Food allergies, sensitivities, and intolerances can be confusing for practitioners and patients alike. After all, these words are often used interchangeably despite having different mechanisms of action. It’s important for clinicians to understand how these terms differ, how adverse food reactions may contribute to a client’s symptoms, and how to assimilate this knowledge into an integrative and functional nutrition care plan.
What are Adverse Food Reactions?
Food allergies, sensitivities, and intolerances all exist under the adverse food reactions (AFR) umbrella, and they are broadly classified as toxic or non-toxic. Toxic reactions occur in anyone who consumes contaminated food (for example, bacterial food poisoning). Non-toxic reactions occur in susceptible people and are further categorized into immunologic (food allergies and food sensitivities) or non-immunologic (food intolerances) (1).
Food Allergy
A food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly after exposure to a particular food antigen (2). Food allergies may be IgE-mediated, non-IgE-mediated, or mixed IgE/non-IgE-mediated, with each type involving different immune mechanisms and clinical presentations.
IgE-Mediated Food Allergy
IgE-mediated reactions are the most recognized form of food allergy (3). Symptoms typically occur within minutes to two hours after eating the offending food and may include (3,4):
- Hives
- Itching
- Swelling
- Wheezing or difficulty breathing
- Vomiting, diarrhea, bloody stool
- Anaphylaxis
Even very small amounts of the food can trigger a reaction. Although there have been greater than 160 foods known to cause IgE-mediated food allergy reactions, food allergy labeling legislation has identified the top nine food allergens, which are responsible for more than 90 percent of food allergy reactions (7,8):
- Milk
- Eggs
- Fish
- Shellfish
- Tree nuts
- Peanuts
- Wheat
- Soy
- Sesame
Non-IgE-Mediated Food Allergy
Non-IgE-mediated food allergies can involve a variety of inflammatory mediators including antigen-specific T cells and cytokines (12).
Examples include:
- Food protein-induced enterocolitis syndrome (FPIES)
- Food protein-induced allergic proctocolitis (FPIAP)
- Food protein-induced enteropathy (FPE)
These conditions primarily affect infants and children causing gastrointestinal tract symptoms including severe vomiting, diarrhea (sometimes containing blood and mucus), and failure to thrive (12).
Mixed IgE/Non-IgE Disorders
Mixed IgE/non-IgE-mediated food allergies are immune-mediated adverse food reactions characterized by the involvement of both allergen-specific IgE antibodies and cellular (T-cell-mediated) immune mechanisms (6). Examples include:
- Eosinophilic esophagitis (EoE)
- Atopic dermatitis with food allergy in certain people
- Other eosinophilic gastrointestinal disorders (EGIDs)
Clinical manifestations may include both acute and delayed symptoms affecting the skin, gastrointestinal tract, and other organ systems.
Food Sensitivities
A food sensitivity is a non-IgE-mediated adverse food reaction that involves the immune system but is not a true allergic reaction (4). Food sensitivities result when the body has difficulty digesting substances, such as histamines or food additives. The mechanism of action is complex and involves immune system activation via IgG or IgA antibodies, mediator release, complement activation, or other mechanism. T and B cells, neutrophils, basophils, macrophages, eosinophils, and cytokines may be involved and reactions can be immediate to delayed (4).
Common triggers of food sensitivities include (4):
- Wheat
- Soy
- Caffeine
- Alcohol
- Food additives
Food sensitivity reactions can result from small amounts of the offending food or from cumulative exposure over time. Symptoms include digestive distress, neurological issues, skin rashes, runny nose, and autoimmune flares (4).
Food Intolerances
Food intolerances do not involve the immune system. Rather, they are the result of impaired digestion or absorption of certain foods or their components, for example (4):
- Enzyme deficiencies (lactase deficiency)
- Carbohydrate malabsorption (fructose intolerance)
- Pharmacologic compounds (caffeine)
- Food additives (sulfites, MSG, artificial colors)
- Histamine intolerance
Food intolerances are generally dose dependent, meaning many people can tolerate small amounts of the offending food. Food intolerance symptoms may take hours to days to appear and can include digestive discomfort (bloating, nausea, constipation, gas, abdominal pain, heartburn), as well as systemic symptoms such as fatigue and joint pain (4).
Testing for Adverse Food Reactions
There are a wide variety of testing options for adverse food reactions. IgE-mediated food allergy testing is straightforward and both serum and skin prick testing are effective (9). One testing area that continues to generate confusion is IgG food sensitivity testing.
Although numerous commercial tests measure food-specific IgG antibodies, major professional organizations including the American Academy of Allergy, Asthma, and Immunology (AAAI), the European Academy of Allergy and Clinical Immunology (EAACI), and the Canadian Society of Allergy and Clinical Immunology (CSACI) do not recommend IgG testing for diagnosing food allergies, sensitivities, or intolerances (10).
Current evidence suggests that IgG antibodies often represent normal exposure and immune tolerance to foods, rather than true adverse food reactions. While some integrative clinicians use IgG testing as one piece of the clinical picture, results should never be interpreted in isolation or used as the sole basis for long-term food elimination.
When it comes to food sensitivity testing, a clinician-guided food elimination with systematic reintroduction remains the most reliable method for identifying triggers. The table below provides a snapshot of possible testing options for adverse food reactions:
| Adverse Food Reaction | Testing Options |
| Food allergy |
|
| Food sensitivity |
|
| Food Intolerance |
|
Addressing Adverse Food Reactions
The “A” in the IFN Academy signature STAIN© model represents adverse food reactions. AFRs are one root cause of negative symptoms and addressing them promptly can often provide rapid symptom relief while the other areas of STAIN© are being investigated.
One exciting area of research is the role of the gut microbiome in maintaining oral tolerance or the immune system’s ability to recognize food proteins as harmless (11). Several factors may impair this process, including:
- Antibiotic exposure
- Inflammatory dietary pattern
- Low dietary fiber intake
- Gut dysbiosis
- Reduced microbial diversity
- Altered intestinal barrier function
- Environmental exposures
These findings reinforce the importance of supporting overall gastrointestinal health through an individualized nutrition and lifestyle approach. Integrative and functional nutritionists often start by prescribing a personalized elimination diet in conjunction with the 5-R protocol to not only uncover and address adverse food reactions, but to repair the gut lining and rebalance the gut microbiome.
As integrative and functional nutritionists, rather than simply identifying foods to eliminate, we seek to understand why adverse food reactions may have developed in the first place. We address the underlying contributors with a comprehensive, whole-person plan.
Track 4 covers therapeutic elimination diets for many different adverse food reactions. Be sure to sign up for your IFN Academy training today to learn how to employ an integrative and functional nutrition approach with your clients.
By: Kellie Blake, RDN, LD, IFNCP
References:
- Tedner SG, Asarnoj A, Thulin H, Westman M, Konradsen JR, Nilsson C. Food allergy and hypersensitivity reactions in children and adults—a review. J Intern Med. 2022; 291: 283–302.
- U.S. Food and Drug Administration. Food Allergies | FDA. Accessed July 7, 2026.
- Waserman S, Bégin P, Watson W. IgE-mediated food allergy. Allergy Asthma Clin Immunol. 2018;14(Suppl 2):55. Published 2018 Sep 12. doi:10.1186/s13223-018-0284-3
- Mousavi Khaneghah, A., & Mostashari, P. (2025). Decoding food reactions: a detailed exploration of food allergies vs. intolerances and sensitivities. Critical Reviews in Food Science and Nutrition, 65(14), 2669–2713. https://doi.org/10.1080/10408398.2024.2349740
- Nowak-Węgrzyn A, et al. Non–IgE-mediated gastrointestinal food allergyJournal of Allergy and Clinical Immunology, 135, 1114-1124.
- Calvani M, Anania C, Cuomo B, et al. Non-IgE- or Mixed IgE/Non-IgE-Mediated Gastrointestinal Food Allergies in the First Years of Life: Old and New Tools for Diagnosis. Nutrients. 2021;13(1):226. Published 2021 Jan 14. doi:10.3390/nu13010226
- Food Allergies. U.S. Food and Drug Administration. Food Allergies | FDA Accessed 05/28/2021.
- Food and Drug Administration Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) | FDA Accessed 05/28/2021.
- Mullin, G. et al. (2010). Testing for Food Reactions: The Good, the Bad, and the Ugly. Nutrition in Clinical Practice Volume 25 Number 2 April 2010 192-198.
- American Academy of Allergy, Asthma, and Immunology. The myth of IgG food panel testing | AAAAI. Accessed July 7, 2026.
- Suárez LJ, Arboleda S, Angelov N and Arce RM (2021) Oral Versus Gastrointestinal Mucosal Immune Niches in Homeostasis and Allostasis. Front. Immunol. 12:705206. doi: 10.3389/fimmu.2021.705206
- Zhang S, Sicherer S, Berin MC, Agyemang A. Pathophysiology of Non-IgE-Mediated Food Allergy. Immunotargets Ther. 2021;10:431-446. Published 2021 Dec 29. doi:10.2147/ITT.S284821
Food allergies, sensitivities, and intolerances can be confusing for practitioners and patients alike. After all, these words are often used interchangeably despite having different mechanisms of action. It’s important for clinicians to understand how these terms differ, how adverse food reactions may contribute to a client’s symptoms, and how to assimilate this knowledge into an integrative and functional nutrition care plan.
What are Adverse Food Reactions?
Food allergies, sensitivities, and intolerances all exist under the adverse food reactions (AFR) umbrella, and they are broadly classified as toxic or non-toxic. Toxic reactions occur in anyone who consumes contaminated food (for example, bacterial food poisoning). Non-toxic reactions occur in susceptible people and are further categorized into immunologic (food allergies and food sensitivities) or non-immunologic (food intolerances) (1).
Food Allergy
A food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly after exposure to a particular food antigen (2). Food allergies may be IgE-mediated, non-IgE-mediated, or mixed IgE/non-IgE-mediated, with each type involving different immune mechanisms and clinical presentations.
IgE-Mediated Food Allergy
IgE-mediated reactions are the most recognized form of food allergy (3). Symptoms typically occur within minutes to two hours after eating the offending food and may include (3,4):
- Hives
- Itching
- Swelling
- Wheezing or difficulty breathing
- Vomiting, diarrhea, bloody stool
- Anaphylaxis
Even very small amounts of the food can trigger a reaction. Although there have been greater than 160 foods known to cause IgE-mediated food allergy reactions, food allergy labeling legislation has identified the top nine food allergens, which are responsible for more than 90 percent of food allergy reactions (7,8):
- Milk
- Eggs
- Fish
- Shellfish
- Tree nuts
- Peanuts
- Wheat
- Soy
- Sesame
Non-IgE-Mediated Food Allergy
Non-IgE-mediated food allergies can involve a variety of inflammatory mediators including antigen-specific T cells and cytokines (12).
Examples include:
- Food protein-induced enterocolitis syndrome (FPIES)
- Food protein-induced allergic proctocolitis (FPIAP)
- Food protein-induced enteropathy (FPE)
These conditions primarily affect infants and children causing gastrointestinal tract symptoms including severe vomiting, diarrhea (sometimes containing blood and mucus), and failure to thrive (12).
Mixed IgE/Non-IgE Disorders
Mixed IgE/non-IgE-mediated food allergies are immune-mediated adverse food reactions characterized by the involvement of both allergen-specific IgE antibodies and cellular (T-cell-mediated) immune mechanisms (6). Examples include:
- Eosinophilic esophagitis (EoE)
- Atopic dermatitis with food allergy in certain people
- Other eosinophilic gastrointestinal disorders (EGIDs)
Clinical manifestations may include both acute and delayed symptoms affecting the skin, gastrointestinal tract, and other organ systems.
Food Sensitivities
A food sensitivity is a non-IgE-mediated adverse food reaction that involves the immune system but is not a true allergic reaction (4). Food sensitivities result when the body has difficulty digesting substances, such as histamines or food additives. The mechanism of action is complex and involves immune system activation via IgG or IgA antibodies, mediator release, complement activation, or other mechanism. T and B cells, neutrophils, basophils, macrophages, eosinophils, and cytokines may be involved and reactions can be immediate to delayed (4).
Common triggers of food sensitivities include (4):
- Wheat
- Soy
- Caffeine
- Alcohol
- Food additives
Food sensitivity reactions can result from small amounts of the offending food or from cumulative exposure over time. Symptoms include digestive distress, neurological issues, skin rashes, runny nose, and autoimmune flares (4).
Food Intolerances
Food intolerances do not involve the immune system. Rather, they are the result of impaired digestion or absorption of certain foods or their components, for example (4):
- Enzyme deficiencies (lactase deficiency)
- Carbohydrate malabsorption (fructose intolerance)
- Pharmacologic compounds (caffeine)
- Food additives (sulfites, MSG, artificial colors)
- Histamine intolerance
Food intolerances are generally dose dependent, meaning many people can tolerate small amounts of the offending food. Food intolerance symptoms may take hours to days to appear and can include digestive discomfort (bloating, nausea, constipation, gas, abdominal pain, heartburn), as well as systemic symptoms such as fatigue and joint pain (4).
Testing for Adverse Food Reactions
There are a wide variety of testing options for adverse food reactions. IgE-mediated food allergy testing is straightforward and both serum and skin prick testing are effective (9). One testing area that continues to generate confusion is IgG food sensitivity testing.
Although numerous commercial tests measure food-specific IgG antibodies, major professional organizations including the American Academy of Allergy, Asthma, and Immunology (AAAI), the European Academy of Allergy and Clinical Immunology (EAACI), and the Canadian Society of Allergy and Clinical Immunology (CSACI) do not recommend IgG testing for diagnosing food allergies, sensitivities, or intolerances (10).
Current evidence suggests that IgG antibodies often represent normal exposure and immune tolerance to foods, rather than true adverse food reactions. While some integrative clinicians use IgG testing as one piece of the clinical picture, results should never be interpreted in isolation or used as the sole basis for long-term food elimination.
When it comes to food sensitivity testing, a clinician-guided food elimination with systematic reintroduction remains the most reliable method for identifying triggers. The table below provides a snapshot of possible testing options for adverse food reactions:
| Adverse Food Reaction | Testing Options |
| Food allergy |
|
| Food sensitivity |
|
| Food Intolerance |
|
Addressing Adverse Food Reactions
The “A” in the IFN Academy signature STAIN© model represents adverse food reactions. AFRs are one root cause of negative symptoms and addressing them promptly can often provide rapid symptom relief while the other areas of STAIN© are being investigated.
One exciting area of research is the role of the gut microbiome in maintaining oral tolerance or the immune system’s ability to recognize food proteins as harmless (11). Several factors may impair this process, including:
- Antibiotic exposure
- Inflammatory dietary pattern
- Low dietary fiber intake
- Gut dysbiosis
- Reduced microbial diversity
- Altered intestinal barrier function
- Environmental exposures
These findings reinforce the importance of supporting overall gastrointestinal health through an individualized nutrition and lifestyle approach. Integrative and functional nutritionists often start by prescribing a personalized elimination diet in conjunction with the 5-R protocol to not only uncover and address adverse food reactions, but to repair the gut lining and rebalance the gut microbiome.
As integrative and functional nutritionists, rather than simply identifying foods to eliminate, we seek to understand why adverse food reactions may have developed in the first place. We address the underlying contributors with a comprehensive, whole-person plan.
Track 4 covers therapeutic elimination diets for many different adverse food reactions. Be sure to sign up for your IFN Academy training today to learn how to employ an integrative and functional nutrition approach with your clients.
By: Kellie Blake, RDN, LD, IFNCP
References:
- Tedner SG, Asarnoj A, Thulin H, Westman M, Konradsen JR, Nilsson C. Food allergy and hypersensitivity reactions in children and adults—a review. J Intern Med. 2022; 291: 283–302.
- U.S. Food and Drug Administration. Food Allergies | FDA. Accessed July 7, 2026.
- Waserman S, Bégin P, Watson W. IgE-mediated food allergy. Allergy Asthma Clin Immunol. 2018;14(Suppl 2):55. Published 2018 Sep 12. doi:10.1186/s13223-018-0284-3
- Mousavi Khaneghah, A., & Mostashari, P. (2025). Decoding food reactions: a detailed exploration of food allergies vs. intolerances and sensitivities. Critical Reviews in Food Science and Nutrition, 65(14), 2669–2713. https://doi.org/10.1080/10408398.2024.2349740
- Nowak-Węgrzyn A, et al. Non–IgE-mediated gastrointestinal food allergyJournal of Allergy and Clinical Immunology, 135, 1114-1124.
- Calvani M, Anania C, Cuomo B, et al. Non-IgE- or Mixed IgE/Non-IgE-Mediated Gastrointestinal Food Allergies in the First Years of Life: Old and New Tools for Diagnosis. Nutrients. 2021;13(1):226. Published 2021 Jan 14. doi:10.3390/nu13010226
- Food Allergies. U.S. Food and Drug Administration. Food Allergies | FDA Accessed 05/28/2021.
- Food and Drug Administration Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) | FDA Accessed 05/28/2021.
- Mullin, G. et al. (2010). Testing for Food Reactions: The Good, the Bad, and the Ugly. Nutrition in Clinical Practice Volume 25 Number 2 April 2010 192-198.
- American Academy of Allergy, Asthma, and Immunology. The myth of IgG food panel testing | AAAAI. Accessed July 7, 2026.
- Suárez LJ, Arboleda S, Angelov N and Arce RM (2021) Oral Versus Gastrointestinal Mucosal Immune Niches in Homeostasis and Allostasis. Front. Immunol. 12:705206. doi: 10.3389/fimmu.2021.705206
- Zhang S, Sicherer S, Berin MC, Agyemang A. Pathophysiology of Non-IgE-Mediated Food Allergy. Immunotargets Ther. 2021;10:431-446. Published 2021 Dec 29. doi:10.2147/ITT.S284821