to dietary restriction due to perceived food intolerances and allergies.” (See “Tests That Don’t Pass the Test,” below, for a list of unproven or disproven approaches to diagnosis.)

Bottom line: Any management of a food sensitivity of any type must involve a dietary professional to ensure that if you take a food out of the diet, you put something back that is nutritionally equivalent—to avoid problems related to dietary restrictions.

Of course, it’s out of scope for fitness professionals without appropriate nutrition credentials to provide specific dietary guidance, says Gibofsky, who doesn’t hand out individualized exercise advice either. “We shouldn’t be crossing paths, the same way a painter doesn’t do plumbing,” she says. “The goal should be us working together to achieve optimal health.”

See also: Eat Well, Breathe More Easily

What’s the Difference?

Bread slice with a sad face cut into it

Symptoms of food allergies and intolerances overlap with each other.

So, what are food allergies, food intolerances and food sensitivities—and why is it important to understand the nuances? “Understanding the differences is important because appropriate testing and treatment are not the same for each,” says Munoz-Mendoza.

“Food allergy is a type of immune system reaction [usually] to a specific protein in a food. Food intolerance refers to difficulty digesting or metabolizing a particular food component.”

Food sensitivity, as a term, is still in debate, she adds. It is generally used to describe an inappropriate activation of the immune system to a food component—but one that does not produce antibodies or potentially lead to anaphylactic shock. However, notes Joneja, many practitioners use the term “food sensitivity” broadly, to cover any adverse reaction to food.

Symptoms of food allergies and intolerances overlap with each other and with signs of other medical conditions, including life-threatening issues. (See “Some Problems With Self-Diagnosis,” below.) This is why it is essential for anyone who suspects a food allergy to be evaluated by medical professionals, including an allergist (FARE 2021c).

Here’s more detail on each of these three categories of food reactivity.

Food Allergy

A food allergy develops when someone consumes a food component and the immune system creates immunoglob-ulin E (IgE) antibodies. When the body is exposed to the allergen again, the IgE antibodies recognize it and immediately mount an attack. This causes the release of histamine and other powerful chemicals called inflammatory mediators, which cause allergic reactions like hives, breathing problems and digestive distress—and, in the most severe cases, can lead to anaphylactic shock and death.

Food allergies emerge most commonly in childhood, but they can show up throughout adulthood, as well. In a JAMA Network Open report on a study of more than 40,000 people, 48% of food-allergic adults reported that their allergy had developed in adulthood, not childhood (Gupta et al. 2019).

A food allergy is more likely to develop in people with other food allergies; other allergic diseases (e.g., eczema, hay fever and asthma); and/or a family history of food allergies (NIAID 2018). Some people experience food allergies as part of the Atopic March or Allergic March, which refers to a progression in allergic conditions throughout a person’s lifetime. The Atopic/Allergic March begins with eczema and moves on to food allergy, allergic rhinitis and asthma. This does not happen in everyone with allergies (FARE 2021c).

While any type of food can trigger an allergic response, the eight food proteins that most commonly spark allergic reactions are found in cow’s milk, eggs, fish, peanuts, shellfish, soy, tree nuts and wheat (FARE 2021c), and FARE has most recently added sesame to the list, as well (FARE 2021d). In rare cases, carbohydrates can also cause allergic reactions (Collins 2021).

Reactions can range from mild to severe and can affect any organ system. A mild reaction may be a few hives or minor abdominal pain. A severe reaction can lead to anaphylaxis, which can cause a dangerous drop in blood pressure, syncope (loss of consciousness) and death if not treated immediately with an intramuscular injection of epinephrine (Collins 2021; AAAAI 2020).

An allergic reaction will occur usually within a half-hour or up to 2 hours after consuming the food component. Symptoms typically impact multiple body systems, including the immune, digestive, respiratory and cardiovascular systems. An allergic reaction will happen every time the person consumes or comes into contact with the food, though the severity may vary.

Skin-prick allergy testing, blood tests and food elimination diets may be conducted, but an oral food challenge (which involves exposure to foods in a clinical environment) is the gold standard for diagnosis of food allergy (Collins 2021).

There is currently no cure for food allergies, though researchers are working on preventive and therapeutic measures. Because food allergies are unpredictable, it is necessary to completely avoid foods to which one is allergic: A bite of a food that triggers a mild reaction one day can result in anaphylaxis on another day (or even a bit later in the same day).

See also: The Big 8 Food Allergens May Become 9

Food Intolerance

One of the most important differences between food allergies and intolerances is that food intolerances are not the result of an immune response, so they are typically not life-threatening.

With a food intolerance, the body is often unable to digest, metabolize or absorb a particular food component. This causes a biochemical or physiological reaction—such as the release of byproducts or the buildup of a chemical in the body—which leads to symptoms. For example, people with lactose intolerance lack the enzyme lactase to break down lactose—a sugar in milk products—so it ferments in the digestive tract, causing a buildup of gas that presents as bloating and other GI discomfort.

The food components most likely to cause food intolerance are lactose; histamine; fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs); and caffeine.

    Lactose is a protein found in cow’s milk and some dairy foods derived from milk.

    Histamine is found in fermented foods, legumes, shellfish, smoked meats, and certain fruits and vegetables.

    FODMAPs include fructose, lactose, mannitol, sorbitol, galacto-oligosaccharides and fructans.

    Caffeine is naturally occurring in coffee and chocolate and may be added to foods such as power bars and energy drinks (Thieme-Burdette 2020).

While symptoms can occur soon after eating, they can also occur later or build over time—particularly if a person consumes more of the problematic foods over the course of a day. Symptoms of an intolerance typically start in the digestive tract and include abdominal pain, bloating, gas, nausea and diarrhea, but some symptoms, especially of histamine intolerance, affect other organs in the body.

There’s no definitive test to diagnose food intolerances. Once an allergist has ruled out food allergy (an essential first step), a gastroenterologist may suggest a food elimination diet, which involves removing most foods from the diet and adding them back in while observing the physical response. Management of food intolerance may include limiting intake of a food and taking enzyme supplements to improve digestion (e.g., lactase to break down lactose).

Because of the range of severity and timing of symptoms and the lack of a diagnostic test, it’s difficult to estimate how many people have food intolerances; however, some are more prevalent than others. The Global Autoimmune Institute reports that lactose intolerance affects 65% of the world’s population in adulthood, and histamine intolerance about 1% (Thieme-Burdette 2020).

Food Sensitivity

The term food sensitivity is not an official medical diagnosis, but the term is increasingly used to describe adverse food reactions that can involve immune system activation without the creation of IgE antibodies. Unlike with food allergies, food sensitivities do not pose a risk of anaphylaxis, so they are not life-threatening. And unlike intolerances, food sensitivity symptoms can affect systems beyond the GI tract. This category is now being used to identify food issues that are not caused by a food allergy or food intolerance.

Symptoms of food sensitivities can be tricky to spot because they can happen right away or up to a few days later. A food elimination diet, along with a food log and family and personal health history, can help identify food sensitivities.

The most common food components that patients have reported as causing sensitivities are gluten, casein (in milk and foods derived from milk), eggs, corn, soy, yeast, citrus, nightshade family produce (tomatoes, eggplants, peppers, goji berries), legumes (including peanuts), nuts and food additives (Thieme-Burdette 2020).

How Food Allergy and Food Issues Can Affect Exercise

Woman with food allergy scratching neck

There are several ways food reactivity can affect workouts and other fitness goals.

Fitness professionals are well aware that nutrition and recovery are every bit as important as training, regardless of the client’s specific goals. When someone has food allergies, intolerances or sensitivities, addressing them can have a significant impact on how the person’s body responds to a workout, as well as numerous other factors.

In a small study of elite athletes (12 men, 10 women), medical professionals administered questionnaires and physical tests, then provided each participant with a customized food elimination diet based on the results. After following their individual diets for 3 months, the athletes showed a significant reduction in body fat (though no change in weight), improved heart rate response and increased flexibility, as well as a declining level of food intolerance (Kostic-Vucicevic et al. 2016).

Here are a few other ways food reactivity can affect workouts and other fitness goals:

Asthma. Food allergies and asthma may coexist, and exercise has the potential to trigger or worsen asthma symptoms (Ziegelbaum 2020). This is another reason to recommend that clients with food allergy and/or asthma concerns or symptoms be tested and that they bring appropriate rescue medications to every workout.

Food-dependent exercise-induced anaphylaxis (FDEIA). This type of food allergy can be unpredictable and life-threatening. In FDEIA, the person has an allergic reaction only when a particular food component is ingested a few hours before exercise (most commonly vigorous exercise). It is difficult to diagnose because symptoms may not show up for 1–4 hours after consumption of the food. If the person eats the same food at rest or exercises before eating the food, the symptoms don’t occur.

Inflammation. The gut microbiome may influence how the body reacts to certain foods. In some cases, the lining of the intestine can become permeable—a condition sometimes referred to as leaky gut. This allows movement of molecules from the intestinal tract into the bloodstream, where the immune system attacks them. The result can be chronic inflammation (Thieme-Burdette 2020).

Mental health. Managing a food allergy can impact mental health, both for those with the allergy and for caregivers. People with a restricted diet may struggle with social anxiety or depression, and it is common for parents (especially mothers) of food-allergic children to experience anxiety. In addition to referring a client to a mental health professional as needed, fitness professionals can provide support by validating their clients’ feelings and encouraging people to focus on the benefits of adhering to their treatment plan (Collins 2021).

Performance. We’ve all known people who struggle with GI symptoms surrounding competitive events. Regardless of how normal this may seem, it warrants a discussion with at least the primary care provider, as the cause may not simply be “pre-race jitters.”

Extensive elimination diets can also impact performance if they are not created by a nutrition professional. Self-restricting can lead to deficiencies in macronutrients (like muscle-building protein) and micronutrients (like bone-building calcium, vitamin D and many others). This can affect current and future performance as well as the recovery period between competitions.

Weight. Some studies have found that children with food allergies (especially multiple ones) are below average weight for their age.

Adults are generally more concerned about weight gain. Research has not shown a link between food allergies or intolerances and weight gain. However, adults with these and similar conditions may notice abdominal bloating that can mimic the appearance of excess weight (Amidor 2020).

For adults who are looking to lose weight, Joneja notes that it is vital to diagnose and treat any food allergies and intolerances, if present, and to stabilize the diet before turning the attention to weight loss.

See also: FODMAP Gut Check: Test Your Knowledge

10 Ways Fitness Pros Can Help

Trainer helping client with food allergy

Refer your client to his or her primary care provider if you suspect that the client has a food allergy.

For fitness pros, it can be challenging to understand scope of practice regarding nutrition. Find out what your state legally requires regard-ing nutrition coaching, so you are sure to stay within your arena of authority (Muth 2015). Start with the website for the Commission on Dietetic Registration (cdrnet.org), the credentialing agency for the Academy of Nutrition and Dietetics. Also check what your fitness certification says on this topic.

Here are 10 other things fitness professionals can do (FAACT 2021; Joneja 2013):

  1. Ask clients about food allergies and intolerances when doing initial assessments as well as follow-ups, just as you would with other health conditions.
  2. Get to know local registered dietitians who specialize in food allergies and intolerances. You may want to partner with one of these RDs if you’d like to focus on training people with food issues. Searching is easy on EatRight.org’s “Find a Nutrition Expert” page (EatRight 2021).
  3. If you suspect that a client may have a food allergy or intolerance or is engaging in restricted or disordered eating, refer the client to his or her primary care provider right away. The physician can assess the symptoms and refer the client out for further allergy testing or tests to rule out a possible pathology.
  4. When working with people with a medical diagnosis of food allergy, encourage them to talk with their doctor or dietitian if their eating plan is not working for them or if they want to lose or gain weight.
  5. Ask to see the list of foods a client does not have to restrict, so you can share recipes or cooking tips to make it easier to stick to the prescribed eating plan.
  6. Seek additional training and certification in nutrition. At least 10 fitness organizations offer additional training in nutrition. You can also learn more about food allergies specifically by enrolling in the free FARE Food Allergy Academy, which offers online classes, interactive trainings and educational content.
  7. Help clients learn how to read food labels. While healthcare providers and registered dietitians will alert clients to what they must avoid, you can reinforce where to find key information on food packaging.
  8. Discourage clients from sharing food or bringing unlabeled food products (e.g., homemade snacks) into your professional setting. You never know whether clients have an allergy that they haven’t disclosed or that is not diagnosed.
  9. Double-check. Make sure clients with food allergies (or other life-threatening allergies) always bring emergency medication—including antihistamines and an auto-injectable epinephrine device—to the gym or wherever you are working with them.
  10. Guide clients toward reputable resources for additional information, such as research studies that call into question the validity of unconventional food sensitivity tests.

Have Food Allergies? Consider Going the Extra Mile

If you have food allergies, you can play an additional and extremely helpful role, at the cost of just a few minutes now and then: Join the FARE Patient Registry®, which tracks more than 12,000 people’s responses to more than 200 allergens, from acai to zucchini. Initially, you’ll complete a profile and take some surveys, and later you may be asked to log food reactions at times or answer other questions—all with strict anonymity.

One recent FARE study reported that at least 50% of respondents experience at least one allergic reaction per year—with nearly 10% coming from intentional exposure to a food they know they’re allergic to (FARE 2020a).

“Every food allergy patient’s experience is unique, so the more patients who join and contribute to this Registry, the richer the data will be for medical researchers, like myself, who are seeking to understand as much as we can about life with food allergies,” says Ruchi Gupta, MD, MPH, FARE’s medical adviser for public health and education. “This data will help speed the development of life-changing treatments and improve patient care” (FARE 2020a).

Tests That Don’t Pass the Test

A 2018 study by John M. Kelso, MD, of the Scripps Clinic’s Division of Allergy, Asthma, and Immunology in San Diego, looked at the body of research on various “unconventional testing” approaches for food allergy. He concluded that all the following tests were “unproven, or in many cases disproven”:

  • the ALCAT test
  • allergen-specific IgG/IgG4 food tests
  • intradermal provocation-neutralization tests
  • hair analysis
  • electrodermal testing
  • applied kinesiology

The National Institute of Allergy and Infectious Diseases also lists the following tests as “non-
standardized, unproven, and . . . not recommended for the routine evaluation of the IgE-mediated food allergy” (FARE 2021b):

  • basophil histamine release/activation
  • lymphocyte stimulation
  • facial thermography
  • gastric juice analysis
  • endoscopic allergen provocation
  • cytotoxicity assays
  • mediator release assay (LEAP diet)

(EatRightPRO 2021)

For readers who’d like to dig deeper, the details of these tests can be quite interesting and even surprising. Case in point: The applied kinesiology test involves a person holding the suspected food allergen in an extended hand while someone else presses down on that arm. It is based on the belief that when a body part is near an allergen, it will show weakness.

Learn more from the FARE website’s “Unproven Diagnostic Tests” article (FARE 2021b). The more you learn, the better you can make a case for seeking out reputable resources, information and healthcare professionals.

Some Problems With Self-Diagnosis

Let’s start with the worst-case scenario: People who have a legitimate food allergy are taking their life in their hands if they avoid diagnosis and appropriate treatment because they think they can “handle it” on their own or because they believe they have a “sensitive” stomach. A recent study by FARE found that emergency room visits due to food-induced anaphylaxis—a life-threatening reaction to a component found in a food—have more than tripled over the past decade (FARE 2020).

“A food allergy is difficult to miss because it occurs almost immediately after the offending food is consumed and usually involves skin, in the form of hives or swelling. However, symptoms from food allergy, intolerance or sensitivity that involve mainly the gastrointestinal tract can be vague or mimic other medical conditions,” says Diana Munoz-Mendoza, MD, assistant professor of allergy and immunology at the University of Arkansas for Medical Sciences. Those conditions may include a bacterial or viral infection, an eating disorder, motion sickness, stress, ulcers, or an adverse reaction to a medication (ACAAI 2021).

“Appropriate diagnosis is important, [so that people] know which foods could potentially cause a life-threatening reaction,” says Munoz-Mendoza. Appropriately ruling out a food allergy is also important, she adds, because an incorrect assumption can lead to unnecessary diet restrictions. It can also delay the actual diagnosis.

Moreover, when people say they have a food allergy but don’t, they can indirectly harm people who do. For example, if people say they’re allergic to peanut butter (when they are really just avoiding it to lose weight), that perpetuates the misperception that food allergies aren’t all that serious. “You have the right to not have a food you don’t want,” says Laura Gibofsky, MS, RD, CDN, who works with children and adults at the Hospital for Special Surgery in New York City. “But you don’t want to take the truth of someone [with a food allergy] and make it your own when that’s not the case.”

Key Differences: Food Allergies Versus Intolerances Versus Sensitivities

This is a summary based on information from the American Academy of Allergy, Asthma & Immunology (AAAAI 2020; AAAAI 2021) and the Global Autoimmune Institute (Thieme-Burdette 2020). It can make it a bit easier to understand the basic differences between food allergies, intolerances and sensitivities.

Food allergy, intolerance and sensitivity chart

Source: Adapted from Birch & Anzman-Frasca 2011.


AAAAI (American Academy of Allergy, Asthma & Immunology). 2020. Food intolerance versus food allergy. Accessed July 30, 2021: aaaai.org/Tools-for-the-Public/Conditions-Library/Allergies/food-intolerance.

AAAAI. 2021. Food intolerance defined. Accessed Aug. 1, 2021: aaaai.org/Tools-for-the-Public/Allergy,-Asthma-Immunology-Glossary/Food-Intolerance-Defined.

ACAAI (American College of Allergy, Asthma & Immunology). 2021. Nausea and vomiting. Accessed Aug. 1, 2021: acaai.org/allergies/symptoms/nausea-and-vomiting/.

Amidor, T. 2020. Ask the expert: Can food allergies cause weight gain? Today’s Dietitian, 22 (9), 8.

Collins, S.C. 2021. Food allergies/sensitivities: Adult-onset food allergies. Today’s Dietitian, 23 (5), 14.

EatRight. 2021. Find a nutrition expert. Academy of Nutrition and Dietetics. Accessed July 30, 2021: eatright.org/find-a-nutrition-expert?rdType=url_edit&rdProj=fane_update&rdInfo=fae.

EatRightPRO. 2021. Diagnosing food allergies: Current guidelines. Academy of Nutrition and Dietetics. Accessed July 30, 2021. eatrightpro.org/news-center/nutrition-trends/diseases-and-conditions/diagnosing-food-allergies-current-guidelines.

FAACT (Food Allergy & Anaphylaxis Connection Team). 2021. Tips for the newly diagnosed. Accessed July 30, 2021. foodallergyawareness.org/food-allergy-and-anaphylaxis/.

FARE (Food Allergy & Research Education). 2020a. FARE patient registry. Accessed Aug. 1, 2021: foodallergy.org/research-innovation/elevating-research/fare-patient-registry.

FARE. 2020b. The food allergy consumer journey. Accessed July 29, 2021: foodallergy.org/food-allergy-consumer-journey.

FARE. 2021a. Food allergy awareness week. Accessed Aug. 31, 2021: foodallergy.org/our-initiatives/awareness-campaigns/food-allergy-awareness-week.

FARE. 2021b. Unproven diagnostic tests. Accessed July 30, 2021: foodallergy.org/resources/unproven-diagnostic-tests.

FARE. 2021c. What is a food allergy? Accessed July 30, 2021: foodallergy.org/resources/what-food-allergy.

FARE. 2021d. Sesame allergy. Accessed Sep. 1, 2021: foodallergy.org/living-food-allergies/food-allergy-essentials/common-allergens/sesame.

Gupta, R.S., et al. 2019. Prevalence and severity of food allergies among US adults. JAMA Network Open, 2 (1), e185630.

Joneja, J.V. 2012. The Health Professional’s Guide to Food Allergies and Intolerances. Cleveland: Academy of Nutrition and Dietetics.

Joneja, J.V. 2013. Food Allergies and Intolerances: Client Education Tools for Dietary Management. Cleveland: Academy of Nutrition and Dietetics.

Kelso, J.M. 2018. Unproven diagnostic tests for adverse reactions to foods. The Journal of Allergy and Clinical Immunology: In Practice, 6 (2), 362–65.

Kostic-Vucicevic, M., et al. 2016. O-35 Is there a connection between food intolerance and sports performance in elite athletes? British Journal of Sports Medicine, 50 (Issue Suppl. 1).

Muth, N.D. 2015. Nutrition coaching: Scope of practice. IDEA Health & Fitness Association. Accessed July 30, 2021: ideafit.com/uncategorized/nutrition-coaching-and-scope-of-practice/.

NIAID (National Institute of Allergy and Infectious Diseases). 2018. Identifying causes of food allergy & assessing strategies for prevention. Accessed July 29, 2021: niaid.nih.gov/diseases-conditions/food-allergy-causes-prevention.

Tang, M.L.K., & Mullins, R.J. 2017. Food allergy: Is prevalence increasing? Internal Medicine Journal, 47 (3), 256–61.

Thieme-Burdette, M. 2020. Environmental health: Food sensitivity, intolerance, or allergy: What’s the difference? Global Autoimmune Institute (GAI). Accessed Aug. 1, 2021: autoimmuneinstitute.org/articles/food-sensitivity-intolerance-or-allergy/.

Ziegelbaum, L. 2020. The relationship between food allergies and asthma. Today’s Dietitian, 22 (4), 44.

Laura Quaglio

Laura Quaglio has more than 25 years’ experience in health and fitness writing and editing, including several CEC/CEU courses for NASM and IDEA. Her work has appeared in IDEA’s Fitness Journal, American Fitness, Fit Pregnancy and numerous Prevention Health Specials. She has also worked on course materials for NASM, including the new CPT (7th ed.).

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