Understanding Food Tolerance

15 October 2019

“I’m allergic to gluten and diary”, is a common thing I hear from both my clients and just generally in social circles. This whole area can be a very confusing topic, so, I am putting pen to paper and this blog post is designed to help you understand the difference between an allergic food reaction, food sensitivities or intolerances and whether you might benefit from testing.

To help answer this question, it is helpful to understand a little about our immune response. A healthy Immune response is a delicate balance across three areas:

  1. To be defensive
  2. To be restorative
  3. To be tolerant

IgA, IgE, and IgG immune responses refer to immunoglobulins, or “antibodies.”  These antibodies are part of our immune system, and are produced in response to triggers or “antigens”  we come in contact with. Our bodies make antibodies to foreign substances like bacteria and viral cells, but can also respond to foods, dust, dander, and pollen. Antibodies help the body mount an immune system response (“fight”) against foreign invaders. This blog discusses the immunoglobulin production as they relate to food antigens. 

A Food Allergy

Is typically defined as an IgE mediated type I hypersensitivity. The initial exposure to the food antigen causes an immune cell known as a Th2 lymphocyte  to produce a messenger cytokine - IL4 which interacts with B cells to trigger the production of immunoglobulin E (IgE). 

Secreted IgE from the B cells circulates in the blood and binds to a very specific IgE receptor (called an Fc eRI) which is found on the cell membranes of mast cells and basophils. This initial binding of the IgE and the Fc eRI  receptor is called the allergic sensitisation stage, shown here:

In a subsequent exposure to the antigen - same food, the binding of the antigen to the IgE on the surface of the mast cell cross-links the cell-bound IgE and triggers the release of various pharmacologically active substances, namely histamines, leukotrienes, prostaglandins, platelet activating factor and further cytokines which maintains allergic inflammation. The release of these mediators into surrounding tissues causes vasodilation (redness), vasopermeability (edema), mucus secretion, chemotaxis, smooth muscle constriction (bronchoconstriction), and increased pain response. 

Other symptoms can include wheezing, coughing, a runny nose, vomiting, swelling of the lips or tongue, tearing or redness of the eyes, or even a weak pulse and loss of consciousness.

90% of all acute IgE food reactions are triggered by:

  • Dairy
  • Eggs
  • Peanuts
  • Wheat
  • Soy
  • Fish, shellfish
  • Tree nuts- walnuts, cashews, & almonds
  • Corn

*Curr Opin Allergy Clin Immunol. 2009 Aug;9(4):357‐63.

Food Sensitivities 

Food sensitivities, by contrast are a more delayed response and trigger an immune response by producing IgG antibodies. Unlike IgE reactions, IgG antibodies do not directly trigger degranulation of mast cells. IgG has several receptors: the high affinity FcR1 & FcyRIV, and the low affinity FcyRIIB and FCyRIII all expressed on several types of cells - mast cells, basophils, neutrophils and macrophages.

IgG antibodies are expressed approximately 1 month following antigen recognition. Thus, the presence of specific IgG antibodies generally corresponds to a “maturation” of the antibody response. The IgG immunoglobulin class has an exceptionally long half-life in circulation (serum half-lives of IgG ranging from 22 to 96 days) and constitutes about 75% of the total immunoglobulin pool. 

There are four subclasses of numbering 1-4:

  • IgG1 responds to new food antigens.
  • IgG2 and IgG3 react to cell surface of viruses, protozoa, and foods.
  • IgG4 is commonly related to delayed food sensitivity symptoms.

Very interestingly, a specific function of IgG4 is actually to control or “block” IgE and consequently, to regulate anaphylactic reactions and IgE-mediated immunity, as such testing for just IgG4 as many on-line labs offer, is far from an accurate assessment of a food sensitivity.

IgG reactions may not, and generally do not happen immediately, but can take hours to 3 days to show up in your skin or intestines, and cause symptoms related to inflammation like headaches, fatigue, brain fog, or joint pain. People with food intolerance may experience digestive upset like nausea, constipation, or diarrhea, or skin itching and rashes including conditions like eczema and psoriasis. According to a review article titled “Testing for food reactions: the good, bad, and the ugly” by Mullin et al,  symptoms associated with IgG reactions are shown in this table:


IgA Reactions

SIgA is the dominant immunoglobulin secreted across mucosal surfaces, making up a large portion of our immune system, and is often described as our first line of defence. It is critical in developing immune tolerance, often referred to as oral tolerances, and serves to influence other branches of the immune system such as IgG and IgE. 

Exposure to foods, infections, pollen and other environmental antigens is necessary to develop the immune system and oral tolerance, especially true in childhood. 

A number of factors can sabotage this homeostasis, such as oral or gut infections, medications, dietary proteins that have not been fully digested, chronic stress, hormone imbalances.  

When sIgA increases to specific foods, levels may rise initially, and it can be associated with gut-based inflammation, and a loss of “tolerance”.

A Food Intolerance

Is a non-immunological reaction to food. Either due to an inability to break down a food properly (i.e missing enzymes such as lactase to break down lactose and thus resulting in lactose intolerance), an unhealthy microbial environment, or a weakened GI mucous membrane.

Reactions are usually delayed, occurring several hours and sometimes up to several days after eating the offending food. The symptoms caused by these reactions are usually gut symptoms, such as bloating, diarrhoea, constipation and IBS, skin problems such as eczema and joint pain. Examples are:

  • Lactose intolerance (lactase deficiency)

  • Tyramine, histamine (monoamines)

  • MSG, aspartame, sulfites

  • Salicylates

  • Lectins 


To assess for IgG, Complement, IgE, IgG4 + Blocking Potential across 88 food antigens, in serum samples using an indirect ELISA (enzyme linked immunosorbent assay) I use Dunwoody Labs, a sample report shown here:

I also use Cyrex Laboratories, an advanced clinical laboratory specialising in assessing environmentally - induced autoimmunity. Cyrex offers environmental trigger (food and chemicals), barrier permeability and multiple organ self-tissue antibody testing, measuring IgA, IgG & IgM. A sample report shown here:

For children, I often use just an IgA assessment - The Dietary Antigen Specific Secretory IgA (sIgA) test uses saliva to assess one of the earliest responses to 88 food, an example here:

I hope this post has helped better understand the difference between a true allergy and then a sensitivity or intolerance. In my next post I’ll share some areas I work on to support building tolerance.

As always, in health.

Tanya x