Addressing Adverse Food Reactions: A Functional Nutrition Approach

May 15th, 2023

Food allergies and intolerances can be confusing for practitioners and patients alike. After all, these words are often used interchangeably despite having very different meanings. It’s important for clinicians to understand how these terms differ, how food allergies and/or intolerances may contribute to a clients’ symptoms, and how to incorporate this knowledge into the nutrition care plan for healing.

Food allergies and food intolerances are both considered adverse food reactions that seem to be on the rise in the U.S. As described in one observational study in the journal Pediatric Allergy and Immunology, between 2005 and 2014, there was a 214 percent increase overall in emergency room visits for food-induced anaphylaxis in children under the age of 18 (1). In addition, as reported in a cross-sectional survey in JAMA Network Open, 10.8 percent of U.S. adults had been diagnosed with at least one food allergy with a whopping 19 percent reporting a self-diagnosed food allergy (2). While the exact cause is likely multifactorial, the increase in adverse food reactions may in part, be related to less microbial exposure and the alterations to the gut microbiome that occur with the standard Western-type diet.

What are Adverse Food Reactions? 

Adverse food reactions can be classified as toxic or non-toxic and then further divided into food intolerances or food allergies based on whether the immune system is involved (3). According to the National Institute of Allergy and Infectious Diseases, a food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a specific food (3). While the innate immune system can mediate immune reactions against certain food components, the adaptive immune system is responsible for the majority of immune-mediated food reactions. These types of reactions can be sorted into four categories:

  • Type I reactions, the most common and serious of the immune-mediated reactions, are IgE-mediated meaning the immunoglobulin antibody IgE is formed against a specific food. These reactions occur rapidly with exposure to even small amounts of the food, last for a brief period of time, and involve mast cell activation.
  • Type II and III reactions involve IgG mediation. IgG is the most abundant antibody in the body and is not only responsible for these types of reactions, but is also suspected as a contributor to increased intestinal permeability leading to food allergy. Repeated exposure to an antigen creates hypersensitivities and delayed reactions to foods related to IgG response. Type II and III reactions can take days to develop, can last for longer periods of time, and are dose-dependent, meaning small amounts of the food may not illicit a response. IgG can be classified into four categories (1 through 4). IgG1 and IgG4 are associated with immune responses to foods.
  • Type IV reactions are T-cell mediated and can cause damage to the gastrointestinal mucosal lining such as in celiac disease. In addition, type IV reactions could be implicated in the development of enterocolitis from certain food proteins, which kick starts the innate immune system to get involved such as in nonceliac wheat sensitivity.

Food intolerances, on the other hand, do not involve the immune system. Rather, there may be an enzyme defect or a reaction to a specific substance in a particular food. Good examples include lactose or fructose intolerance or the non-allergic hypersensitivity to food additives and components like red and yellow dyes and sulfites.

What are the major food allergens?

While there have been greater than 160 foods known to cause food allergy reactions, the U.S. Congress passed the Food Allergen Labeling and Consumer Protection Act of 2004 to identify the top eight food allergens, which are responsible for more than 90 percent of food allergy reactions, and include (4,5):

  • Milk
  • Eggs
  • Fish
  • Shellfish
  • Tree nuts
  • Peanuts
  • Wheat
  • Soy

More recently in April of 2021, the Food Allergy Safety, Treatment, Education and Research Act named sesame the ninth major food allergen. Food labeling laws require that all major food allergens be identified on product packaging. The most current labeling law will go into effect for sesame in January of 2023.

What symptoms are associated with Adverse Food Reactions?

Type I reactions can cause serious symptoms such as anaphylaxis and even death, but also elicit hives, asthma, diarrhea, vomiting and a runny nose.  Type II and III reactions are often delayed, taking up to three days to develop. Symptoms can exist on a spectrum with a systemic effect impacting the brain, lungs, digestive tract, skin, and joints. Common indications of type II and III reactions include fatigue, bloating, diarrhea, joint pain, stiffness and swelling, skin rashes and hives and behavioral or memory problems.  Type IV reactions may have no symptoms at all, but can significantly impact the gastrointestinal tract and/or have a systemic effect. Food intolerance symptoms also exist on a spectrum and often include gastrointestinal distress and skin manifestations.

Testing for Adverse Food Reactions

For IgE-mediated allergies, skin prick testing, food challenge testing and food sensitivity testing are all available methods.  Testing for IgE in the serum and skin has been shown to be an effective option (6). Food challenge testing is also effective, but can be time-consuming and patients with severe allergies may experience an anaphylactic reaction, thus medical supervision is necessary.

IgG-mediated reactions are more difficult to diagnose. A variety of food sensitivity testing kits are available, but there is no standardization in labs and false positives and false negatives can be common (6). There are some helpful options, but the jury is still out on the validity of IgG testing.

For T-cell mediated reactions, small intestine biopsy can diagnose celiac disease, but serum and genetic testing are available as well.

Food intolerance testing may include food challenge, breath and/or stool testing.


Using the STAIN model to address Adverse Food Reactions

STAIN is an acronym developed by the founders of the Integrative and Functional Nutrition Academy (IFNA) to help clinicians structure their root cause analysis. As integrative providers, it’s important to understand the many system(s) imbalances that may be contributing to a client’s symptoms. STAIN addresses five important contributors of disease symptoms:

  • Stress
  • Toxins
  • Adverse Food Reactions
  • Infections
  • Nutritional Imbalances










While clients experience imbalances in many, or even all of these areas, addressing adverse food reactions promptly can often provide rapid symptom relief while the other areas of STAIN are being investigated and addressed.  A therapeutic elimination diet with a structured reintroduction food plan is considered to be the gold standard when uncovering specific foods and additives that may be contributing to negative symptoms.

Determining the best type of elimination diet depends on the findings of a functional nutrition assessment that is personalized to the patients’ needs.  For example, an autoimmune diet protocol may be best suited for one patient, while another patient may require a histamine- restricted diet.  Functionally-trained practitioners often implement the elimination diet in conjunction with the 5-R protocol as a way to not only uncover and address adverse food reactions, but to repair the gut lining and rebalance the gut microbiome.

When it’s time to reintroduce eliminated foods, each food is methodically added back in its pure form and symptoms are carefully monitored. Trigger foods are then once again eliminated as part of the maintenance therapeutic meal plan, which will likely need to be fine-tuned over time.

Helping clients navigate the sometimes-confusing world of adverse food reactions involves learning how to evaluate the entire clinical picture. While food sensitivity testing is available and can be an adjunct, it’s important to remember these tests should not simply be taken at face value and are not a substitute for a thorough clinical assessment and integrated functional nutrition care plan.

To learn more about a functional nutrition approach to addressing adverse food reactions, register for your IFNA training today!

You’ll see that Track 4 covers therapeutic diets for all different types of adverse food reactions, allergies and food sensitivities, so be sure to check it out!

by Kellie Blake RDN, LD, IFNCP



  1. Motosue, M. S. et al. (2018). National trends in emergency department visits and hospitalizations for food-induced anaphylaxis in US children. Pediatric allergy and immunology: official publication of the European Society of Pediatric Allergy and Immunology29(5), 538–544.
  2. Gupta, R. S. et al. (2019). Prevalence and Severity of Food Allergies Among US Adults. JAMA network open2(1), e185630.
  3. Valenta, R. et al. (2015). Food allergies: the basics. Gastroenterology148(6), 1120–31.e4.
  4. Food Allergies. U.S. Food and Drug Administration. Food Allergies | FDA Accessed 05/28/2021.
  5. S Food and Drug Administration Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA) | FDA Accessed 05/28/2021.
  6. 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.