IgG Food Sensitivity Tests

Food · §297

For roughly the price of a nice dinner you get a small box, a finger-prick lancet, and two weeks later a colourful report telling you the dairy, wheat, and eggs in your normal diet are "reactive" and should go. The catch is what the test actually measures. The antibodies it counts — IgG, especially the IgG4 subclass — go up in everyone who eats food, and the strongest finding in immunology is that they mark tolerance, not trouble. The American, European, Canadian, and Australasian allergy societies have all said don't order this, in language that's unusually direct for a contested topic.

Avoid · As-needed Evidence Strong Chapter Food

A panel runs $200–500 and the list of "reactive" foods that comes back is mostly what's already in your fridge. The allergy-immunology field is unanimous against the test — American, European, Canadian, and Australasian societies all say skip. The bigger cost is the diet that follows: real nutritional gaps, a slow slide into restrictive eating, and a real chance of missing the treatable diagnosis that was hiding behind your symptoms.

IgG antibodies to food are how a normal immune system remembers what you eat. Every time a small amount of digested protein crosses your gut lining and bumps into a B cell, the body builds antibodies against it — that's the immune system doing its job, not a disease state. The subclass these panels mostly read out, IgG4, is the one immunologists associate most strongly with the body learning to tolerate something. When allergists desensitise a peanut-allergic kid through years of carefully escalated peanut exposure, the marker that goes up alongside their growing tolerance is peanut-specific IgG4 Aalberse et al. 2009. The structural quirk that makes IgG4 a tolerance signal — it can't crosslink the receptors that trigger inflammation, and it can't activate complement — is the same quirk that means it cannot drive the symptoms vendors claim it does Aalberse et al. 2009.

This is why the report comes back looking suspiciously like your shopping list. People who drink milk daily score high on milk. People who eat bread daily score high on wheat. Vegans return reactive-egg-and-dairy panels that read clean; carnivores return reactive-beef-and-chicken panels. The European allergy society's 2008 task force summarised this in one sentence: food-specific IgG4 reflects exposure to food, not an adverse reaction to it Stapel et al. 2008.

What the trials actually show

The cleanest fact is that the position statements line up. The American Academy of Allergy, Asthma & Immunology lists IgG food testing in its Choosing Wisely "don't order this" set AAAAI 2019. The European task force calls the test "irrelevant for the laboratory work-up of food allergy or intolerance" Stapel et al. 2008. The Canadian society "strongly discourages" the practice and names nutritional deficiency as a downstream harm Carr et al. 2012. The Australasian society puts it under "unorthodox testing" not supported by evidence ASCIA 2023. These groups don't agree on much in the weeds of allergy practice; on this they agree.

The proponent literature leans on one trial — a 2004 IBS study where patients on an IgG-guided elimination diet improved more than patients on a sham diet. The effect was small, the result lost statistical significance once dropouts were accounted for properly, the test manufacturer paid for the trial, and the foods most commonly excluded in the "real" arm were wheat and dairy — both of which independently relieve IBS symptoms through carbohydrate and lactose mechanisms that have nothing to do with IgG Atkinson et al. 2004 Hunter 2005.

The basic reliability is also poor. Send two tubes of the same blood to two labs (or the same lab twice) and the lists of "reactive" foods that come back are visibly different Mullin et al. 2010 Hodge et al..

The "delayed allergy" misnomer

The pitch you'll hear most often is that IgG is the "delayed" version of allergy testing — IgE for the bee-sting, throat-closing reactions, IgG for the slow ones that show up the next day as a headache, brain fog, or a bloated belly. The framing is wrong on the biology. There is no recognised "IgG-mediated food allergy" disease. The real non-allergic-but-immune food conditions — coeliac disease, eosinophilic esophagitis, food protein-induced enterocolitis — each have their own validated workup (a biopsy, a scope, a structured challenge), and none of those workups touches a generic 90-food IgG panel Sicherer & Sampson 2018 Kelso 2018.

The second-most-common framing is that "even if it's not allergy, it's intolerance or inflammation." Food intolerances with actual mechanisms — lactose, fructose, histamine, fermentable carbs (FODMAPs), gluten in coeliac — are diagnosed by breath tests, gene tests, biopsy, or a careful eliminate-then-reintroduce protocol Lomer 2015. There is no validated blood marker of "food inflammation," and IgG isn't a stand-in for one.

What goes wrong when people act on the report

The result page usually flags somewhere between 15 and 40 foods. Following the advice means a months-long elimination diet that eats most of the way through normal family cooking. Four downstream harms show up in the specialty literature often enough to be worth knowing about:

Nutritional gaps. Dairy out takes calcium with it; wheat out chips into fibre and B vitamins; eggs out drops protein and choline. In children, paediatric allergists have reported cases of severe malnutrition — including kwashiorkor — after parents followed multi-food IgG eliminations Carr et al. 2012.
Disordered-eating slope. A medical-looking report giving you permission to remove half your fridge is a known entry point into orthorexia and avoidant/restrictive eating, especially in teenagers and patients already inclined to restrict. "The test told me to" is the part that's particularly hard to argue with at the dinner table Hammond & Lieberman 2018 Kelso 2018.
Missed real diagnoses. The symptoms that send people to these tests — chronic stomach pain, fatigue, joint aches — sometimes have a real, treatable cause behind them: coeliac disease, inflammatory bowel disease, true IgE allergy, thyroid trouble. Months on an IgG-guided elimination push that diagnosis back, sometimes by years Stapel et al. 2008 Boyce et al. 2010.
Lost tolerance to a real allergen. Adults with a genuine but mild IgE allergy keep it mild partly through ongoing trace exposure. Strict elimination for months on the back of an IgG report can hand them a more dangerous reaction the day they reintroduce the food Stapel et al. 2008.

What actually finds the food that's hurting you

If a specific food really is causing a reaction, the workup depends on the kind of reaction.

For anything that looks like classic allergy — hives, swelling, breathing trouble within minutes to two hours of eating — that's a job for an allergist with skin-prick testing, specific IgE blood tests, and where needed an oral food challenge under medical supervision. The food challenge is the gold standard the rest of the workup is calibrated against Sicherer & Sampson 2018.

For chronic gut symptoms — bloating, pain, irregular stool, fatigue with meals — the first step is a GP visit and a coeliac blood test (cheap, covered, and a real diagnosis if positive). If coeliac is ruled out and IBS is the working diagnosis, the protocol with actual trial evidence is a structured elimination diet — the low-FODMAP version, supervised by a dietitian: cut out a defined list of fermentable carbs for a few weeks, reintroduce them one at a time, identify the specific triggers Lomer 2015. That protocol has positive trials behind it; the IgG-guided version does not.

For everything in between — fatigue, brain fog, joint aches, mood swings — the honest answer is that "food sensitivity" is rarely the primary culprit in adults eating a reasonable diet, and the workup is sleep, stress, thyroid, anaemia, and the rest of normal medicine before going looking for a hidden food.

What the test costs and how it gets sold

Retail panels run $140 to $500, ordered online, with a finger-prick kit and a mail-in tube. Results land in one to three weeks as a colour-graded list of foods. Insurance does not cover them in the US, Canada, UK, or Australia. The same panel sold through a functional-medicine clinic typically comes bundled with a consult and a supplement protocol, and can run well into four figures by the time the elimination "phase" is over and the retest is ordered six months later. Almost no result page carries a clear "this test does not diagnose allergy or intolerance" notice on the result itself; the disclaimer, when it exists, is several clicks deep in the FAQ.

What happens if the report keeps running the kitchen

The first month feels like control. You have a printed list. You can point at it. Dinner gets simpler — by force.

By month three the list has narrowed twice and you're declining lunch invitations because the work cafeteria has nothing on it. Your partner has started cooking two versions of dinner; your kids notice. The symptoms you ordered the test for haven't really shifted. The natural next move is the retest — and the new report flags a slightly different set of foods, because what you've been eating has changed. The diet narrows again.

By year one a fair number of people in this loop have lost noticeable weight, had their iron or B₁₂ flagged low on routine bloods, and noticed meals out have stopped being relaxing. A subset — the specialty literature flags adolescents and women in their twenties especially — find that the relationship with food has crossed a line it shouldn't have, and walking it back takes longer than the elimination did Hammond & Lieberman 2018. The treatable thing that was actually going on with your gut — coeliac, IBS, IBD, gallbladder, anxiety — is still untreated, because the months and the attention went to chasing the wrong target Carr et al. 2012.

What changes when you stop treating the report as data

Putting the report in a drawer and going back to the foods on it tends to be uneventful. Most of those foods weren't bothering you, which is the whole point of the position statements Stapel et al. 2008. Within a few weeks dinner gets boring again in a good way: you're not auditing it. Within a couple of months iron and B₁₂ on a routine blood draw look normal again; clothes fit. The smaller, harder part is what happens with the symptoms that started the whole thing. If they were a real diagnosis — coeliac, IBS, IBD, something else — they're still there, and a GP visit and a proper workup finds the answer the panel was never going to. If they were stress, sleep, or anxiety, those are also still there, and they get treated through their own channels. The thing the test promised — a clean, quick map from blood draw to the food that's making you sick — was always going to be a fiction; what replaces it is a slower path that ends somewhere real.

Related, if you came in with a real food question

If a food reliably gives you a fast, dramatic reaction, the entry on true food allergy testing (skin-prick, specific IgE, oral challenge) is the next stop. If your symptoms are gut-centred and chronic, look at coeliac screening and the low-FODMAP protocol for IBS. If "food sensitivity" came up because you're already restricting and not feeling great about it, the entries on disordered eating and orthorexia screening are worth a read before the next panel. And the broader entry on direct-to-consumer health tests applies here: most of them sell certainty the underlying assay can't deliver.

Related in the handbook

Alternatives

— Skip the blood panel — a structured elimination-and-reintroduction diet is the real way to find food triggers.
— For gluten specifically, skip the IgG panel: the HLA-DQ2/DQ8 gene test can rule celiac out for life in one draw.

— Real food reactions like histamine intolerance get missed when people chase an IgG report instead.
— People often buy these panels for IBS-type symptoms, but the real, treatable diagnosis hiding behind them is usually something like IBS itself.
— These panels manufacture 'abnormal' results the same way a misread lab range does — a long list of problems you don't actually have.
— These tests are the engine behind a lot of 'leaky gut' diagnoses — same shaky science, same wasted money.
— Like IgG food panels, MTHFR testing is a high-marketing, low-value test the specialty bodies recommend against.
— An IgG panel will often flag wheat — but it can't tell you whether gluten is really your problem.
— Spit-in-a-tube oral microbiome kits are the dental cousin of this test — over-marketed, under-validated, and pointed at products you don't need.

Substance and claimed effects

Direct-to-consumer (DTC) IgG food sensitivity panels measure serum immunoglobulin G (and/or IgG4) antibodies against a panel of 90–250 food antigens, returning a colour-graded list of "reactive" foods the consumer is told to eliminate. Brand names include Everlywell, YorkTest, Cyrex, ALCAT-derivative IgG panels, Pinnertest, ImuPro, FoodMarble-affiliated panels, and dozens of clinic-branded variants. Prices range from roughly $140–500 per test; some functional-medicine clinics bundle panels into multi-hundred-dollar workups. Marketed claims span irritable bowel syndrome, migraine, fatigue, brain fog, eczema, weight gain, autoimmune symptoms, mood disturbances, and "leaky gut." This entry covers the test's clinical validity, the effect of acting on its results on diet, cost, and downstream restriction patterns, and the unified position of major allergy/immunology bodies. It does not cover validated allergy diagnostics (skin-prick, specific IgE, oral food challenge) or genuine non-IgE-mediated food intolerances such as lactase deficiency, FODMAP sensitivity, fructose malabsorption, or celiac disease — those are separate entries.

Evidence by addressing question

Mechanism — what IgG to food actually represents

Science. IgG antibodies to dietary proteins are produced by virtually everyone with a functioning immune system following gut exposure to food antigens that cross the intestinal mucosa Stapel et al. 2008. The strongest mechanistic finding: IgG4 — the subclass most DTC tests measure — is generated as part of immune tolerance, not pathology. In allergen-specific immunotherapy (the gold-standard treatment that desensitises true IgE allergy), rising food- or allergen-specific IgG4 tracks clinical improvement; IgG4 is a "blocking antibody" that competes with IgE for allergen binding and dampens mast-cell degranulation Aalberse et al. 2009. IgG4 lacks the structural features needed to crosslink Fc receptors or fix complement, so it cannot drive the inflammatory cascades the marketing materials invoke Aalberse et al. 2009.

The cleanest demonstration that food-IgG reflects exposure rather than disease: in cohorts of healthy controls without symptoms, food-specific IgG concentrations correlate tightly with reported consumption frequency of the corresponding foods Stapel et al. 2008 Carr et al. 2012. People who drink milk daily have high anti-milk IgG. People who eat wheat have high anti-wheat IgG. The test is, mechanistically, a memory of what the patient eats, not a marker of what is making them sick.

Mechanism gap on the proponent side. Vendor literature variably invokes "Type III hypersensitivity," "delayed hypersensitivity," "immune-complex deposition," or "leaky gut." Type III reactions (immune-complex disease — serum sickness, lupus nephritis) require sustained high-titer antibodies with complement activation, occur at predictable latency, and have characteristic histology; no such picture is reproducible from food-IgG, and IgG4 cannot mediate the mechanism at all Stapel et al. 2008 Kelso 2018 Gocki & Bartuzi 2016. The "leaky gut" framing has no validated assay, no consensus case definition, and no demonstrated causal link to a food-IgG profile.

Evidence — does the test perform as claimed

Science. No diagnostic-validity study (sensitivity, specificity, positive predictive value against any criterion standard) supports food-specific IgG or IgG4 as a marker of food allergy, food intolerance, IBS, migraine, or any other named condition Stapel et al. 2008 Carr et al. 2012 Kelso 2018 Hammond & Lieberman 2018. Reviews from 2008 forward have asked vendors and proponents to produce such validity data; none has been published.

The two trials proponents most often cite:

Atkinson 2004 (Gut). 150 IBS patients randomised to a "true" IgG-guided elimination diet vs. a sham diet; the IgG arm reported a 10% greater reduction in symptom score over 12 weeks, with the difference reaching statistical significance only in completers, not intention-to-treat with imputation Atkinson et al. 2004. The trial's funder, York Nutritional Laboratories, manufactured the test. The accompanying editorial argued the effect plausibly reflects expectation and partial unblinding (subjects had to follow a list of restricted foods specific to their result, making allocation guessable), and noted that wheat and milk dominated both arms' exclusion lists — both foods independently linked to IBS-symptom relief through FODMAP/lactose mechanisms unrelated to IgG Hunter 2005.
Zar 2005 (Scand J Gastroenterol). Open-label exclusion of high-IgG4 foods in 25 IBS patients improved symptom and rectal compliance scores at 6 months Zar et al. 2005. No control arm; the design cannot separate dietary restriction from placebo, regression to mean, or shared exclusion of common FODMAP-rich foods.

Against these, an RCT in migraine using the same IgG-guided design (167 patients, randomised true vs. sham elimination, 12 weeks) found no difference between arms on headache days or migraine days — the test added nothing over sham restriction Mitchell et al. 2011. Across rheumatic disease, atopic dermatitis, autism, and ADHD, no RCT has shown IgG-guided elimination outperforming sham Kelso 2018 Hammond & Lieberman 2018.

Test-retest and inter-laboratory reproducibility are also poor. Independent comparisons of duplicate blood samples sent to the same vendor and to different vendors produce substantially different "reactive food" lists for the same individual — a basic reliability failure on top of the absent validity Hodge et al.Mullin et al. 2010.

Practice / clinical consensus — the position of the field is unified and unusually blunt:

EAACI (European Academy of Allergy and Clinical Immunology), 2008. Task force statement: "Food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints" Stapel et al. 2008.
AAAAI (American Academy of Allergy, Asthma & Immunology). Endorsed the EAACI position Bock 2010 and, via the Choosing Wisely campaign, lists IgG food testing among the top tests not to order: "Don't perform unproven diagnostic tests, such as immunoglobulin G (IgG) testing… in the evaluation of allergy" AAAAI 2019.
CSACI (Canadian Society of Allergy and Clinical Immunology), 2012. "The use of serum-specific IgG testing to diagnose food allergy or intolerance is unproven and may lead to unnecessary changes in diet and possible nutritional deficiencies. The CSACI strongly discourages this practice" Carr et al. 2012.
ASCIA (Australasian Society of Clinical Immunology and Allergy). Lists IgG food panels under "unorthodox testing" not supported by evidence and warns against acting on results ASCIA 2023.
NIAID Expert Panel Guidelines (US), 2010. Recommend against the use of "nonstandardized and unproven tests" including food-specific IgG for diagnosing food allergy Boyce et al. 2010.

The unanimity is unusual. The AAAAI, EAACI, CSACI, and ASCIA disagree on plenty within allergy and immunology; on IgG food panels, every major specialty body has independently arrived at the same position over a fifteen-year span. No allergy/immunology body endorses the test.

Misconceptions — IgG is "the delayed allergy test"

The most common consumer-facing framing positions IgG panels as a complement to IgE allergy testing — "IgE is immediate, IgG is delayed." This is wrong on the immunology. There is no established "delayed IgG-mediated food allergy" disease entity; non-IgE-mediated food allergies (FPIES, allergic proctocolitis, eosinophilic esophagitis, celiac disease) have their own validated diagnostic pathways and none uses generic food-IgG panels Sicherer & Sampson 2018 Kelso 2018. The "delayed allergy" framing also lets the test capture symptom attributions — fatigue, brain fog, joint aches — that have no immunological link to the foods tested.

A second common framing: "even if not allergy, IgG identifies food intolerance / inflammation." Food intolerances with known mechanisms (lactose, fructose, histamine, FODMAPs, gluten in celiac/NCGS, sulfites) are diagnosed with breath tests, gene tests, biopsy, or structured elimination — not antibody panels Lomer 2015. There is no validated "food inflammation" biomarker that food-IgG measures.

Practicalities — cost, access, what the report looks like

Retail DTC panels cost $140–500; finger-prick collection at home, mail-in, results in 1–3 weeks. Reports return a colour-coded list (often red/amber/green) with 20–80 foods flagged as "reactive." Most reports lack any clinical-validity disclaimer; some now carry small-print acknowledgement that the test does not diagnose allergy or intolerance — usually deep in the FAQ rather than on the result page. Insurance does not cover the tests in the US, Canada, UK, or Australia; clinic-administered versions billed as "food sensitivity workups" through functional-medicine practices can run into four figures when combined with consultations and recommended supplement protocols Carr et al. 2012 Mullin et al. 2010.

Contraindications and failure modes — what the test causes when acted on

Acting on an IgG report typically produces a multi-food elimination diet (median ~20 foods, sometimes 40+) sustained for weeks to months. Documented harms:

Nutritional restriction without medical indication. Eliminating common high-IgG foods — dairy, wheat, eggs, soy, common nuts, beef — removes major sources of calcium, B₁₂, iron, iodine, and protein. Pediatric cases of kwashiorkor and severe failure-to-thrive have been reported after parents eliminated multiple foods based on IgG panels Carr et al. 2012 Hammond & Lieberman 2018.
Eating disorder onset and exacerbation. Allergy/immunology and eating-disorder specialists have flagged DTC food panels as an entry pathway into orthorexia and ARFID, particularly in adolescents and patients with existing restrictive tendencies; "the test told me to" provides medicalised cover for restriction Kelso 2018 Hammond & Lieberman 2018.
Missed real diagnoses. Patients pursuing IgG-guided elimination for symptoms caused by IBD, celiac disease, true IgE-mediated allergy, eosinophilic esophagitis, or non-GI causes delay correct workup. The unanimous specialty-society warning specifically calls out delayed diagnosis as a harm Stapel et al. 2008 Carr et al. 2012 Boyce et al. 2010.
Loss of acquired tolerance to true allergens. Patients with prior IgE-mediated allergy who eliminate trace exposures based on an IgG result may lose the tolerance maintained by ongoing low-level exposure — and reintroduce with anaphylaxis risk Stapel et al. 2008.
Reinforcement of false illness model. When elimination "works" (via FODMAP coincidence, placebo, structured eating displacing junk, or attention to food), the IgG model is confirmed in the patient's mind and the next round of testing follows.

Alternatives — what actually diagnoses food problems

For suspected IgE-mediated allergy: skin-prick test, serum-specific IgE, and oral food challenge as the criterion standard, ordered by an allergist Sicherer & Sampson 2018 Boyce et al. 2010. For non-IgE conditions: gastroenterology workup including celiac serology and biopsy, IBD evaluation, hydrogen/methane breath tests for lactose and fructose, and structured low-FODMAP elimination–reintroduction supervised by a dietitian for IBS Lomer 2015. The low-FODMAP protocol — eliminate, reintroduce, identify specific triggers — has positive trial data in IBS that IgG-guided elimination does not.

Stakes — what continues to happen if the test stays in the household

The substance here is the test as a decision input, not the test as a laboratory artifact. The relevant stakes are continued spending on retests, periodic re-elimination cycles, slow narrowing of the family diet, and the opportunity cost of months spent ruling out foods while an underlying condition (celiac, IBD, IgE allergy, anxiety, IBS managed correctly) goes untreated. Scale: the global DTC food-sensitivity-test market was estimated at over $500M USD by independent industry analysts in the early 2020s; on the consumer side this is a high-traffic category despite uniform specialty opposition.

Payoff — what happens when the test stops driving decisions

Stopping IgG-driven elimination and pursuing validated workup tends to either confirm a treatable real diagnosis (celiac, lactose intolerance, FODMAP responder, IgE allergy, IBD) or — more commonly — return the patient to a normal varied diet with symptoms managed through standard channels (stress, sleep, fibre, low-FODMAP trial, treating anxiety). Reintroducing eliminated foods is uneventful for the overwhelming majority because there was no real reaction to begin with Stapel et al. 2008.

The credibility range

Optimist case

The strongest pro-test position runs as follows. (1) Some IgG-guided RCTs in IBS show statistically significant symptom improvement over sham elimination, notably Atkinson 2004 Atkinson et al. 2004 and supportive case-series in IBS and migraine. (2) Food-IgG is correlated with exposure, but high-exposure foods that the patient consumes daily may be the same foods causing low-grade GI inflammation; the test thus provides a starting point for elimination even if the immunological story is wrong. (3) Structured elimination of any kind benefits a fraction of IBS, migraine, and eczema patients; if the IgG panel is what gets a patient to do structured elimination, the consumer benefit is real even if the mechanism on the box is wrong. (4) Patient-reported outcomes from large user populations include genuine relief that should not be dismissed as pure placebo.

Skeptic case

The counter-case is overwhelming. (1) Mechanistically, IgG4 is a tolerance marker; the test measures what the patient eats, not what makes the patient sick Stapel et al. 2008 Aalberse et al. 2009. (2) The cited "positive" trial in IBS lacks intention-to-treat significance, was funded by the test manufacturer, suffered partial unblinding, and is confounded by FODMAP/lactose effects from the foods most commonly eliminated Hunter 2005. (3) The migraine RCT using identical design was null Mitchell et al. 2011. (4) Inter-laboratory reproducibility is poor; same blood, different "reactive foods" Mullin et al. 2010 Hodge et al.. (5) Every major allergy/immunology society — across four continents and a fifteen-year span — independently recommends against the test, with several characterising it as actively harmful Stapel et al. 2008 Carr et al. 2012 AAAAI 2019 ASCIA 2023. (6) Documented harms — pediatric malnutrition, eating disorder onset, missed celiac and IBD, loss of tolerance to true allergens — are real, not hypothetical Carr et al. 2012 Hammond & Lieberman 2018. (7) The "structured elimination helps some patients" defence applies equally to non-IgG-guided elimination (low-FODMAP, simple journaling, eliminate-and-reintroduce) at zero test cost and lower restriction severity.

Author's call

This is one of the clearest "do not buy this product" calls in nutrition. The evidence on test validity is decisively negative, the mechanism the test invokes is wrong (IgG4 marks tolerance, not pathology), specialty consensus across continents is unanimous, and the harms — financial, nutritional, psychological, diagnostic — are well-documented. The optimist case reduces to "structured elimination sometimes helps some symptoms," which is true and irrelevant: structured elimination should be guided by a validated protocol (low-FODMAP, supervised allergen elimination after proper allergy workup, celiac-negative gluten trial) at zero test cost. Meta scores reflect: high evidence (the negative evidence is robust and consistent), low controversy within allergy/immunology (the field is unanimous) but visible controversy in the broader public-facing nutrition space where the tests are sold. Action: avoid the test; if symptoms warrant workup, see a GP or allergist.

Stakeholder and incentive map

Commercial. DTC labs (Everlywell, YorkTest, Cyrex, Pinnertest, ImuPro, and a long tail of clinic-branded resellers). Margins on a $200 ELISA panel are large; repeat-test cycles ("retest after 6 months on elimination") amplify lifetime value. Industry has funded several of the supportive trials Atkinson et al. 2004 and underwrites practitioner-education content. The functional-medicine and integrative-medicine practice channels are major revenue partners.
Practitioner subculture. Functional-medicine MDs, naturopaths, some chiropractors and nutritionists, and a portion of registered dietitians offer IgG panels as a workup tool. The professional incentive is real — the panel justifies a paid consult and an elimination protocol with follow-up visits.
Patient community. Online communities (IBS, migraine, autoimmune, ADHD, autism, "leaky gut") amplify positive personal results and trade test recommendations; selection bias in who posts.
Counter-incentives. Allergy/immunology specialty societies (AAAAI, EAACI, CSACI, ASCIA), gastroenterology and dietetics bodies, and eating-disorder clinicians. Insurers also push back through non-coverage, though the test market sidesteps insurance entirely.
Regulators. The US FDA does not regulate these tests as in vitro diagnostics in most cases — they are laboratory-developed tests sold for "informational" use. Marketing claims have occasionally drawn FTC scrutiny but enforcement is light. In Canada, several provincial colleges of physicians have issued advisories against ordering the test.

Population variability

By baseline diet. The test's results are dominated by what the patient eats; a vegan and an omnivore tested on the same panel will return entirely different "reactive food" lists driven by exposure, not pathology.
By age. Children are at especially high risk of harm from acting on results — multi-food elimination during growth has produced reported cases of kwashiorkor and failure-to-thrive Carr et al. 2012. Adolescents are at heightened eating-disorder risk.
By underlying condition. IBS patients who happen to eliminate FODMAP-rich foods following IgG guidance may benefit incidentally; this is not specific to the test. Celiac patients told to "moderate" wheat based on IgG (rather than eliminate strictly based on a celiac diagnosis) are positively harmed by the misframing. Patients with prior IgE allergy face the loss-of-tolerance risk above.
By psychological profile. Patients with health anxiety, somatic symptom focus, or restrictive-eating tendencies report stronger subjective response to the elimination protocol and are also at higher risk for downstream eating-disorder progression Hammond & Lieberman 2018.

Knowledge gaps

What hasn't been studied — and what wouldn't change the call. There is no realistic study design that would validate IgG panels as a food-sensitivity diagnostic, because the underlying immunology has been characterised: IgG and especially IgG4 mark exposure and tolerance, not adverse reaction Aalberse et al. 2009 Stapel et al. 2008. A well-powered, industry-independent, intention-to-treat RCT of IgG-guided vs. sham-guided elimination in IBS that controlled rigorously for FODMAP overlap could in principle re-examine the Atkinson 2004 finding; nothing comparable has appeared in the twenty years since. Patient-level data on harms (eating-disorder incidence following DTC food testing, pediatric nutritional adverse events) is captured only in case reports — a registry-grade harm-tracking study does not exist. What is known is enough: validity is absent, mechanism is wrong, alternatives exist, harms are documented, specialty consensus is unified. The remaining gaps are around prevalence of harm, not around whether the test should be recommended.

Scope versus brief. The brief named diet decisions, expense, dietary restriction patterns, and the position of major allergy/immunology bodies on clinical validity. The article covers all four end to end. No narrowing.

Action choice. Considered know vs avoid. Settled on avoid: the substance being scored is a test that drives concrete behaviour (order/don't order; act on results/don't), so the reader action is concrete rather than passive awareness. Know would understate the recommendation.

Category choice. Considered screening and medical. Settled on food because the substance's downstream consequence is dietary behaviour and the consumer use case is "what should I eat" — squarely food/eating. The entry could reasonably be cross-listed under screening.

Controversy score. Within allergy/immunology the consensus is unusually unified (argues for 0). The test is widely sold and defended in parallel public-facing markets (argues for higher). Landed at 1: there is no field disagreement, but the commercial and patient-community pushback is what the reader will encounter in the wild, and downplaying that to 0 reads as out-of-touch.

Health and mood scoring for an avoid entry. Scored as the benefit of avoidance — nutritional adequacy preserved, eating-disorder slope avoided. Kept modest (1 and 2): the harm hits a minority hard, not the median user, and the score reflects expected effect across the population the entry is written for.

Optimist case in the body. Atkinson 2004 IBS finding is addressed inside the evidence section with the manufacturer-funding and FODMAP-confound caveats, rather than steel-manned in a separate passage; the fuller credibility-range discussion lives in the research dossier. This avoids strawmanning while keeping the article landed.

Separate-entry candidates surfaced.

Low-FODMAP protocol for IBS (referenced; warrants its own entry).
Coeliac screening as a screening entry.
Direct-to-consumer health tests as a category entry — the recurring "an assay packaged as actionable when the underlying assay isn't" pattern (mineral hair analysis, ALCAT, food-IgG, some bloodwork panels).
Orthorexia / restrictive eating screening — the eating-disorder slope flagged here deserves a deeper home.
Food allergy testing (skin-prick, specific IgE, oral challenge) as a true-positive sibling.

Future link candidates. Once they exist, wire in: food allergy testing, coeliac screening, low-FODMAP for IBS, orthorexia/restrictive eating, direct-to-consumer health tests category.

Excluded sibling tests. Mediator-release tests (MRT/LEAP), ALCAT, electrodermal testing, applied kinesiology, hair-analysis food panels all share the "unproven food-sensitivity workup" critique. Folding them in would dilute the IgG focus and confuse mechanism stories; better as a sibling entry or a category-level entry.

Excluded adjacent conditions. Histamine intolerance and mast cell activation syndrome are frequently confused with the IgG framing in lay discussion but are distinct enough to warrant their own entries.

Contraindications field intentionally empty. The closed vocabulary is designed for "do" entries — listing eating-disorder-history here would risk reading as "the test is fine except for this group" when the entry's stance is "skip across the board, more strongly so for this group." The eating-disorder risk is named in failure-modes and stakes instead.