Food Sensitivity Testing: What Works and What's a Waste of Money

The Difference Between Food Allergy and Food Sensitivity

Food allergy (IgE-mediated): Involves the immune system (immunoglobulin E antibodies). Reactions are typically rapid (minutes to 2 hours), potentially severe (anaphylaxis), and reproducible. Diagnosis: allergy clinic, skin prick test, specific IgE blood test. This is mainstream medicine.

Food intolerance/sensitivity: No agreed clinical definition. Reactions are typically delayed (hours to days), dose-dependent, less severe, and inconsistent. No validated biological mechanism or diagnostic test. This is where the alternative testing industry operates.

The IgG Food Testing Problem

The most commonly sold "food sensitivity" test measures IgG antibodies to 100–200 foods. Results typically come back with dozens of "reactive" foods — creating an extensive elimination list.

The problem:

IgG antibodies to food are a normal immune response to eating. Every time you eat a food, your gut-associated immune system produces IgG antibodies to its proteins. People who eat more of a food produce more IgG antibodies to it. This is immune tolerance, not sensitivity.

The British Society for Allergy and Clinical Immunology (BSACI), the European Academy of Allergy and Clinical Immunology (EAACI), and the British Dietetic Association (BDA) all state that IgG food sensitivity tests are not validated, not diagnostic, and should not be used to guide dietary decisions.

A 2018 BDA position statement: "There is no credible evidence that IgG food antibody testing can diagnose food intolerance or sensitivity."

Despite this, these tests are sold by many wellness clinics and practitioners for £200–400.

What Actually Causes Food Sensitivities?

FODMAPs: Fermentable short-chain carbohydrates that cause gas, bloating, and bowel changes. Not an immune reaction. Managed by the low-FODMAP diet (evidence-based, developed at Monash University).

Lactose intolerance: Deficiency of lactase enzyme. Not immune-mediated. Diagnosed by hydrogen breath test or clinical response.

Non-coeliac gluten sensitivity (NCGS): A genuine but poorly understood condition. No specific biomarker. Diagnosed by exclusion of coeliac disease (TTG-IgA blood test + endoscopy) and wheat allergy, followed by double-blind gluten challenge.

Histamine intolerance: Impaired DAO enzyme (histamine-degrading) leading to excess histamine from fermented foods, aged cheese, wine, canned fish. No validated test. Managed by low-histamine diet and DAO enzyme supplementation.

Coeliac disease: Immune-mediated (but not IgG-based — it's IgA-mediated). Properly diagnosed by TTG-IgA blood test and small intestinal biopsy. Do not start gluten-free diet before testing.

Validated Approaches to Food Sensitivity Investigation

Step 1: Exclude medical causes Your GP should rule out: coeliac disease (TTG-IgA blood test), inflammatory bowel disease (faecal calprotectin), lactose intolerance (hydrogen breath test), thyroid disease, and colon cancer (particularly if new symptoms, age > 50, or family history).

Step 2: Symptom diary Two weeks of food and symptom logging. Many people identify their trigger foods this way without expensive testing.

Step 3: Low-FODMAP diet (if IBS is suspected) Done under dietitian guidance. Three phases: strict elimination (6 weeks), structured reintroduction (8 weeks), long-term personalisation. 70–75% of IBS patients see significant improvement.

Step 4: Elimination and rechallenge (if a specific food is suspected) Eliminate the suspected food for 4–6 weeks. Reintroduce and observe. Simple, free, and the gold standard for identifying specific food sensitivities.

Supplements That May Help While Investigating

Peppermint oil (enteric-coated): For general IBS-C/IBS-D symptom management while identifying triggers.

Digestive enzymes: Particularly alpha-galactosidase (Beano) for legume-related gas; lactase supplements for lactose.

Magnesium citrate: For constipation-predominant gut issues.

Probiotics: For restoring microbiome balance post-antibiotic.

Bottom Line

Save your £200–400 on IgG food sensitivity testing. The results are not clinically meaningful and the BDA explicitly cautions against acting on them.

Instead: see your GP, get coeliac ruled out, keep a food diary, and if symptoms persist, get a referral to a registered dietitian for low-FODMAP guidance.

Gut symptoms that are persistent, severe, or accompanied by blood, unexplained weight loss, or nocturnal symptoms should be assessed urgently by a doctor.