IgG Food Sensitivity Tests: What a Positive Result Really Means, and the Tests That Can Find a Food Problem
Home kits measure IgG antibodies to dozens or hundreds of foods. Allergy societies in Europe, the US and Canada say those antibodies mostly show you have eaten a food, not that it harms you. Two small diet trials are the strongest case for the tests.
By Kymata Health Editorial Published Last checked
Key takeaways
From 7 sources- A European allergy task force concluded that food-specific IgG4 reflects repeated exposure and tolerance, not allergy or intolerance, and said the test should not be done for food complaints1.
- The Canadian allergy society said positive IgG results are expected in healthy adults and children, and that the tests often cost $400 to $7002.
- Someone with a true IgE food allergy may have no raised IgG to that food, so a clean IgG panel can wrongly suggest a dangerous food is safe2.
- In the best-known diet trial, 150 people with IBS cut foods flagged by IgG or a sham list; the IgG diet cut symptom scores 10% more at 12 weeks4.
- Lactose intolerance has a real test: a hydrogen breath test after a measured lactose drink6.
What this article covers
2 evidence profilesThe evidence, graded
Pulled from the trial tables in our evidence profiles. Grades follow our evidence-grading policy.
Graded findings
1 row- CGrade CBreath hydrogen and symptoms after a 25 g lactose loadImproved Symptom scores and breath hydrogen were lower with lactase than placebo; cumulative breath hydrogen over 3 hours fell by 55%.Lactase enzyme · Crossover RCT · n=47 · 2021 · PMID 33490624
Safety at a glance
From our Lactase enzyme evidence profilePublished interactions and cautions only. Each one is cited on our Lactase enzyme evidence profile, with its own numbered sources.
Who should be careful
- Milk allergy
- Lactase only breaks down milk sugar; it does nothing for milk allergy, which is an immune reaction to milk.
- Infants
- Evidence in infant colic is mixed and partly at high risk of bias, so use in babies is a question for their clinician.
- Persistent digestive symptoms
- Lactose intolerance can follow injury to the small intestine, which may need its own treatment; ongoing symptoms deserve assessment.
- Pregnancy and breastfeeding
- NIDDK advises checking with a doctor before using lactase products and notes that some people, such as young children and pregnant and breastfeeding women, may not be able to use them. No trial cited here studied pregnant or breastfeeding women.
What the kit actually measures
Food sensitivity panels use a blood sample to measure IgG or IgG4 antibodies against long lists of foods, often hundreds at a time1. The European Academy of Allergy and Clinical Immunology task force noted that many people test positive with no matching symptoms, and that there are no controlled studies showing the test diagnoses food allergy1.
Its conclusion: IgG4 against a food is a normal immune response to eating it, and may even mark tolerance, so testing is irrelevant to working up food allergy or intolerance1. The Canadian Society of Allergy and Clinical Immunology reached the same view in 2012, noting that the American academy (AAAAI) also backed the European position2.
A 2018 review of unproven food tests put serum IgG and IgG4 alongside hair analysis and applied kinesiology: the lab method may be valid, but no studies tie the result to disease3.
Why almost everyone gets a list of “problem” foods
If IgG rises with exposure, the foods you eat most often are the ones most likely to light up12. So a long list of flagged foods may say more about your usual diet than about what disagrees with you. The Canadian statement warned that acting on these results leads to unnecessary diet restrictions, and that cutting dairy, wheat or eggs from a child’s diet risks poor growth and malnutrition2.
The opposite error matters too. A person with a real IgE allergy, the kind that can cause anaphylaxis, may not have raised IgG to that food, and could be wrongly told to eat it again2.
The two trials that test-makers point to
The strongest evidence for IgG-guided diets comes from two small randomized trials. In a 2004 UK trial, 150 outpatients with irritable bowel syndrome followed either a diet cutting all foods with raised IgG or a sham diet cutting the same number of other foods for 3 months4. Symptom scores fell 10% more on the IgG diet, and 26% more in people who stuck to it fully4. The authors called the approach worth further research, not proven4.
A 2010 crossover trial in 30 people with migraine without aura compared 6 weeks of eliminating IgG-flagged foods with 6 weeks of eating them5. Headache days fell from an average of 10.5 to 7.5 during the elimination period compared with baseline5.
Both trials are small and short, and neither shows that IgG identifies the foods that cause symptoms rather than simply nudging people toward a more restricted diet. That is why the allergy societies’ position has not changed123.
Tests that can identify a real food problem
Different food reactions need different tests:
- Lactose intolerance: a hydrogen breath test measures breath hydrogen every 30 minutes over a few hours after a lactose drink6. If it is confirmed, lactase tablets cut breath hydrogen by 55% and eased symptoms in a 47-person crossover trial; see our lactase page7.
- Food allergy: the kind that can cause anaphylaxis is IgE-mediated, and IgG panels cannot rule it out2. Allergy testing belongs with an allergist.
- Gut symptoms with no clear trigger: lactose intolerance can look like IBS, celiac disease, inflammatory bowel disease or bacterial overgrowth, so persistent symptoms are worth a clinician’s look6.
- General blood work: if you want lab tests you can order yourself, see how we rate blood-test services and our guide to ordering your own blood work.
Where supplements fit
Lactase is the one supplement on this page with trials behind it for a food-specific problem, and only once lactose intolerance is established7. Probiotics have their best evidence for diarrhea during antibiotics, not for food sensitivity; see our probiotics page and how to read a probiotic label.
Quick answers
Common questions
4 answersCan an IgG test tell me which foods cause my bloating?
Is IgG the same as a food allergy test?
No. Food allergy involves IgE antibodies, and a person with a true allergy may not have raised IgG to that food2.
Did any study find IgG-based diets helped?
How is lactose intolerance diagnosed?
Usually with a hydrogen breath test after a measured lactose drink, alongside your symptoms and history6.
Keep reading
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References
7 sources. Numbers in the text link here.
Sources cited in this article
7 sources- 1Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force ReportAllergy, 2008 · PMID 18489614
- 2CSACI Position statement on the testing of food-specific IgGAllergy Asthma Clin Immunol, 2012 · PMID 22835332
- 3Unproven Diagnostic Tests for Adverse Reactions to FoodsJ Allergy Clin Immunol Pract, 2018 · PMID 29524991
- 4Food elimination based on IgG antibodies in irritable bowel syndrome: a randomised controlled trialGut, 2004 · PMID 15361495
- 5Diet restriction in migraine, based on IgG against foods: a clinical double-blind, randomised, cross-over trialCephalalgia, 2010 · PMID 20647174
- 6Diagnosis of Lactose IntoleranceNational Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), 2018
- 7Effect of lactase on symptoms and hydrogen breath levels in lactose intolerance: A crossover placebo-controlled studyJGH Open, 2021 · PMID 33490624
Lactase enzyme and other dietary supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA. Talk to your clinician or pharmacist before starting a supplement, especially if you take prescription medicines. This page has no product or affiliate links.