Introduction
When people come to me because they think they may be allergic to certain foods, the first thing I ask is if they have an allergy to any trees or grasses. This may seem like a strange question, but some people who are allergic to tree or grass pollen may have symptoms when eating certain foods because the pollen of the tree or grass is similar to the pollen that forms the fruit or vegetable, and the body recognizes the similarity. This is known as cross-reactivity.
A person who is allergic to a tree or grass pollen reacts to the food — not because they are allergic to the food itself, but because they are allergic to a pollen from a tree or grass that has similar protein sequences. If a person has never been tested for environmental allergies (pollens, for example) or for food allergies, the first place I get started is to recommend that their doctor have them tested by an allergist.
What is a Food Allergy?
An allergy is an immune-system mediated reaction that results in the body producing specific allergen IgE antibodies to the substance to which they are allergic (the allergen). When people are exposed to the allergen, the specific IgE antibody binds with their mast cells, which results in the release of histamine, causing the symptoms of an allergic reaction. A true allergy always involves IgE antibodies; therefore, food sensitivity tests based on IgG antibodies do not diagnose food allergy.
Each IgE antibody is specific to one type of allergen. For example, a person with a “milk allergy” may produce IgE antibodies to β-Lactoglobulin or α-Lactalbumin—two different proteins found in the whey fraction of milk—or they may be allergic to casein. Similarly, a person allergic to a tree pollen may produce IgE antibodies to only one protein in that pollen, or to several.
Oral Allergy Syndrome (OAS) – Pollen Allergy
Most food allergies in adults who never had food allergies as children are the result of cross-reactions between food and inhaled allergens such as pollen [1]. This is known as Oral Allergy Syndrome (OAS).
If a person has seasonal allergies in the early spring, it is most likely caused by allergies to tree pollen [2], and as many as 50%—70% of people who are allergic to birch pollen will have Oral Allergy Syndrome [3,4]. Alder is another common pollen allergen that results in OAS, as is latex found in rubber trees.
OAS reactions are most often thought of involving the lips, tongue, or roof of the mouth, but some people can also experience gastrointestinal symptoms—particularly related to birch pollen allergy [5]. It can get complicated: an allergy to either birch or alder pollen results in OAS to apples, but so can an allergy to apples themselves. Only an allergist can determine the specific underlying allergen.
Testing and Diagnosis
Since an allergist is a specialized Physician (an MD), costs are covered under provincial health plans. Once a person has been diagnosed with IgE-mediated allergies, I teach them how to avoid foods to which they are allergic and to be aware of which foods may result in cross-reactivity.
When people test negative for food or pollen allergies but have GI symptoms, if this hasn’t previously been done, I will recommend that they have a blood test to rule out celiac disease (gluten intolerance).
If the person does not test positive for either IgE-mediated allergies or celiac disease, and their doctor has already ruled out other conditions such as inflammatory bowel conditions (Crohn’s or colitis), they are frequently diagnosed with Irritable Bowel Syndrome (IBS), which can be addressed with dietary support.
Final Thoughts…
I used to offer a Food Allergy/Food Sensitivity Package; however, most people would be seeking services based on IgG Food Sensitivity tests purchased through a naturpath. rather than IgE-mediated test results obtained through an allergist. I continue to support those diagnosed with IgE-mediated food allergies and, depending on the severity, will usually do so within the context of add-on services to the Comprehensive Dietary Package. You can learn about me here.
To your good health!
Joy
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References
- Pong AH. Oral allergy syndrome. Vaughan (ON): Allergy/Asthma Information Association (AAIA); 2000. [https://www.calgaryallergy.ca/articles/english/oral_food_allergy.htm]
- Sussman G, Sussman A, Sussman D. Oral allergy syndrome. CMAJ. 2010 Aug 10;182(11):1210-1. [https://www.cmaj.ca/content/182/11/1210]
- Mogensen JE, Wimmer R, Larsen JN, et al. The major birch allergen, Bet v 1 shows affinity for a broad spectrum of physiological ligands. J Biol Chem. 2002 Jun 28;277(26):23684-92. [https://pubmed.ncbi.nlm.nih.gov/11953433/]
- Hoffmann-Sommergruber K, O’Riordain G, Ahorn H, et al. Molecular characterization of Dau c 1, the Bet v 1 homologous protein from carrot and its cross-reactivity with Bet v 1 and Api g 1. Clin Exp Allergy. 1999 Jun;29(6):840-7. [https://pubmed.ncbi.nlm.nih.gov/10336602/]
- Rentzos G, Lundberg V, Stotzer PO, et al. Intestinal allergic inflammation in birch pollen allergic patients in relation to pollen season, IgE sensitization profile and gastrointestinal symptoms. Clin Transl Allergy. 2014 May 30;4:19. [https://pmc.ncbi.nlm.nih.gov/articles/PMC4048541/]
© 2025 BetterByDesign Nutrition Ltd.
Joy is a Registered Dietitian Nutritionist and owner of BetterByDesign Nutrition Ltd. She has a postgraduate degree in Human Nutrition, is a published mental health nutrition researcher, and has been supporting clients’ needs since 2008. Joy is licensed in BC, Alberta, and Ontario, and her areas of expertise range from routine health, chronic disease management, and digestive health to therapeutic diets. Joy is passionate about helping people feel better and believes that Nutrition is BetterByDesign©.