Food Allergies vs Intolerances

Food allergy
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Recent estimates suggest that 3.6% of Americans, or approximately 1 in 25 adults, live with a food allergy or intolerance (1). However, intolerance and allergy are not interchangeable terms for the same condition; rather, they represent two distinct conditions that involve separate systems of the body. Read on to find out more about what distinguishes a food allergy from an intolerance and the ways in which they are diagnosed.


What is a food allergy?

Simply put, a food allergy is an abnormal immune response to a food carried out by the anti-body (or immunoglobin), IgE. This antibody is produced following a person’s initial exposure to a food deemed to be “threatening”. Upon repeated exposures to a food, IgE triggers the body to release massive amounts of histamine, which exaggerates the immune response and results in one or more of the following symptoms:

  • Itching in the mouth
  • Swelling of the lips and tongue
  • Vomiting, diarrhea, abdominal cramping
  • Hives
  • Worsening eczema
  • Difficulty breathing
  • Drop in blood pressure

If the allergic reaction is severe, it can lead to anaphylaxis; a life-threatening condition that can be deadly if not treated immediately with epinephrine (epi-pen).

IgE-mediated allergic reactions are the easiest to recognize given the specific symptoms that result from exposure to a threatening food. However, under the umbrella term of “food allergy” are several other allergic conditions that are somewhat more difficult to diagnose, but equally serious.

Eosinophilic Esophagitis – inflammation of the esophagus that is often caused by an allergic reaction to foods such as dairy, eggs, wheat, or soy.

Oral Allergy Syndrome – experienced by individuals with an allergy to pollen, oral allergy syndrome results in an itchy mouth, swollen lips, and a scratchy throat when raw fruits, vegetables, and tree nuts cross react with pollen.

Food Protein-Induced Enterocolitis Syndrome (FPIES) –a non-IgE mediated immune reaction to certain foods (most often cow’s milk or soy protein) that results in severe diarrhea and vomiting several hours after eating. While FPIES can occur in adults, it is most common in infants and young children (who often outgrow the condition with time).

Exercise-Induced Anaphylaxis – a rare condition where anaphylaxis is triggered by physical activity (most often running). In food-dependent exercise-induced anaphylaxis, a food, such as corn, peanuts, tomatoes, shellfish, and wheat, consumed within a few hours of exercise, triggers the reaction.


What is a food intolerance?

A food intolerance occurs when an individual improperly digests a food and experiences symptoms of gas, bloating, abdominal pain, or diarrhea. The most important distinguishing characteristic between a food allergy and intolerance is that a food allergy involves the immune system whereas an intolerance involves the digestive system. An example of a food intolerance is lactose-intolerance where the digestive enzyme, lactase, is not produced, resulting in significant digestive discomfort.


How are food allergies and intolerances diagnosed?

If you suspect that you or a family member has a food allergy, it’s important to meet with an allergist to receive a proper diagnosis. In addition to a detailed history, an allergist may perform one or more of the following tests:


Skin Prick Test

During a skin prick test, a solution containing the suspected food allergen is placed just below the skin. A raised white bump surrounded by a circle of itchy, red skin (a “wheal”) is indicative of a possible food allergy. While the skin prick test is unlikely to suggest that someone does not have an allergy to a food, when in fact he or she does (i.e. a false negative), the risk of false positives (or the test showing an allergy that does not exist) is relatively high at 50-60% (2). Attaining 100% accuracy is difficult since testing is being done through the skin, rather than the digestive tract. In addition, cross reactivity between similar foods (i.e. peanuts and green beans) can lead to a false positive result.


Blood Test

An allergist may also order a blood-test that looks for the presence of IgE antibodies. The accuracy of the blood test is comparable to skin prick tests, as similar issues, including digestion and cross-reactivity, can create false positives.


Oral Food Challenge

If the allergist is unable to provide a diagnosis based on a medical history and the results of the above two tests, he or she may perform an oral food challenge test, which is considered highly accurate. During this medically supervised test, the suspected food allergen is given in increasing doses over a period of time until symptoms are observed (at which time, medications are administered). Importantly, this test should not be performed without medical supervision due to the risk of anaphylaxis.

Tests That DO NOT Work

When it comes to food intolerances, making an accurate diagnosis is even more challenging. Many of the tests that are touted as diagnostic are based on pseudoscience at best, and at worst, falsified information. One of the more popular tests is the IgG blood test where levels of the antibody, IgG, are measured. However, IgG antibodies are a normal product of the body’s immune system and are found in people both with and without allergies. In fact, research shows that IgG antibodies actually increase in studies where people’s sensitivity to foods is lowered (3).

Other tests that have been disproven (and are summarized here) include: applied kinesiology, cytotoxicity, electrodermal testing, and hair analysis.

Now, this isn’t to say that food intolerances don’t exist. Rather, it suggests that many of the tests out there are not equipped for the complicated task of identifying food intolerances. The only gold-standard method for diagnosing food intolerances (outside of lactose intolerance) is an elimination diet. During such diets, suspect foods are removed from an individual’s diet for a period of 2-8 weeks. The resolution of symptoms, combined with the return of symptoms during a re-challenge phase, are confirmation that the suspect food is responsible for the digestive symptoms.


Can food allergies or intolerances be cured?

Maybe, but it’s a little more complicated than that.

Some food allergies, specifically milk, egg, or soy, are likely to be outgrown in childhood while others, including shellfish, tree nut, and peanut allergies, tend to be lifelong. Factors that increase the likelihood that a child will outgrow his or her food allergy are having a mild reaction, being allergic to only one food, and having eczema as the only symptom (4).

Oral immunotherapy, which involves gradually administering increasing doses of a food allergen under medical supervision, is emerging as a potential allergy treatment. However, oral immunotherapy has not been approved as a treatment option by the FDA and should only be used in clinical trials.

Food intolerances are another story. Often, the reason a food is not being digested well is because there is inflammation in the digestive tract. If you suspect a food intolerance, it’s important to rule out any medical cause, such as celiac disease, irritable bowel disease, or diverticular disease. Adding probiotics and increasing your intake of prebiotics and fermented foods can also help to create a more favourable gut environment, allowing you to better digest problematic foods.

Susan Macfarlane is a Registered Dietitian Nutritionist utilizing to help run a busy private practice in Ontario, Canada and blogs regularly for



  1. Acker WW, Plasek JM, Blumenthal KG, Lai KH, Topaz M, et al. Prevalence of food allergies and intolerances documented in electronic health records. J Allergy Clin Immunol. 2017 Dec;140(6):1587-1591. Available from:
  2. Food Allergy Research and Education (FARE). Skin Prick Tests. n.d. Available from:
  3. Philippe Bégin, Food Allergy Research and Education (FARE). Unproven and Non-Standardized Tests for Food Allergy. n.d. 
  4. Food Allergy Research and Education (FARE). WHO IS LIKELY TO OUTGROW A FOOD ALLERGY? 13 Sept 2013. Available from:

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