Start by naming which one you have
Almost every confusing conversation about food reactions comes from four separate conditions being discussed under one word. They differ in what the body is doing, in how fast it happens, in what test finds it, and in whether it can kill you. Sorting them is most of the work.
1. IgE food allergy
A true allergy. The immune system makes IgE antibodies against a food protein, and on re-exposure those antibodies trigger mast cells to release histamine and other mediators within minutes. Hives, swelling, vomiting, wheeze, and at the severe end anaphylaxis, which is a medical emergency.
Fast, reproducible, dose-sensitive at very small amounts, and the only one of the four that is immediately dangerous.
Tested by: skin prick testing and specific IgE blood testing, interpreted alongside history. Confirmed where necessary by supervised oral food challenge.
2. Autoimmune reaction to food
The immune system attacks your own tissue in response to a food. Celiac disease is the definitive example: gluten triggers an immune response that damages the lining of the small intestine. It is not an allergy and it is not a sensitivity, and it carries a long-term trajectory neither of those does.
Reactions can be delayed and diffuse. The damage accumulates whether or not symptoms are dramatic.
Tested by: a specific antibody panel plus biopsy. Covered in full, including the blind spot in the standard test, on the celiac page.
3. Enzyme and transport intolerance
Not immune at all. The body lacks the machinery to process something. Lactose intolerance is missing lactase. Fructose malabsorption is limited transport capacity. Histamine intolerance is proposed to involve reduced activity of the enzyme that degrades dietary histamine, though it is less well characterized than the other two and is often diagnosed loosely.
These are dose-dependent in a way allergy is not. A small amount may cause nothing; a larger amount causes bloating, gas, cramping, diarrhea. That dose relationship is a useful clue.
Tested by: breath testing for lactose and fructose. Histamine intolerance has no validated test.
4. Non-celiac sensitivity, and everything else
The genuine remainder. People who reliably react to a food, in whom allergy, autoimmunity and enzyme deficiency have all been excluded. Non-celiac gluten sensitivity is the best known. Reactions to fermentable carbohydrates, to food chemicals such as salicylates and sulfites, and to additives also sit here.
This category is real and it is poorly understood. Mechanisms are proposed and contested. What is not in doubt is that the people in it are reacting to something.
Tested by: nothing. There is no blood test. Identification is by structured elimination and reintroduction, which is the next tab.
One more thing that looks like a food allergy and is not
Oral allergy syndrome is a cross-reaction: your immune system learned a pollen protein, and a structurally similar protein in raw fruit or vegetables triggers the same recognition. Mouth and lip itching with raw apple and nothing at all with apple pie, because cooking changes the protein shape. It has its own full article, and it is worth knowing about because people often conclude they have developed a dozen new food allergies when they have one pollen sensitization.
The test that is sold everywhere, and what it measures
If you have looked for answers about food reactions, you have been offered an IgG food sensitivity panel. A blood draw, a list of dozens or hundreds of foods, and a colour-coded report ranking your reactivity. They are sold direct to consumers and through many practitioners, and they cost real money.
Here is what needs saying, and this site is saying it about a test common in its own field rather than only about conventional medicine.
IgG antibodies to a food are a marker of exposure. In the case of IgG4 specifically, they are considered a marker of tolerance. Not of reaction. Of the immune system having met the food and decided it is acceptable.
Three professional bodies, the same conclusion
The American Academy of Allergy, Asthma and Immunology states that food-specific IgG testing has never been shown to diagnose food allergy or intolerance, and that IgG frequently reflects normal tolerance.
The European Academy of Allergy and Clinical Immunology issued a Task Force report concluding that testing IgG4 against foods is not recommended as a diagnostic tool, and that its presence indicates exposure and tolerance rather than impending allergy or intolerance.
The Canadian Society of Allergy and Clinical Immunology issued a position statement finding no body of research supporting the test for diagnosing adverse food reactions, and describing food-specific IgG as a marker of exposure and tolerance.
These are not obscure dissenters. They are the specialty bodies for the field the test claims to belong to, and they agree with each other.
Why the results feel accurate anyway
This is the part that explains the popularity, and it is not a story about stupid customers.
If IgG reflects exposure, the panel will flag the foods you eat most. For most people that is wheat, dairy, eggs, and whatever else appears daily. Those are also the foods most likely to be involved in a genuine reaction, simply because you eat them constantly. So the report often names something that really is a problem, by a route that has nothing to do with detecting the problem.
Then acting on the result usually helps, at least at first, because removing several staple foods removes a great deal of processed food along with them. Improvement follows, and it is attributed to the test.
A test can produce useful-seeming results and still not measure what it claims. That is precisely why validation exists, and why "it worked for me" cannot substitute for it.
The cost of a wrong list
The harm is not only the price of the panel. A long list of forbidden foods, most of which are fine, narrows the diet, complicates every meal and social situation, and can push people toward the packaged replacement aisle with everything that carries. In children it raises genuine nutritional and relationship-with-food concerns.
It also does something subtler. It supplies an answer, which ends the search. Someone who accepts an IgG list as their diagnosis stops looking, and the actual cause, which might be celiac disease, a treatable enzyme problem, or something not dietary at all, goes on undetected.
The method that does work, and why nobody sells it
For the fourth category, the sensitivities with no blood test, there is an established approach. It is structured elimination and reintroduction, and it remains the reference standard because it tests the actual question: does this food, in this person, reliably cause this symptom?
It has no product attached, which is most of the reason it is under-promoted relative to a panel.
Why reintroduction is the part that matters
Most people do the first half. They remove foods, feel better or do not, and stop there. That half alone cannot tell you which food was responsible, because several changed at once, and it cannot separate a real effect from the general improvement that comes from eating more carefully and paying attention.
Reintroducing foods one at a time, deliberately, with a gap between each, is what converts a vague improvement into information. It is also the step that feels like going backwards, which is why it gets skipped.
Two things to settle before you start
- ●Rule out celiac disease first, while still eating gluten. This is the single most common sequencing error in the whole topic. Celiac blood tests measure your immune response to gluten, so removing gluten first can produce a false negative in someone who genuinely has the disease. Once removed, getting a reliable answer means eating it again for weeks, which people are understandably unwilling to do. Test before you eliminate, not after.
- ●Do this with a clinician, particularly for a child. Elimination diets narrow nutrition, and the more foods removed the more that matters. Anyone with a history of anaphylaxis, an eating disorder, or significant weight loss should not be running food challenges without supervision, because reintroduction is the point at which a true allergy shows itself.
What this page is not
It is not an elimination protocol, a food list, or instructions to remove anything. Deliberately. Published elimination approaches vary considerably and the right one depends on the person, the symptoms and what has already been excluded. That is a clinical decision, not a web page decision.
What this page is for is the part that comes before: knowing which of the four things you might be dealing with, knowing which tests answer which question, and knowing that the panel most likely to be offered to you measures tolerance rather than reaction.
Questions worth asking
- ●Has celiac disease been excluded with a proper panel, including a total IgA, while I was still eating gluten?
- ●Are my symptoms immediate or delayed, and are they dose-dependent? Those two answers narrow the four categories considerably.
- ●Is there any reason to test for lactose or fructose malabsorption with a breath test before assuming this is immune?
- ●If an IgG panel is being recommended to me, which published validation supports using it to diagnose, given the AAAAI, EAACI and CSACI positions?
Research, Sources & Further Reading
Position Statements on IgG Food Testing
EAACI Task Force Report: "Testing for IgG4 against foods is not recommended as a diagnostic tool"
Food-specific IgG4 reflects a physiological response to exposure and is an indicator of immunological tolerance linked to regulatory T cell activity, not of hypersensitivity.
Allergy, 2008. PMID 18489614
CSACI Position statement on the testing of food-specific IgG
No body of research supports using food-specific IgG to diagnose adverse food reactions; the literature indicates it is a marker of exposure and tolerance.
Allergy, Asthma & Clinical Immunology. PMC3443017
AAAAI position on food-specific IgG testing
Food-specific IgG testing has never been proven to diagnose food allergy or intolerance, and IgG often reflects normal tolerance.
American Academy of Allergy, Asthma and Immunology
"Unproven Diagnostic Tests for Adverse Reactions to Foods"
Review of the tests marketed for food reactions and the evidence behind each.
Journal of Allergy and Clinical Immunology: In Practice, 2017