The first thing to understand about food sensitivity testing is that it is measuring something completely different from a food allergy test. These two things are often conflated — in conversation, in marketing, and in the questions people bring to clinical consultations. Clarifying the distinction is the necessary starting point for any honest discussion of whether food sensitivity testing is right for a specific situation.
IgE Versus IgG — Two Different Immune Responses
Food allergies are mediated by IgE antibodies — immunoglobulin E. This is the classical allergic response. IgE reactions are immediate, typically occurring within minutes to two hours of exposure. They involve mast cell degranulation, histamine release, and the familiar symptoms of acute allergy: hives, swelling, anaphylaxis in severe cases. IgE food allergies are diagnosed by skin prick testing or specific IgE blood testing. They are generally well-understood, reliably diagnosed, and the clinical guidance around them — avoid the food — is straightforward.
Food sensitivities are mediated by IgG antibodies — immunoglobulin G. This is a delayed immune response. IgG reactions can occur anywhere from two hours to seventy-two hours after exposure, which makes identifying the culprit food through dietary observation almost impossible without systematic elimination. IgG reactions do not involve mast cells or histamine in the same way — they involve a different arm of the immune system that produces chronic, low-grade inflammation rather than acute allergic response.
IgE — Food Allergy
Immediate response — minutes to 2 hours. Mast cell activation, histamine release. Symptoms: hives, swelling, anaphylaxis, acute gut cramping. Diagnosed by skin prick test or IgE blood test. Reliably actionable — avoid the food completely. Well-validated clinically.
IgG — Food Sensitivity
Delayed response — 2 to 72 hours. Low-grade chronic inflammatory response. Symptoms: bloating, fatigue, brain fog, joint pain, skin changes, headache, mood shifts. Diagnosed by IgG antibody blood test. Elimination and reintroduction required to confirm clinical significance.
The conventional medical position on IgG food testing is that it lacks clinical validity — that IgG antibodies simply reflect dietary exposure rather than immune reactivity, and that the presence of an IgG antibody to a food does not mean that food is causing a problem. This is not entirely wrong. But it is not the complete picture.
IgG antibodies do reflect exposure. A person who eats a lot of eggs will develop IgG antibodies to egg protein. Most of the time, these antibodies represent immune tolerance — the immune system recognising a familiar food without mounting an inflammatory response. In this context, IgG testing does not diagnose a meaningful sensitivity.
However — and this is the clinically important nuance — in a person with gut barrier compromise, the situation is different. When the tight junctions of the gut lining are leaky, partially digested food proteins cross into systemic circulation in a form the immune system does not recognise as self or as a familiar, safe antigen. The immune system responds to these foreign proteins with IgG antibody production that is associated with inflammation rather than tolerance. In this context, an elevated IgG response to a food does reflect a genuine immune reaction — not to the food itself, but to the abnormal exposure created by the compromised barrier.
The argument that IgG testing is meaningless because IgG antibodies reflect exposure rather than sensitivity misses a critical clinical variable: gut barrier integrity. In a person with leaky gut, elevated IgG to foods is not a marker of normal exposure — it is a marker of immune activation driven by abnormal exposure through a damaged barrier.
What IgG Testing Is and Is Not Useful For
IgG food sensitivity testing is most useful in the following clinical contexts:
Chronic inflammatory presentations with no identified cause. Persistent joint pain, chronic skin conditions, recurring headaches, unexplained fatigue, and mood instability that have not responded to standard investigation may have a food-driven inflammatory component. IgG testing, interpreted in the context of gut barrier markers, can identify whether specific foods are contributing to the inflammatory load.
Gut symptoms with no clearly identified mechanism. When the GI-MAP has ruled out specific pathogens and SIBO has been assessed or treated, IgG testing can identify whether food antigens are maintaining gut wall inflammation and preventing healing. Continuing to eat foods that are generating an immune response in a person with gut barrier compromise is like trying to repair a wound while repeatedly reopening it.
Autoimmune conditions where dietary triggers are clinically relevant. The relationship between food antigens and autoimmune activity — particularly through molecular mimicry, where immune responses to food proteins cross-react with self-tissue — is well-established for gluten and thyroid tissue in Hashimoto’s, and for various foods and joint tissue in reactive arthritis. IgG testing, combined with specific antibody testing for the relevant autoimmune process, can inform dietary management in these conditions.
Identifying the most inflammatory foods before an elimination diet. Rather than removing all common allergens simultaneously — a disruptive and socially demanding process — IgG testing can narrow the elimination to the specific foods generating the highest response, making the protocol more targeted and more manageable.
IgG testing is not useful as a standalone diagnostic tool without clinical context. A list of elevated IgG reactions without understanding gut barrier status, without cross-referencing with symptoms, and without a proper elimination and reintroduction protocol to confirm clinical significance is of limited value. The test is one piece of information, not a diagnosis.
The Gut Barrier Artefact Problem
One of the most important and least discussed aspects of IgG food testing is what happens when barrier compromise is severe. When zonulin is significantly elevated — indicating widespread tight junction disruption — a person may show elevated IgG responses to a very large number of foods: fifteen, twenty, sometimes more. This broad reactivity pattern is not evidence that the person is genuinely sensitive to all those foods. It is evidence that their gut barrier is so compromised that virtually any dietary protein is generating an immune response through abnormal exposure.
In this clinical picture, eliminating twenty foods simultaneously is not the right intervention. It is also not practical or sustainable. The right intervention is gut barrier repair — addressing the upstream cause of the abnormal permeability — while making targeted reductions in the highest-response foods. As the barrier heals, the broad IgG reactivity typically narrows dramatically. Foods that generated a strong response in a leaky gut state may generate no response at all once barrier integrity is restored.
This is why the GI-MAP and IgG food sensitivity panel are read together in the TDG programme. The GI-MAP’s zonulin and secretory IgA markers establish barrier integrity. The IgG panel is then interpreted in that context — broad reactivity with high zonulin is a different clinical picture from narrow, specific reactivity with a normal zonulin level.
IgA Food Sensitivity — The Additional Layer
Some food sensitivity panels also measure IgA antibodies — secretory immunoglobulin A. This is the primary antibody of mucosal immunity, present in the gut lining, saliva, and respiratory tract. IgA reactions to foods are associated with mucosal inflammation rather than systemic immune activation — they reflect a gut-level response rather than a systemic one.
Elevated IgA to gluten — anti-gliadin IgA — is the most clinically significant finding in this category. It can be elevated in people who are not coeliac but who have genuine non-coeliac gluten sensitivity, representing a mucosal immune response to gliadin that drives gut inflammation without the villous atrophy characteristic of coeliac disease. IgA anti-gliadin testing can identify this population — people who benefit from gluten elimination but who would test negative on standard coeliac serology.
Elimination and Reintroduction — The Only Way to Confirm Clinical Significance
An IgG result identifies which foods the immune system has mounted a response to. It does not, by itself, tell you whether removing those foods will change how you feel. The only way to establish clinical significance is through systematic elimination followed by structured reintroduction.
The protocol: remove the identified high-reactivity foods completely for a minimum of four to six weeks. Assess symptoms at baseline and at the end of the elimination phase. Reintroduce foods one at a time, eating a significant amount of each food on the reintroduction day and monitoring for symptoms over the following seventy-two hours before moving to the next food. Foods that consistently produce symptoms on reintroduction are confirmed sensitivities. Foods that produce no response are likely safe to return.
This process takes time and discipline, but it produces genuinely useful clinical information that the test alone cannot provide. The combination — IgG testing to identify the candidates, elimination to create a symptom-free baseline, reintroduction to confirm — is the complete diagnostic sequence.
Consider it if: You have chronic symptoms — bloating, fatigue, brain fog, joint pain, skin conditions, headaches — that are consistent but not explained by standard testing. You suspect food is involved but cannot identify a clear pattern through observation. You have confirmed gut barrier compromise on GI-MAP and want to identify which foods are maintaining the inflammatory cycle.
Do not expect it to: Diagnose IgE allergies (use specific IgE testing for that). Identify every food that could ever cause a problem. Replace gut barrier repair as the primary intervention when zonulin is significantly elevated. Provide a definitive answer without elimination and reintroduction to confirm clinical significance.
The TDG approach: Food sensitivity panel is the fifth test in the five-test programme — read last, after the GI-MAP has established gut barrier status, because barrier status determines how the IgG results should be interpreted.
The polarised debate around IgG food testing — either it’s the answer to everything or it’s completely useless — is not a debate about the science. It is a debate about context. In a clinical framework that reads IgG results alongside gut barrier markers, interprets broad reactivity as a barrier artefact rather than genuine sensitivity, and confirms findings through proper elimination and reintroduction, food sensitivity testing is a genuinely useful clinical tool. Used in isolation, without that framework, it produces lists of foods to avoid that are often more disruptive than therapeutic.
Test, don’t guess — and interpret the test within its proper context.